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This file describes the BASH debugger, the BASH symbolic debugger.
This is the 3.1-0.06 Edition, 18 July 2006, for BASH.
Copyright (C) 2002, 2003, 2004, 2006 Rocky Bernstein.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
| 1. Summary of the BASH Debugger | Overview of Debugger with a sample session | |
| 2. Getting in and out | ||
| 3. Script Setup inside the BASH Debugger | Script setup inside the BASH debugger | |
| 4. BASH Debugger Command Reference | BASH debugger command reference | |
| 5. Using the BASH debugger from a front-end user interface | Using the Debugger from a front-end user interface | |
| 6. Reporting Bugs | Reporting bugs | |
| 7. History and Acknowledgments | ||
Appendices | ||
| A. GNU GENERAL PUBLIC LICENSE | GNU General Public License says how you can copy and share bashdb | |
| B. GNU Free Documentation License | The license for this documentation | |
Indexes (nodes containing large menus) | ||
| Function Index | An item for each function name. | |
| Command Index | An item for each command name. | |
| Variable Index | An item for each documented variable. | |
| General Index | An item for each concept. | |
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The purpose of a debugger such as the BASH debugger going on "inside" a bash script while it executes.
the BASH debugger these) to help you catch bugs in the act:
Although you can use the BASH debugger to debug scripts written in BASH, it can also be used just as a front-end for learning more about programming in BASH. As an additional aid, the debugger can be used within the context of an existing script with its functions and variables that have already been initialized; fragments of the existing can be experimented with by entering them inside the debugger.
| 1.1 A Sample BASH Debugger Session | A Sample BASH Debugger session | |
| 1.2 Interactive Line Tracing Session | ||
| Free software | Freely redistributable software |
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You can use this manual at your leisure to read all about the BASH debugger. However, a handful of commands are enough to get started using the debugger. This chapter illustrates those commands.
Below we will debug a script that contains a function to compute the factorial of a number: fact(0) is 1 and fact(n) is n*fact(n-1).
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The command invocation uses the option "-L ." Here we assume that
the bashdb script and the debugger files are in the same
location. If you are running from the source code, this will be the
case. However if bashdb has been installed this probably won't be true
and here you probably don't need to use "-L ." Instead you would
type simply bashdb /tmp/fact.sh.
Position information consists of a filename and line number,
e.g. (/tmp/fact.sh:9) and is given parenthesis. This position
format is similar to that used by the Perl debugger and is also in the
same format used by my GNU make debugger (
http://bashdb.sourceforge.net/remake. and Extended python
debugger http://remake.sourceforge.net/remake. GNU Emacs and DDD
can parse this and in fact the same regular expression is used on the
3 debuggers.
The first debugger command we gave -, we listed a window of lines before where we were executing. Because the window, 10 lines, is larger than the number of lines to the top of the file we printed only 9 lines here. The next command list starting from the current line and again wants to print 10 lines but because there are only one remaining line, that is what is printed.
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Ooops... The variable n isn't initialized.
The first step command steps the script one instruction. It may seem odd that the line printed is exactly the same one as before. What has happened though is that we've "stepped" into the subshell needed to run `fact 0`; we haven't however started running anything inside that subshell yet though.
To indicate that which piece of the multi-part line echo fact 0
is: `fact 0` we show that part all by itself fact 0. If nothing
is shown then it means we are running the beginning statement or in
this case the outermost statement.
To indicate that we are now nested in a subshell, notice that the command number, starting with 3, or the third command entered, now appears in parenthesis. Each subshell nesting adds a set of parenthesis.
The first step command steps the script one instruction; it
didn't advance the line number, 9, at all. That is because we were
stopping before the command substitution or backtick is to take
place. The second command we entered was just hitting the return key;
bashdb remembers that you entered step previously, so it runs
the step rather than next, the other alternative when you hit
RET. Step one more instruction and we are just before running
the first statement of the function.
Next, we print the value of the variable n. Notice we need to add a preceding dollar simple to get the substitution or value of n. As we will see later, if the pe command were used this would not be necessary.
We now modify the file to add an assignment to local variable n and restart.
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This time we use the list debugger command to list the lines in
the file. From before we know it takes three steps commands
before we get into the fact() function, so we add a count onto the
step command. Notice we abbreviate step with s;
we could have done likewise and abbreviated list with l.
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Again we just use RET to repeat the last step
commands. And again the fact that we are staying on the same line 4
means that the next condition in the line is about to be
executed. Notice that we see the command (echo 1 or
return) listed when we stay on the same line which has multiple
stopping points in it. Given the information above, we know that the
value echo'ed on return will be 1.
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We saw that we could step with a count into the function
fact(). However above took another approach: we set a stopping point or
"breakpoint" at line 5 to get us a little ways into the fact()
subroutine. Just before line 5 is to executed, we will get back into
the debugger. The continue command just resumes execution until
the next stopping point which has been set up in some way.
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In addition to listing by line numbers, we can also list giving a function name. Below, instead of setting a breakpoint at line 5 and running "continue" as we did above, we try something slightly shorter and slightly different. We give the line number on the "continue" statement. This is a little different in that a one-time break is made on line 5. Once that statement is reached the breakpoint is removed.
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When we stop at line 5 above, we have already run fact(0) and output
the correct results. The output from the program "fact 0 is: 1" is
intermixed with the debugger output. The T command above
requests call stack output and this confirms that we are not in the
fact(0) call but in the fact(3) call. There are 4 lines listed in the
stack trace even though there is just one call from the main
program. The top line of the trace doesn't really represent a call,
it's just where we currently are in the program. That last line is an
artifact of invoking bash from the bashdb script rather than running
bash --debugger.
The last message in the output above `Debugged program exited
normally.' is from the BASH debugger; it indicates script has finished
executing. We can end our bashdb session with the bashdb
quit command.
Above we did our debugging session on the command line. If you are a GNU Emacs user, you can do your debugging inside that. Also there is a(nother) GUI interface called DDD that supports the BASH debugger.
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One of the things I've always found annoying about set -x
tracing is that there is no position information given in the trace
output, in particular the line number and the file name. Although
function nesting information is shown, other important Information
such as BASH shell and subshell nesting count is not.
From a programming standpoint, these are just as important because
they affect the namespace, or the scope over which variables are seen.
Although I this is best fixed inside BASH, the debugger provides a means for showing position information when tracing a script. Here's a simple session.
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An explanation of the output. The level is how many invocations
of BASH are in effect before the statement shown is
executed. The subshell is how many subshells you are nested
in. Subshells are used by command substitution--`..' and
$(...)--as well as arithmetic expressions ((...)). The
depth is the function depth or how many calls you are nested
in. A "source" command also increases this depth.
Notice also that in contrast to set -x tracing, the line shown
is exactly as you entered it in the source. So if you indented
statements in a meaningful way, it will help you understand the
statement nesting level. But as before, if a line contains multiple
statements, you are not executing the first statement in the
line and set showcommand is not turned off (by default it is
on), that statement is shown in addition below the multi-statement
line. Such an example can be seen right at the beginning where
fact 0 is shown.
If what you want to do is trace the entire script as was done
above (and not stop in the debugger when the script is over), you can
get the same effect by using the -X or --trace option on
the bashdb command:
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the BASH debugger General Public License (GPL). The GPL gives you the freedom to copy or adapt a licensed program--but every person getting a copy also gets with it the freedom to modify that copy (which means that they must get access to the source code), and the freedom to distribute further copies. Typical software companies use copyrights to limit your freedoms; the Free Software Foundation uses the GPL to preserve these freedoms.
Fundamentally, the General Public License is a license which says that you have these freedoms and that you cannot take these freedoms away from anyone else.
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The biggest deficiency in the free software community today is not in the software--it is the lack of good free documentation that we can include with the free software. Many of our most important programs do not come with free reference manuals and free introductory texts. Documentation is an essential part of any software package; when an important free software package does not come with a free manual and a free tutorial, that is a major gap. We have many such gaps today.
Consider Perl, for instance. The tutorial manuals that people normally use are non-free. How did this come about? Because the authors of those manuals published them with restrictive terms--no copying, no modification, source files not available--which exclude them from the free software world.
That wasn't the first time this sort of thing happened, and it was far from the last. Many times we have heard a GNU user eagerly describe a manual that he is writing, his intended contribution to the community, only to learn that he had ruined everything by signing a publication contract to make it non-free.
Free documentation, like free software, is a matter of freedom, not price. The problem with the non-free manual is not that publishers charge a price for printed copies--that in itself is fine. (The Free Software Foundation sells printed copies of manuals, too.) The problem is the restrictions on the use of the manual. Free manuals are available in source code form, and give you permission to copy and modify. Non-free manuals do not allow this.
The criteria of freedom for a free manual are roughly the same as for free software. Redistribution (including the normal kinds of commercial redistribution) must be permitted, so that the manual can accompany every copy of the program, both on-line and on paper.
Permission for modification of the technical content is crucial too. When people modify the software, adding or changing features, if they are conscientious they will change the manual too--so they can provide accurate and clear documentation for the modified program. A manual that leaves you no choice but to write a new manual to document a changed version of the program is not really available to our community.
Some kinds of limits on the way modification is handled are acceptable. For example, requirements to preserve the original author's copyright notice, the distribution terms, or the list of authors, are ok. It is also no problem to require modified versions to include notice that they were modified. Even entire sections that may not be deleted or changed are acceptable, as long as they deal with nontechnical topics (like this one). These kinds of restrictions are acceptable because they don't obstruct the community's normal use of the manual.
However, it must be possible to modify all the technical content of the manual, and then distribute the result in all the usual media, through all the usual channels. Otherwise, the restrictions obstruct the use of the manual, it is not free, and we need another manual to replace it.
Please spread the word about this issue. Our community continues to lose manuals to proprietary publishing. If we spread the word that free software needs free reference manuals and free tutorials, perhaps the next person who wants to contribute by writing documentation will realize, before it is too late, that only free manuals contribute to the free software community.
If you are writing documentation, please insist on publishing it under the GNU Free Documentation License or another free documentation license. Remember that this decision requires your approval--you don't have to let the publisher decide. Some commercial publishers will use a free license if you insist, but they will not propose the option; it is up to you to raise the issue and say firmly that this is what you want. If the publisher you are dealing with refuses, please try other publishers. If you're not sure whether a proposed license is free, write to licensing@gnu.org.
You can encourage commercial publishers to sell more free, copylefted manuals and tutorials by buying them, and particularly by buying copies from the publishers that paid for their writing or for major improvements. Meanwhile, try to avoid buying non-free documentation at all. Check the distribution terms of a manual before you buy it, and insist that whoever seeks your business must respect your freedom. Check the history of the book, and try to reward the publishers that have paid or pay the authors to work on it.
The Free Software Foundation maintains a list of free documentation published by other publishers, at http://www.fsf.org/doc/other-free-books.html.
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This chapter discusses how to start the BASH debugger, and how to get out of it. The essentials are:
source ../bashdb-trace and _Dbg_set_trace.
There are also two front-ends available as well. One can also
enter the debugger inside emacs via the command M-x bashdb
after loading Emacs' Grand Unified Debugger, gud. See
Using the BASH debugger from GNU Emacs. And there is
support in a DDD for bash.
| 2.1 Starting the BASH debugger | How to enter the BASH debugger | |
| 2.2 Quitting the BASH debugger | How to leave the BASH debugger | |
| 2.3 Calling the BASH debugger from inside your program | Calling the debugger from inside your program |
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Note: it is important to use a debugger-enabled bash. You will get an error message if the debugger is run under a version of BASH that does not have debugging support.
As mentioned above, one can enter the BASH debugger DDD. However you don't have to use either of these. And these still need a way on their own to get things started.
There are in fact two other ways to start the BASH debugger. The
first way is to pass the `--debugger' option to bash with the
name of your script the scripts arguments following that, or with a
command string (-c).
bash --debugger script script-arguments... bash --debugger -c command-string... |
This calls a debugger initialization script. It works much like a BASH login profile which may set variables and define functions. But this shell profile is customized for debugging and as such arranges for itself to get called before each statement is executed. Although there are some problems at present in I/O redirection that the method described next doesn't have, it is expected that over time more features will be enabled in bash when the `--debugger' option is in effect. By default, both debugging in Emacs via GUD (Using the BASH debugger under Emacs) and debugging via DDD work via this method.
The form `bash --debugger -c ...' can be used to get into the
debugger without having to give a script name to debug. Sometimes you
may want to do this just to see how the debugger works: try some
debugger commands or maybe get online help. If you run ddd
--bash without giving a script name, it in fact uses this form.
In order for the `--debugger' option to work however, you must
have the debugger scripts installed in a place where the BASH debugger
find them. For this reason, in developing the BASH debugger, I use a second
method more often; it doesn't require the bash debugger to be
installed. This method uses another script called bashdb which
after taking its own options takes the name of the script to debugged
and the arguments to pass to that script. Using this method, one
would start the debugger like this:
bash path-to-bashdb/bashdb bashdb-options script script-arguments... |
As with the first method, bash should be a debugger-enabled
bash. If bashdb has the path to bash in it at the top (e.g. via
#!), and bashdb can be found in your program-search
path, then this might be equivalent to the above:
bashdb bashdb-options script script-arguments... |
There are two or three disadvantages however of running a debugger
this way. First $0 will have the value bashdb rather
than the script you are trying to run. For some scripts this may
change the behavior of the debugged script. Second a traceback will
contain additional lines showing the "source"-ing of the debugged
script from bashdb. And third, although this way works better
than the first method, over time this way may come into disuse.
An option that you'll probably need to use if bashdb isn't installed but run out of the source code directory is `-L' which specifies the directory that contains the debugger script files.
You can further control how bashdb starts up by using command-line options. bashdb itself can remind you of the options available.
Type
bashdb -h |
to display all available options and briefly describe their use.
When the bash debugger is invoked either by the bashdb
front-end script or bash --debugging, the first argument that
does not have an associated option flag for bashdb or
bash (as the case may be) is used as the name a the script file
to be debugged, and any following options get passed the debugged
script.
Options for the bashdb front-end are shown in the
following list.
2.1.1 Command-line options for bashdb script | Options you can pass in starting bashdb |
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bashdb script You can run the BASH debugger
mode or quiet mode. If getopts support is available the script
also allows long-form command options.
-h | --helpThis option causes the BASH debugger to print some basic help and exit.
-VThis option causes the BASH debugger no-warranty blurb, and exit.
-c | --command cmdRun the string instead of running a script
-B | --basenameThis option causes the BASH debugger no-warranty blurb, and exit.
-n | --nx | --no-initDo not execute commands found in any initialization files. Normally, BASH executes the commands in these files after all the command options and arguments have been processed. See section Command files.
-q | --quiet"Quiet". Do not print the introductory and copyright messages. These messages are also suppressed in batch mode.
-t | --terminal | --tty tty"Terminal output". Set the file or terminal that you want debugger command output to go to. Note that the debugger output is independent of the debugged script output.
-L | --library directorySet directory where debugger files reside to directory. The
default location is ../lib/bashdb relative to the place that
the bashdb script is located. For example if bashdb is located in
/usr/bin/bashdb, the default library location will be
/usr/lib/bashdb which may or may not exist. If it doesn't
you'll get an error when you run bashdb. Only if the default location
is incorrect, should you need to use the -L option.
-T | --tempdir directorySet directory to use for writing temporary files.
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An interrupt (often C-c) does not exit from the BASH debugger, but
rather terminates the action of any the BASH debugger
progress and returns to the BASH debugger command level. Inside a debugger
command interpreter, use quit command (see section Quitting the BASH debugger).
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Running a program from the debugger adds a bit of overhad and slows down your program quite a bit, and addressing this properly would mean some serious changes to BASH internals.
If you have a configure script generated by autoconf, and you
want to stop in the middle of the script, it can take quite a while.
Another way to get into the debugger is to change the script and make
an explicit call to the debugger. Because the debugger isn't involved
before the first call, there is no overhead and the script will run at
the same speed as if there were no debugger.
There are two parts to calling the debugger from inside the script,
"sourcing" in the debugger code and then making the call calling the
debugger to issue a "step" command. The name of file in
source command is bashdb-trace and it is located in the
directory where the other bash debugger files live. For example on
GNU/Linux if it is in directory /usr/local/share/bashdb, you
would first add to BASH ascript the line:
source /usr/local/share/bashdb/bashdb-trace |
Although I said that running under the debugger adds overhead which
slows down you program, the above command in of it self will
not cause any slowdown. If possible, it's best to put this
somewhere in the main-line code rather than in a function or in a
subshell. If it is put in one of the latter and you step outside of
the subshell or function, some of the global variables set up in
bashdb-trace may be lost. One the other hand if you know your
debugging will be confined to just the scope of the source
command there is no problem.
The second thing that needs to be done is put add statments to start stepping code, and this line looks like this:
_Dbg_set_trace ; : |
(For reasons that are a mystery to me, the stepping seems to kick in only two statments after the call.)
Putting these two components together, here's an example:
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You will be stopped before y=3 in the debugger.
You can also supply options to _Dbg_bash_trace just as you would to
the debugger itself. All of the options listed in Command-line options for bashdb script can be used with the exception of -c (run a
command) and of course you don't supply the name of a BASH script.
For example to suppress the banner you could use _Dbg_bash_trace
-q in the above example.
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| 3.1 Starting your script | ||
| 3.2 Command files | ||
| 3.3 Your script's arguments | ||
| 3.4 Your script's input and output | ||
| 3.5 Script/Debugger Interaction | Keeping out of each other's harm |
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restart [options to debugged script]runRUse the restart command to restart your script under
the BASH debugger. Without any arguments, the script name and parameters
from the last invocation are used. The BASH debugger tries to maintain the
settings, watchpoints, breakpoints, actions and so on. Internally it
uses line numbers and filenames to record he position of interesting
places in your porgram; so if your program changes some or all of
these numbers may be off. Environment variable
BASHDB_RESTART_FILE is and a temporary file are used to signal
a restart, so you shouldn't uset BASHDB_RESTART_FILE (or any
environment variable starting with BASHDB_.
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A command file for the BASH debugger commands. Comments (lines starting with #) may also be included. An empty line in a command file does nothing; it does not mean to repeat the last command, as it would from the terminal.
When you start the BASH debugger, it automatically executes commands from its init files, normally called `.bashdbinit'(1). During startup, the BASH debugger
The init file in your home directory can set options (such as `set complaints') that affect subsequent processing of command line options and operands. Init files are not executed if you use the `-x' option (see section bashdb script options).
On some configurations of the BASH debugger, the init file is known by a different name (these are typically environments where a specialized form of the BASH debugger different name for the specialized version's init file). These are the environments with special init file names:
You can also request the execution of a command file with the
source command:
source filenameExecute the command file filename.
The lines in a command file are executed sequentially. They are not printed as they are executed. If there is an error, execution proceeds to the next command in the file.
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The arguments to your script can be specified by the arguments of the
restart command.
They are passed to a shell, which expands wildcard characters and
performs redirection of I/O, and thence to your script.
restart with no arguments uses the same arguments used by the previous
restart, or those set by the set args command..
set argsSpecify the arguments to be used the next time your program is run. If
set args has no arguments, restart executes your program
with no arguments. Once you have run your program with arguments,
using set args before the next restart is the only way to run
it again without arguments.
show argsShow the arguments to give your program when it is started.
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By default, the script you run under the BASH debugger does input and output to the same terminal that BASH uses. Before running the script to be debugged, the debugger records the tty that was in effect. All of its output is then written to that. However you can change this when using the `bashdb' script using the `-t' option.
info terminalDisplays information recorded by the BASH debugger program is using.
Another way to specify where your script should do input and output is
with the tty command. This command accepts a file name as
argument, and causes this file to be the default for future restart
commands. It also resets the controlling terminal for the child
process, for future restart commands. For example,
tty /dev/ttyb |
directs that processes started with subsequent restart commands
default to do input and output on the terminal `/dev/ttyb' and have
that as their controlling terminal.
An explicit redirection in restart overrides the tty command's
effect on the input/output device, but not its effect on the controlling
terminal.
When you use the tty command or redirect input in the restart
command, only the input for your script is affected. The input
for the BASH debugger
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The BASH debugger and your program live in the same variable space so to speak. BASH does not have a notion of module scoping or lexical hiding (yet) and this then imposes some additional care and awareness.
Most of the variables and functions used inside the BASH debugger
_Dbg_, so please don't use variables or functions with these
names in your program.
Note: there are some other variables that begin with just an
underscore (_); over time these will be phased out. But until
then, avoid those or consult what is used by the debugger. Run
`bashdb --debugger -c 'declare -p'' to list all the variables in
use including those used by the debugger.
A number of the BASH debugger
use; these start with BASHDB_. For example:
BASHDB_INPUT, BASHDB_LEVEL and,
BASHDB_QUIT_ON_QUIT (see section Debug),
BASHDB_RESTART_FILE (see section Starting), to name a
few. Finally, there are some BASH environment dynamic
variables and these start with BASH_. For example
BASH_SUBSHELL (see section Debug), BASH_COMMAND
(see section Command Display), BASH_LINENO, and
BASH_SOURCE to name a few.
In order to do its work The BASH debugger sets up a DEBUG
trap. Consequently a script shouldn't reset this or the debugger will
lose control. The BASH debugger also sets up an EXIT handler so that
it can gain control after the script finishes. Another signal
intercepted is the an interrupt or INT signal. For more
information about signal handling, see section Signals
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You can abbreviate the long name of the BASH debugger
few letters of the command name, if that abbreviation is unambiguous;
and you can repeat the next o rstep commands by typing
just RET. Some commands which require a parameter, such as
print remember the argument that was given to them.
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A BASH debugger command is a single line of input. There is
no limit on how long it can be. It starts with a command name, which
is followed by arguments whose meaning depends on the command name.
For example, the command step accepts an argument which is the
number of times to step, as in `step 5'. You can also use the
step command with no arguments. Some commands do not allow any
arguments.
A blank line as input to the BASH debugger repeat the previous next or step command.
Any text from a # to the end of the line is a comment; it does nothing. This is useful mainly in command files (see section Command files).
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Once inside the BASH debugger, you can always ask it for
information on its commands, using the command help.
helphYou can use help (abbreviated h) with no arguments to
display a short list of named classes of commands:
bashdb<0> help
bashdb commands:
List/search source lines: Control script execution:
------------------------- -------------------------
l [start|.] [cnt] List cnt lines T [n] Stack trace
from line start s [n] Single step [n times]
l sub List source code fn n [n] Next, steps over subs
- or . List previous/current line <CR>/<Enter> Repeat last n or s
w [line] List around line c [linespec] Continue [to linespec]
f filename View source in file L List all breakpoints
/pat/ Search forward for pat b linespec Set breakpoint
?pat? Search backward for pat del [n].. or D Delete a/all breaks
by entry number
Debugger controls: skip skip execution of cmd
------------------------- cl linespec Delete breakpoints by
H [num] Show last num commands line spec
q [exp] or ^D Quit returning exp R [args] Attempt a restart
info [cmd] Get info on cmd. u [n] Go up stack by n or 1.
!n or hi n Run debugger history n do [n] Go down stack by n or 1.
h or ? [cmd] Get help on command W [var] Add watchpoint. If no
info [cmd] Get info on cmd no expr, delete all
show [cmd] Show settings We [expr] Add Watchpoint arith
expr
so file read in dbg commands t Toggle trace
en/di n enable/disable brkpt,
set x y set a debugger variable watchpoint, or display
e bash-cmd evaluate a bash command tb linespec Add one-time break
disp expr add a display expr a linespec cmd eval "cmd" at linespec
M Show module versions A delete all actions
x expr evaluate expression ret jump out of fn or source
(via declare, let, eval) finish execute until return
deb debug into another cond n exp set breakpoint condition
shell script
!! cmd [args] execute shell command "cmd" with "args"
file filename Set script filename to read for current source.
Data Examination: also see e, t, x
-------------------------
p variable Print variable
V [[!]pat] List variable(s) matching or not (!) matching pattern pat
S [[!]pat] List subroutine names [not] matching pattern pat
Readline command line editing (emacs/vi mode) is available.
For more help, type h <cmd> or consult online-documentation.
|
help commandWith a command name as help argument, the BASH
debugger displays short information on how to use that command.
bashdb<0> help list
l linespec List window lines starting at linespec.
l min incr List incr lines starting at 'min' linespec.
l List next window of lines.
l . Same as above.
Long command name: list.
|
In addition to help, you can use the debugger command
info to inquire about the state of your script, or the state of
the BASH debugger
point to all the sub-commands. See section Command Index.
infoThis command (abbreviated i) is for describing the state of
your program. For example, you can list the arguments given to your
script with info args, or list the breakpoints you have set
with info breakpoints. You can get a complete list of the
info sub-commands with help info.
bashdb<0> help info List of info subcommands: info args -- Argument variables (e.g. $1, $2, ...) of the current stack frame. info breakpoints -- Status of user-settable breakpoints info display -- Show all display expressions info files -- Source files in the program info functions -- All function names info line -- list current line number and and file name info program -- Execution status of the program. info signals -- What debugger does when program gets various signals info source -- Information about the current source file info stack -- Backtrace of the stack info terminal -- Print terminal device info variables -- All global and static variable names info warranty -- Various kinds of warranty you do not have bashdb<1> info source Current script file is parm.sh Contains 34 lines. |
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quit [expression]quit [expression [subshell-levels]]qTo exit the BASH debugger, use the quit command (abbreviated
q), or type an end-of-file character (usually C-d). If
you do not supply expression, the BASH debugger
normally or with exit code 0. Otherwise it will terminate using the
result of expression as the exit code.
A simple quit tries to terminate all nested subshells that may
be in effect. If you are nested a subshell, this is normally
indicated in a debugger prompt by the number of parentheses that the
history number is inside -- no parenthesis means there is no subshell
in effect. The dynamic variable BASH_SUBSHELL also contains the
number of subshells in effect.
If you want only to terminate some number of subshells but not all of
them, you can give a count of the number of subshells to leave after
the return-code expression. To leave just one level of subshell
return does almost the same thing. (See see section Returning) There is a subtle difference between the two though:
return will leave you at the beginning of the next statement
while quit may leave you at the place the subshell was invoked
which may be in the middle of another command such as an assingment
statement or condition test.
If the environment variable BASHDB_QUIT_ON_QUIT is set, when the
program terminates, the debugger will also terminate too. This may be
useful if you are debugging a script which calls another script and
you want this inner script just to return to the outer script.
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One important use of a debugger is to stop your program before it terminates so that, if your script might run into trouble, you can investigate and find out why. However should your script accidently continue to termination, the BASH debugger debugger without your explicit instruction. That way, you can restart the program using the same command arguments.
Inside the BASH debugger, your script may stop for any of several reasons,
such as a signal, a breakpoint, or reaching a new line after a
debugger command such as step. You may then examine and
change variables, set new breakpoints or remove old ones, and then
continue execution.
| 4.4.1 Breakpoints, watchpoints (`break', `tbreak', `watch', `watche'...) | Breakpoints, watchpoints (break, tbreak, watch, watche, clear) | |
| 4.4.2 Resuming Execution (`step', `next', `finish', `skip', `continue', `debug', `return') | Resuming execution (continue, step, next, skip, debug) | |
| 4.4.3 Signals |
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A breakpoint makes your script stop whenever a certain point in the program is reached. For each breakpoint, you can add conditions to control in finer detail whether your script stops.
You can set breakpoints with the break command and its variants
(see section Setting breakpoints), to specify the place where
your script should stop by line number. or function name in the
debugged script.
A watchpoint is a special breakpoint that stops your script when the value of an expression changes. There is a different command to set watchpoints (see section Setting watchpoints).
But aside from that, you can manage a watchpoint like any other breakpoint: you delete enable, and disable both breakpoints and watchpoints using the same commands.
You can arrange to have values from your program displayed automatically whenever BASH stops at a breakpoint. See section Automatic display.
The BASH debugger assigns a number to each breakpoint and watchpoint when you create it; these numbers are successive integers starting with one. In many of the commands for controlling various features of breakpoints you use the breakpoint number to say which breakpoint you want to change. Each breakpoint may be enabled or disabled; if disabled, it has no effect on your script until you enable it again.
Watchpoint numbers however are distinguished from breakpoint numbers by virtue of their being suffixed with the either an upper- or lower-case `W'. For example, to enable breakpoint entry 0 along with watchpoint entry 1 you would write `enable 1 2w', the "2w" refers to the watchpoint; "2W" would work just as well.
| 4.4.1.1 Setting breakpoints (`break' `tbreak') | Setting breakpoints (break, tbreak) | |
| 4.4.1.2 Setting watchpoints (`watch', `watche') | Setting watchpoints (watch, watche) | |
| 4.4.1.3 Breakpoint command lists (`commands') | Breakpoint command lists (command) | |
| 4.4.1.4 Deleting breakpoints (`clear', `delete') | Deleting breakpoints (delete, clear) | |
| 4.4.1.5 Disabling breakpoints (`disable', `enable') | Disabling breakpoints (disable, enable) | |
| 4.4.1.6 Break conditions (`condition') | Break conditions (condition) |
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Breakpoints are set with the break command (abbreviated
b).
break functionSet a breakpoint at entry to function function.
break linenumSet a breakpoint at line linenum in the current source file. The current source file is the last file whose source text was printed. The breakpoint will stop your script just before it executes any of the code on that line.
break filename:linenumSet a breakpoint at line linenum in source file filename; filename has to be one of the files previously read in and has to be specified exactly as the name used when read in. For a list of read-in files, use the `info files' command.
break … if condSet a breakpoint with condition cond; evaluate the expression
cond each time the breakpoint is reached, and stop only if the
value is nonzero--that is, if cond evaluates as true. The
expression is evaluated via the let builtin funtion.
`…' stands for one of the possible arguments described
above (or no argument) specifying where to break. The word "if" is
often optional and is necessary only `…' is
omitted. See section Break conditions, for more information on
breakpoint conditions.
Examples:
bashdb<0> break fn1 Breakpoint 1 set in file parm.sh, line 3. bashdb<1> break 28 Breakpoint 2 set in file parm.sh, line 28. bashdb<2> break parm.sh:29 Breakpoint 3 set in file parm.sh, line 29. bashdb<3> break 28 if x==5 Breakpoint 4 set in file parm.sh, line 28. |
tbreak argsSet a breakpoint enabled only for one stop. args are the
same as for the break command, and the breakpoint is set in the same
way, but the breakpoint is automatically deleted after the first time your
program stops there. See section Disabling breakpoints.
info breakpoints [n]info break [n]info watchpoints [n]Print a table of all breakpoints, watchpoints set and not deleted, with the following columns for each breakpoint:
Enabled breakpoints are marked with `1'. `0' marks breakpoints that are disabled (not enabled).
The number of times that breakpoint or watchpoint has been hit.
The arithmetic expression
The filename and line number inside that file where of breakpoint in the script. The file and line are separated with a colon.
If a breakpoint is conditional, info break shows the condition on
the line following the affected breakpoint; breakpoint commands, if any,
are listed after that.
info break displays a count of the number of times the breakpoint
has been hit.
info break with a breakpoint number n as argument lists
only that breakpoint.
Examples:
bashdb<4> info break Breakpoints at following places: Num Type Disp Enb What 1 breakpoint keep y parm.sh:3 2 breakpoint keep y parm.sh:28 3 breakpoint keep y parm.sh:29 4 breakpoint keep y parm.sh:28 No watch expressions have been set. bashdb<5> info break 4 Num Type Disp Enb What 4 breakpoint keep y parm.sh:28 No watch expressions have been set. |
the BASH debugger your script. There is nothing silly or meaningless about this. When the breakpoints are conditional, this is even useful (see section Break conditions).
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You can use a watchpoint to stop execution whenever the value of an
expression changes, without having to predict a particular place where
this may happen. As with the print (see section Examining Data), the idiosyncracies of a BASH or any POSIX shell
derivative suggest using two commands. The watch command is
just for a single variables; the watche command uses the
builtin "let" command to evaluate an expression. If the variable you
are tracking can take a string value, issuing something like
`watch foo' will not have the desired effect--any string
assignment to foo will have a value 0 when it is assigned via
"let."
watch varSet a watchpoint for a variable. the BASH debugger value of var changes. In this command do not add a leading dollar symbol to var.
watche exprSet a watchpoint for an expression via the builtin "let" command.
the BASH debugger
and its value changes. Not that this may not work for tracking
arbitrary string value changes. For that use watch described
earlier.
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commands [bnum]… command-list …endSpecify a list of commands for breakpoint number bnum. The commands
themselves appear on the following lines. Type a line containing just
end to terminate the commands.
To remove all commands from a breakpoint, type commands and
follow it immediately with end; that is, give no commands.
With no bnum argument, commands refers to the last
breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
recently encountered).
Pressing RET as a means of repeating the last debugger command is disabled within a command-list.
You can use breakpoint commands to start your program up again. Simply
use the continue command, or step, or any other command
that resumes execution.
Any other commands in the command list, after a command that resumes
execution, are ignored. This is because any time you resume execution
(even with a simple next or step), you may encounter
another breakpoint--which could have its own command list, leading to
ambiguities about which list to execute.
If the first command you specify in a command list is silent, the
usual message about stopping at a breakpoint is not printed. This may
be desirable for breakpoints that are to print a specific message and
then continue. If none of the remaining commands print anything, you
see no sign that the breakpoint was reached. silent is
meaningful only at the beginning of a breakpoint command list.
The commands echo, output, and printf allow you to
print precisely controlled output, and are often useful in silent
breakpoints.
For example, here is how you could use breakpoint commands to print the
value of x at entry to foo whenever x is positive.
break foo if x>0 commands silent printf "x is %d\n",x cont end |
One application for breakpoint commands is to compensate for one bug so
you can test for another. Put a breakpoint just after the erroneous line
of code, give it a condition to detect the case in which something
erroneous has been done, and give it commands to assign correct values
to any variables that need them. End with the continue command
so that your program does not stop, and start with the silent
command so that no output is produced. Here is an example:
break 403 commands silent set x = y + 4 cont end |
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It may desirable to eliminate a breakpoint or watchpoint once it has done its job and you no longer want your script to stop there. This is called deleting the breakpoint. A breakpoint that has been deleted no longer exists; it is forgotten.
With the clear command you can delete breakpoints according to
where they are in your script. With the delete command you can
delete individual breakpoints, or watchpoints by specifying their
breakpoint numbers. Note: as described below under the "clear"
command, "d" is an alias for "clear", not "delete".
It is not necessary to delete a breakpoint to proceed past it. the BASH debugger automatically ignores breakpoints on the first instruction to be executed when you continue execution.
clearDelete any breakpoints at the next instruction to be executed in the selected stack frame (see section Selecting a frame). When the innermost frame is selected, this is a good way to delete a breakpoint where your script just stopped.
It may seem odd that we have an alias "d" for "clear." It so happens that Perl's debugger use "d" for its delete command and the delete concept in Perl's debugger corresponds to "clear" in GDB. (Perl doesn't have a notion of breakpoint entry numbers). So in order to be compatible with both debugger interfaces, "d" is used as an alias for "clear." Clear?
clear functionclear filename:functionDelete any breakpoints set at entry to the function function.
clear linenumd linenumDelete any breakpoints set at or within the code of the specified line.
delete [breakpoints]Delete the breakpoints, watchpoints specified as arguments.
If no argument is specified, delete all breakpoints (the BASH debugger
confirmation, unless you have set confirm off). You can
abbreviate this command as de.
Note that for compatibility with Perl's debugger, d means
something else: clear.
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Rather than deleting a breakpoint or watchpoint, you might prefer to disable it. This makes the breakpoint inoperative as if it had been deleted, but remembers the information on the breakpoint so that you can enable it again later.
You disable and enable breakpoints, watchpoints, and catchpoints with
the enable and disable commands, optionally specifying one
or more breakpoint numbers as arguments. Use info break or
info watch to print a list of breakpoints, watchpoints, and
catchpoints if you do not know which numbers to use.
A breakpoint, watchpoint, or catchpoint can have any of four different states of enablement:
break command starts out in this state.
tbreak command starts out in this state.
You can use the following commands to enable or disable breakpoints, watchpoints, and catchpoints:
disable [breakpoints]Disable the specified breakpoints--or all breakpoints, if none are
listed. A disabled breakpoint has no effect but is not forgotten. All
options such as ignore-counts, conditions and commands are remembered in
case the breakpoint is enabled again later. You may abbreviate
disable as dis.
enable [breakpoints]Enable the specified breakpoints (or all defined breakpoints). They become effective once again in stopping your program.
Except for a breakpoint set with tbreak (see section Setting breakpoints), breakpoints that you set are initially enabled;
subsequently, they become disabled or enabled only when you use one of
the commands above. (The command until can set and delete a
breakpoint of its own, but it does not change the state of your other
breakpoints; see Resuming Execution.)
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The simplest sort of breakpoint breaks every time your script reaches a specified place. You can also specify a condition for a breakpoint. A condition is just a BASH expression.
Break conditions can be specified when a breakpoint is set, by using
`if' in the arguments to the break command. See section Setting breakpoints. A breakpoint with a condition
evaluates the expression each time your script reaches it, and your
script stops only if the condition is true.
There is also a notion of a "one-time" breakpoint which gets deleted as soon as it is hit, so that that breakpoint is executed once only.
Conditions are also accepted for watchpoints; you may not need them, since a watchpoint is inspecting the value of an expression anyhow--but it might be simpler, say, to just set a watchpoint on a variable name, and specify a condition that tests whether the new value is an interesting one.
Break conditions can be specified when a breakpoint is set, by using
`if' in the arguments to the break command. See section Setting breakpoints. They can also be changed at any time
with the condition command.
condition bnum expressionSpecify expression as the break condition for breakpoint bnum. After you set a condition, breakpoint bnum stops your program only if the value of expression is true (nonzero).
condition bnumRemove the condition from breakpoint number bnum. It becomes an ordinary unconditional breakpoint.
BASH does
not actually evaluate expression at the time the condition
command (or a command that sets a breakpoint with a condition, like
break if …) is given, however.
Examples;
condition 1 x>5 # Stop on breakpoint 0 only if x>5 is true. condition 1 # Change that! Unconditinally stop on breakpoint 1. |
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Continuing means resuming program execution until your script completes normally. In contrast, stepping means executing just one more "step" of your script, where "step" may mean either one line of source code. Either when continuing or when stepping, your script may stop even sooner, due to a breakpoint or a signal.
| 4.4.2.1 Step (`step') | running the next statement (step) | |
| 4.4.2.2 Next (`next') | running the next statement skipping over functions (skip) | |
| 4.4.2.3 Finish (`finish') | running until the return of a function or "source" (finish) | |
| 4.4.2.4 Skip (`skip') | skipping the next statement (skip) | |
| 4.4.2.5 Continue (`continue') | continuing execution (continue) | |
| 4.4.2.6 Debug (`debug') | debugging into another program (debug) | |
| 4.4.2.7 Returning from a function, sourced file, or subshell (`return') | returning |
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stepContinue running your script until control reaches a different source
line, then stop it and return control to the BASH debugger. This command is
abbreviated s.
The step command only stops at the first instruction of a source
line. This prevents the multiple stops that could otherwise occur in
switch statements, for loops, etc. step continues
to stop if a function that has debugging information is called within
the line. In other words, step steps inside any functions
called within the line.
step [count]Continue running as in step, but do so count times. If a
breakpoint is reached, or a signal not related to stepping occurs before
count steps, stepping stops right away.
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next [count]Continue to the next source line in the current (innermost) stack frame.
This is similar to step, but function calls that appear within
the line of code are executed without stopping. Execution stops when
control reaches a different line of code at the original stack level
that was executing when you gave the next command. This command
is abbreviated n.
An argument count is a repeat count, as for step.
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finishContinue running until just after function returns. Currently,
the line shown on a return is the function header, unless the
return builtin function is executed in which case it is the
line number of the return function.
Contrast this with the return command (see section Returning from a function) and the quit (see section Quitting the BASH debugger).
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skip [count]Skip execution of the next source line.
This may be useful if you have an action that "fixes" existing code in
the script. The debug command internally uses the skip command
to skip over existing non-debugged invocation that was presumably just
run.
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continue [linespec]c [line-number]Resume program execution, at the address where your script last stopped; any breakpoints set at that address are bypassed. The optional argument linespec allows you to specify a linespec (a line number, function, or filename linenumber combination) to set. A one-time breakpoint is deleted when that breakpoint is reached. Should the program stop before that breakpoint is reached, for example, perhaps another breakpoint or watchpoint is reached first, in a listing of the breakpoints you will see this entry with the condition 9999 which indicates a one-time breakpoint.
To resume execution at a different place, you can use return
(see section Returning from a function) to go back to the
calling function or sourced script. If you are nested inside a
subshell, quit with a value for the number of subshells to
exit also functions like a return.
A typical technique for using stepping is to set a breakpoint (see section Breakpoints; watchpoints) at the beginning of the function or the section of your script where a problem is believed to lie, run your script until it stops at that breakpoint, and then step through the suspect area, examining the variables that are interesting, until you see the problem happen.
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debug [script-name]Debug into script-name. If no name is given the current source line is used. In either case the options are prepended to cause the debugger to run.
The nesting level of the debugger is saved inside environment variable
BASHDB_LEVEL. The debugger prompt indicates the level of nesting
by enclosing the history in that many nestings of <> symbols.
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returnreturnYou can cancel execution of a function call or a subshell with the
return command.
The return command does not resume execution; it leaves the
program stopped in the state that would exist if the function had just
returned. See also the quit command (Quitting the BASH debugger). In some situations return is similar to
quit: in particular when the script is not currenlty
inside in a function and the number of subshells in effect is 0, or
when a subshell count of 1 is given on the quit command.
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A signal is an asynchronous event that can happen in a program. The
operating system defines the possible kinds of signals, and gives each
kind a name and a number. For example, in Unix SIGINT is the
signal a program gets when you type an interrupt character (often
C-c); SIGALRM occurs when the alarm clock timer goes off
(which happens only if your program has requested an alarm).
Some signal handlers are installed and changed for the BASH debugger's
normal use: SIGDEBUG and SIGEXIT. SIGDEBUG is
used by the debugger to potentially stop your program before execution
of each statement occurs, and SIGEXIT is used to catch your
program just before it is set to leave so you have the option of
restarting the program with the same options (and not leave the
debugger) or let the program quit.
Signal handlers that the debugged script might have installed are
saved and called before the corresponding debugger handler. Thus, the
debugged program should work roughly in the same fashion as when it is
not debugged. However there are some call-stack variables which
inevitably will differ. To try to hedge this a little so the behaviour
is the same, the BASH debugger will modify arguments to the traps if it
finds one of the call-stack that change as a result of the debugger
being in place. In particluar $LINENO will get replaced with
${BASH_LINENO[0]}; also ${BASH_LINENO[0]} and
${BASH_SOURCE[0]} get replaced with
${BASH_LINENO[1]} and ${BASH_SOURCE[1]}
respectively.
The debugger also installs an interrupt handler SIGINT so that
errant programs can be interrupted and you can find out where the
program was when you interrupted it.
Some signals, including SIGALRM, are a normal part of the
functioning of your program. Others, such as SIGSEGV, indicate
errors; these signals are fatal (they kill your program immediately) if the
program has not specified in advance some other way to handle the signal.
SIGINT does not indicate an error in your program, but it is normally
fatal so it can carry out the purpose of the interrupt: to kill the program.
BASH has the ability to detect any occurrence of a signal in your program. You can tell BASH in advance what to do for each kind of signal.
Normally, BASH is set up to let the non-erroneous signals like
SIGALRM be silently passed to your program
(so as not to interfere with their role in the program's functioning)
but to stop your program immediately whenever an error signal happens.
You can change these settings with the handle command.
info signalsinfo handlePrint a table of all the kinds of signals and how BASH has been told to handle each one. You can use this to see the signal numbers of all the defined types of signals.
info handle is an alias for info signals.
handle signal keywords…Change the way BASH handles signal signal. signal can be the number of a signal or its name (with or without the `SIG' at the beginning); a list of signal numbers of the form `low-high'; or the word `all', meaning all the known signals. The keywords say what change to make.
The keywords allowed by the handle command can be abbreviated.
Their full names are:
stopBASH should stop your program when this signal happens. This implies
the print keyword as well.
nostopBASH should not stop your program when this signal happens. It may still print a message telling you that the signal has come in.
printBASH should print a message when this signal happens.
noprintBASH should not mention the occurrence of the signal at all.
stackBASH should print a stack trace when this signal happens.
nostackBASH should not print a stack trace when this signal occurs.
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| 4.5.1 Showing information about the program being debugged (`info') | Showing information about the program being debugged | |
| 4.5.2 Show information about the debugger (`show') | Show information about the debugger |
In addition to help, you can use the BASH commands info
and show to inquire about the state of your program, or the
state of BASH itself. Each command supports many topics of inquiry;
here we introduce each of them in the appropriate context. The
listings under info and under show in the Index point to
all the sub-commands. See section Command Index.
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This info command (abbreviated i) is for describing the state of
your program. For example, you can list the current $1, $2
parameters with info args, or list the breakpoints you have set
with info breakpoints or info watchpoints. You can get
a complete list of the info sub-commands with help
info.
info argsArgument variables (e.g. $1, $2, ...) of the current stack frame.
info breakpointsinfo displayinfo filesinfo functionsinfo lineinfo programinfo signalsinfo sourceinfo stackinfo terminalinfo variablesAll global and static variable names
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In contrast to info, show is for describing the state of
BASH itself. You can change most of the things you can
show, by using the related command set;
The distinction between info and show however is a bit
fuzzy and is kept here to try to follow the GDB interface.
For example, to list the arguments given to your script use
show args; info args does something different.
Here are three miscellaneous show subcommands, all of which are
exceptional in lacking corresponding set commands:
show versionShow what version of BASH is running. You should include this information in BASH bug-reports. If multiple versions of BASH are in use at your site, you may need to determine which version of BASH you are running; as BASH evolves, new commands are introduced, and old ones may wither away. Also, many system vendors ship variant versions of BASH, and there are variant versions of BASH in GNU/Linux distributions as well. The version number is the same as the one announced when you start BASH.
show copyingDisplay information about permission for copying BASH.
show linetraceShow if line tracing is enabled. See also Show position information as statements are executed (`set linetrace').
show loggingShow summary information of logging variables which can be set via
set logging. See also Logging output (`set logging', `set logging file'...).
show logging fileShow the current logging file.
show logging overwriteShow whether logging overwrites or appends to the log file.
show warrantyDisplay the GNU "NO WARRANTY" statement, or a warranty, if your version of the BASH debugger
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When your script has stopped, one thing you'll probably want to know is where it stopped and some idea of how it got there.
Each time your script performs a function call (either as part of a command substitution or not), or `source's a file, information about this action is saved. The call stack then is this a history of the calls that got you to the point that you are currently stopped at.
One of the stack frames is selected by the BASH debugger the BASH debugger particular, whenever you ask the BASH debugger a line number or location the value is found in the selected frame. There are special the BASH debugger are interested in. See section Selecting a frame.
When your program stops, BASH automatically selects the
currently executing frame and describes it briefly, similar to the
frame command.
| 4.6.1 Stack frames | ||
| 4.6.2 Backtraces (`where') | Backtraces (where) | |
| 4.6.3 Selecting a frame (`up', `down', `frame') | Selecting a frame (up, down, frame) | |
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The call stack is divided up into contiguous pieces called stack frames, or frames for short; each frame is the data associated with one call to one function. The frame contains the line number of the caller of the function, the source-file name that the line refers to a function name (which could be the built-in name "source")..
When your script is started, the stack has only one frame, that of the
function main. This is called the initial frame or the
outermost frame. Each time a function is called, a new frame is
made. Each time a function returns, the frame for that function invocation
is eliminated. If a function is recursive, there can be many frames for
the same function. The frame for the function in which execution is
actually occurring is called the innermost frame. This is the most
recently created of all the stack frames that still exist.
the BASH debugger assigns numbers to all existing stack frames, starting with zero for the innermost frame, one for the frame that called it, and so on upward. These numbers do not really exist in your script; they are assigned by the BASH debugger to give you a way of designating stack frames in the BASH debugger commands.
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A backtrace is essentially the same as the call stack: a summary of how your script got where it is. It shows one line per frame, for many frames, starting with the place that you sare stopped at (frame zero), followed by its caller (frame one), and on up the stack.
backtracebtwhereTPrint a backtrace of the entire stack: one line per frame for all frames in the stack.
backtrace nbt nwhere nT nSimilar, but print only the innermost n frames.
The names where and T are additional aliases for
backtrace.
Each line in the backtrace shows the frame number and the function name, the source file name and line number, as well as the function name.
Here is an example of a backtrace taken a program in the regression-tests `parm.sh'.
% ../bashdb -n -L .. parm.sh
Bourne-Again Shell Debugger, release 3.1-0.06
Copyright 2002, 2003, 2004, 2006 Rocky Bernstein
This is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
(./parm.sh:21):
21: fn1 5
bashdb<0> continue fn3
One-time breakpoint 1 set in file ./parm.sh, line 17.
fn2: testing 1 2 3
(./parm.sh:17):
17: fn3() {
bashdb<1> where
->0 in file `./parm.sh' at line 14
##1 fn3() called from file `./parm.sh' at line 14
##2 fn2("testing 1", "2 3") called from file `parm.sh' at line 5
##3 fn1("0") called from file `parm.sh' at line 9
##4 fn1("1") called from file `parm.sh' at line 9
##5 fn1("2") called from file `parm.sh' at line 9
##6 fn1("3") called from file `parm.sh' at line 9
##7 fn1("4") called from file `parm.sh' at line 9
##8 fn1("5") called from file `parm.sh' at line 21
##9 source("parm.sh") called from file `bashdb' at line 143
##10 main("-n", "-L", "..", "parm.sh") called from file `bashdb' at line 0
|
The display for "frame" zero isn't a frame at all, although it has
the same information minus a function name; it just indicates that
your script has stopped at the code for line 14
of ./parm.sh.
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Commands for listing source code in your script work on whichever stack frame is selected at the moment. Here are the commands for selecting a stack frame; all of them finish by printing a brief description of the stack frame just selected.
up nMove n frames up the stack. For positive numbers n, this advances toward the outermost frame, to higher frame numbers, to frames that have existed longer. n defaults to one.
down nMove n frames down the stack. For positive numbers n, this
advances toward the innermost frame, to lower frame numbers, to frames
that were created more recently. n defaults to one. You may
abbreviate down as do.
All of these commands end by printing two lines of output describing the frame. The first line shows the frame number, the function name, the arguments, and the source file and line number of execution in that frame. The second line shows the text of that source line.
For example:
|
After such a printout, the list command with no arguments
prints ten lines centered on the point of execution in the frame.
See section Printing source lines.
frame argsThe frame command allows you to move from one stack frame to
another, and to print the stack frame you select. args is the
the stack frame number. Without an argument, frame prints the
current stack frame.
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the BASH debugger can print parts of your script's source. When your script stops, the BASH debugger spontaneously prints the line where it stopped. Likewise, when you select a stack frame (see section Selecting a frame), the BASH debugger prints the line where execution in that frame has stopped. You can print other portions of source files by explicit command.
If you use the BASH debugger through its GNU Emacs interface, you may prefer to use Emacs facilities to view source; see Using the BASH debugger under GNU Emacs.
To print lines from a source file, use the list command
(abbreviated l). By default, ten lines are printed.
There are several ways to specify what part of the file you want to print.
Here are the forms of the list command most commonly used:
list linenuml linenumPrint lines centered around line number linenum in the current source file.
list functionl functionPrint the text of function.
listlPrint more lines. If the last lines printed were printed with a
list command, this prints lines following the last lines
printed; however, if the last line printed was a solitary line printed
as part of displaying a stack frame (see section Examining the Stack), this prints lines centered around that line.
list -l -Print lines just before the lines last printed.
By default, the BASH debugger prints ten source lines with any of these forms of
the list command.
You can change this using set listsize:
set listsize countMake the list command display count source lines (unless
the list argument explicitly specifies some other number).
show listsizeDisplay the number of lines that list prints.
Repeating a list command with RET discards the argument,
so it is equivalent to typing just list. This is more useful
than listing the same lines again. An exception is made for an
argument of `-'; that argument is preserved in repetition so that
each repetition moves up in the source file.
In general, the list command expects you to supply a
linespecs. Linespecs specify source lines; there are several ways
of writing them, but the effect is always to specify some source line.
Here is a complete description of the possible arguments for list:
list linespecPrint lines centered around the line specified by linespec.
list first incrementPrint increment lines starting from first
list firstPrint lines starting with first.
list -Print lines just before the lines last printed.
list .Print lines after where the script is stopped.
listAs described in the preceding table.
Here are the ways of specifying a single source line--all the kinds of linespec.
numberSpecifies line number of the current source file.
When a list command has two linespecs, this refers to
the same source file as the first linespec.
filename:numberSpecifies line number in the source file filename.
functionSpecifies the line that function function is listed on.
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There are two commands for searching through the current source file for a BASH extended pattern-matching expression.
forward bash-patternsearch bash-patternThe command `forward bash-pattern' checks each line,
starting with the one following the current line, for a match for
bash-pattern which is an extended bash pattern-matching
expression. It lists the line that is found. You can use the synonym
`search bash-pattern' or abbreviate the command name as
fo or /pat/.
reverse bash-patternThe command `reverse bash-pattern' checks each line, starting
with the one before the last line listed and going backward, for a match
for bash-pattern. It lists the line that is found. You can abbreviate
this command as rev or ?bash-pattern?.
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One way to examine string data in your script is with the print
command (abbreviated p). However a more versatile print command
is x; it can print variable and function definitions and can do
arithmetic computations. Finally, the most general method would be
via eval echo.
print exprUse print to display strings as you would from echo. And
as such, variable names to be substituted have to be preceded with a
dollar sign. As with echo, filename expansion, e.g. tilde expansion,
is performed on unquoted strings. So for example if you want to print
a *, you would write `print "*"', not `print *'. If you want
to have the special characters dollars sign appear, use a backslash.
bashdb<0> print the value of x is $x the value of x is 22 bashdb<1> p The home directory for root is ~root The home directory for root is /root bashdb<2> p '*** You may have won $$$ ***' *** You may have won $$$ *** bashdb<3> # Note the use of the single quotes. bashdb<3> # Compare what happens with double quotes or no quotes |
printpIf you omit expr, the BASH debugger displays the last expression again.
x variable1 [variable2...]x exprThis is a smarter, more versatile "print" command, and although sometimes
it might not be what you want, and you may want to resort to either
print or eval echo....
As with print, if you omit expr, the BASH debugger displays
the last expression again.
The x command first checks if expr is variable or a list
of variables delimited by spaces. If it is, the definition(s) and
value(s) of each printed via BASH's declare -p
command. This will show the variable's attributes such as if it is
read only or if it is an integer. If the variable is an array, that is
show and the array values are printed.
If instead expr is a function, the function definition is
printed via BASH's declare -f command. If expr
was neither a variable nor an expression, then we try to get a value
via let. And if this returns an error, as a last resort we call
print and give what it outputs.
Since let may be used internally and since (to my thinking)
let does funny things, the results may seem odd unless you
understand the sequence tried above and how let works. For
"example if the variable foo has value 5, then `x foo'
shows the definition of foo with value 5, and `x foo+5' prints 10
as expected. So far so good. However if foo is has the value
`alpha', `x foo+5' prints 5 because let has converted
the string `alpha' into the numeric value 0. So `p foo+5' will
simply print "foo+5"; if you want the value of "foo" substituted
inside a string, for example you expect "the value of foo is $foo"
to come out "the value of foo is 5", then the right command to use
is print rather than x, making sure you add the dollar
onto the beginning of the variable.
bashdb<0> examine x y
declare -- x="22"
declare -- y="23"
bashdb<1> examine x+y
45
bashdb<2> x fn1
fn1 ()
{
echo "fn1 here";
x=5;
fn3
}
bashdb<2> x FUNCNAME
declare -a FUNCNAME='([0]="_Dbg_cmd_x" [1]="_Dbg_cmdloop" [2]="_Dbg_debug_trap_handler" [3]="main")'
|
V [!][pattern]If you want to all list variables and values or a set of variables by pattern, use this command.
bashdb<0> V dq* dq_args="dq_*" dq_cmd="V" bashdb<1> V FUNCNAME FUNCNAME='([0]="_Dbg_cmd_list_variables" [1]="_Dbg_cmdloop" [2]="_Dbg_debug_trap_handler" [3]="main")' |
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The two most general commands and most "low-level" are eval
and shell.
evaleIn contrast to the commands of the last section the most general way
to examine data is through eval. But you do much more with
this; you can change the values of variables, since, you are just
evaluating BASH code.
If you expect output, you should arrange that in the command, such as
via echo or printf. For example, to print the value of
foo, you would type `e echo $foo'. This is bit longer than
`p $foo' or (when possible) `x foo'. However suppose you
wanted to find out how the builtin test operator `[' works with
the `-z' test condition. You could use eval to do this
such as `e [ -z "$foo"] && echo "yes"'.
shell command string!!If you need to execute occasional shell commands during your
debugging session, there is no need to leave or suspend the BASH debugger; you can
just use the shell command or its alias !!.
Invoke a shell to execute command string.
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cdSet working directory to directory for debugger and program being debugged. The change does not take effect for the program being debugged until the next time it is started.
pwdPrints the working directory as the program sees things.
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If you find that you want to print the value of an expression frequently (to see how it changes), you might want to add it to the automatic display list so that the BASH debugger evaluates a statement each time your program stops. Each expression added to the list is given a number to identify it; to remove an expression from the list, you specify that number. The automatic display looks like this:
2 (echo $x): 38 |
This display shows item numbers, expressions and their current values.
display exprAdd the expression expr to the list of expressions to display each time your program stops.
undisplay dnums…delete display dnums…Remove item numbers dnums from the list of expressions to display.
undisplay does not repeat if you press RET after using it.
(Otherwise you would just get the error `No display number …'.)
disable display dnums…Disable the display of item numbers dnums. A disabled display item is not printed automatically, but is not forgotten. It may be enabled again later.
enable display dnums…Enable display of item numbers dnums. It becomes effective once again in auto display of its expression, until you specify otherwise.
displayDisplay the current values of the expressions on the list, just as is done when your program stops.
info displayPrint the list of expressions previously set up to display automatically, each one with its item number, but without showing the values. This includes disabled expressions, which are marked as such. It also includes expressions which would not be displayed right now because they refer to automatic variables not currently available.
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You can alter the way BASH interacts with you in various ways given below.
| 4.13.1 Annotation Level (`set annotate') | Annotation Level (set annotate) | |
| 4.13.2 File basename (`set basename') | Show basenames of file names only (set basename) | |
| 4.13.3 Allow Debugging the debugger (`set debugger') | Allow debugging the debugger (set debugger) | |
| 4.13.4 Specifying a Script-File Association (`file') | Specifying a Script-File Associaton (set file) | |
| 4.13.5 Show position information as statements are executed (`set linetrace') | Show position information (set linetrace) | |
| 4.13.6 Logging output (`set logging', `set logging file'...) | Specifying where to write debugger output | |
| 4.13.7 Prompt (`set prompt', `show prompt') | Prompt (set prompt, show prompt) | |
| 4.13.8 Command editing (`set editing', `show editing') | Command editing (set editing, show editing) | |
| 4.13.9 Command Display (`set showcommand') | Command display (set showcommand) | |
| 4.13.10 Command history (`H', `history', `!') | Command history (history, !, H) | |
| 4.13.11 Command Completion (`complete') | Command completion (complete) |
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set annotate integerThe annotation level controls how much information the BASH debugger prints in its prompt; right new it just controls whether we show full filenames in output or the base part of the filename without path information. Level 0 is the normal, level 1 is for use when the BASH debugger is run as a subprocess of GNU Emacs of DDD, level 2 is the maximum annotation suitable for programs that control the BASH debugger.
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set basename [ on | 1 ]Source filenames are shown as the basename only. This is useful in running the regression tests.
set basename [ off | 0 ]Source filenames are shown as with their full path. This is the default.
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set debugger [ on | 1 ]Allow the possibility of debugging this debugger. Somewhat of an arcane thing to do. For gurus, and even he doesn't use it all that much.
set debugger [ off | 0 ]Don't allow debugging into the debugger. This is the default.
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Sometimes the BASH debugger gets confused about where to find the script
source file for the name reported to it by bash. To resolve relative
file names that bash supplies via BASH_SOURCE, the BASH debugger uses
the current working directory when the debugged script was started as
well as the current working directory now (which might be different
if a "cd" command was issued to change the working directory).
However somethimes this doesn't work and there is a way to override this.
file script-fileDirects the BASH debugger to use script-file whenever bash would have
it refers to the filename given in BASH_SOURCE. The filename
specified in BASH_SOURCE that gets overriden is shown when is
this command is issued.
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BASH has set -x tracing to show commands as they are
run. However missing from this is file and line position
information. So the debugger compensates here for what I think is
deficiency of BASH by providing this information. The downside
is that this tracing is slower than the built-in tracing of
BASH.
The status of whether line tracing is enabled can be show via
show linetrace.
set linetrace [ on | 1 ]Turn on line tracing.
set linetrace [ off | 0 ]Turn off line tracing.
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You may want to save the output of the debugger commands to a file. There are several commands to control the debuggers's logging.
set loggingset logging [ on | 1 ]Enable or Disable logging.
set logging file filenameChange the name of the current logfile. The default logfile is `bashdb.txt'.
set logging overwrite [ on | 1 ]By default, the debugger will append to the logfile. Set
overwrite if you want set logging on to overwrite the
logfile instead.
set logging redirect [ on | 1 ]By default, the debugger output will go to both the terminal and the
logfile. Set redirect if you want output to go only to the log
file.
show loggingShow the current values of the logging settings.
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The BASH debugger indicates its readiness to read a command by printing a string called the prompt. This string is normally:
bashdb${_Dbg_less}${#_Dbg_history[@]}${_Dbg_greater}$_Dbg_space
|
When variables inside the the prompt string are evaluated, the above becomes something like `bashdb<5>' if this is the fifth command executed or perhaps `bashdb<<2>>' if you have called the debugger from inside a debugger session and this is the second command inside the debugger session or perhaps `bashdb<(6)>' if you entered a subshell after the fifth command.
You can change the prompt string with the set prompt command,
although it is not normally advisable to do so without understanding
the implications. If you are using the DDD GUI, it changes the
changes the prompt and should not do so. In certain other
circumstances (such as writing a GUI like DDD), it may be is useful
to change the prompt.
Note: set prompt does not add a space for you after the
prompt you set. This allows you to set a prompt which ends in a space
or a prompt that does not. Furthermore due to a implementation
limitation (resulting from a limitation of the bash built-in function
"read"), to put a space at the end of the prompt use the
`$_Dbg_space' variable.
set prompt newpromptDirects the BASH debugger to use newprompt as its prompt string henceforth.
Warning: changing the prompt can DDD's ability to understand when the debugger is waiting for input.
show promptPrints a line of the form: `bashdb's prompt is: your-prompt'
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the BASH debugger reads its input commands through bash which uses via the
readline interface. This GNU library provides consistent
behavior for programs which provide a command line interface to the
user. Advantages are GNU Emacs-style or vi-style inline
editing of commands, csh-like history substitution, and a
storage and recall of command history across debugging sessions.
You may control the behavior of command line editing in BASH with the
command set.
set editingset editing [ on | 1 ]Enable command line editing (enabled by default).
set editing [ off | 0 ]Disable command line editing.
show editingShow whether command line editing is enabled.
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The debugger normally lists the line number and source line of the for the statement to be next executed. Often this line contains one expression or one statement and it is clear from this line what's going to happen. However BASH allows many expressions or statements to be put on a single source line; some lines contain several units of execution. Some examples of this behavior are listed below:
x=1; y=2; x=3 (( x > 5 )) && x=5 y=`echo *` |
In the first line of the example above, we have three assignment statements on a single line. In the second line of the example above we have a statement which gets run only if a condition tests true. And in the third line of the example above, we have a command that gets run and then the output of that is substituted in an assignemnt statement. If you were single stepping inside the debugger, each line might get listed more than once before each of the actions that might get performed. (In the case of the conditional statement, the line gets listed only once when the condition is false.)
In order to assist understanding where you are, the enhanced version
of BASH maintains a dynamic variable BASH_COMMAND that
contains piece of code next to be run (or is currently being run). The
debugger has arranged to save this and can display this information
or not. This is controlled by set showcommand.
set showcommand [auto | on | 1 | off | 0 ]controls whether or not to show the saved BASH_COMMAND for the
command next to be executed.
When the value is auto the following heuristic is used to
determine whether or not to display the saved BASH_COMMAND. If
the last time you stopped you were at the same place and the command
string has changed, then show the command. When the value on is
used, the debugger always shows BASH_COMMAND and when
off is used, the debugger nevers shows
BASH_COMMAND. Note that listing the text of the source line is
independent of whether or not the command is also listed.
Some examples:
set showcommand auto This is the default set showcommand on Always show the next command to be executed set showcommand off Never show the next command to be executed |
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The BASH debugger can keep track of the commands you type during your debugging sessions, so that you can be certain of precisely what happened. If the prompt has not been changed (see Prompt), the history number that will be in use next is by default listed in the debugger prompt. Invalid commands and history commands are not saved on the history stack.
H [start-number [end-number]]H [-count]![-]n:pYou can list what is in the history stack with H. Debugger
commands in ths history stack are listed from most recent to least recent.
If no start-number is given we start with the most recently
executed command and end with the first entry in the history stack.
If start-number is given, that history number is listed first. If
end-number is given, that history number is listed last. If a
single negative number is given list that many history commands.
An alternate form is !n:p or !-n:p where
n is an integer. If a minus sign is used, n is taken as
the count to go back from the end rather than as a absolute history
number. In contrast H, this form only prints a single
history item.
Some examples:
H List entire history H -2 List the last two history items !-2:p List a single history item starting at the same place as above H 5 List history from history number 5 to the begining (number 0) H 5 0 Same as above H 5 3 List history from history number 5 down to history number 3 !5:p List a single history item 5 |
history [[-]n]![-]nUse this command to reexecute a given history number. If no number is given, the last debugger command in the history is executed.
An alternate form is !n or !-n where
n is an integer.
If a minus sign is used in in either form, n is taken as the count to go back from the end rather than as a absolute history number.
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The complete args command lists all the possible
completions for the beginning of a command. We can also show
completions for set, show and info
subcommands. Use args to specify the beginning of the command
you want completed. For example:
complete d |
results in:
d debug delete disable display deleteall down |
And
complete set a |
results in:
set args set annotate |
This is intended for use by front-ends such as GNU Emacs and DDD.
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There are some front-ends that can use the BASH debugger as a back-end debugger.
| 5.1 Using the BASH debugger from GNU Emacs | ||
| 5.2 Using the BASH debugger from DDD |
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A special interface allows you to use GNU Emacs to view (and
edit) the source files for the program you are debugging with
the BASH debugger. However you must be using GNU Emacs version 21 or
greater. (M-x show-emacs-version inside GNU Emacs will
tell you what version you are running.)
To use this interface, use the command M-x bashdb in GNU Emacs. Give the executable file you want to debug as an argument. Make sure to use the version that comes with this package as this is newer than that supplied with GNU Emacs.
The bashdb command starts the BASH debugger as a subprocess of Emacs, with input and output through a newly created Emacs buffer.
Using the BASH debugger under Emacs is just like using the BASH debugger normally except for two things:
This applies both to the BASH debugger commands and their output, and to the input and output done by the program you are debugging.
This is useful because it means that you can copy the text of previous commands and input them again; you can even use parts of the output in this way.
All the facilities of GNU Emacs' Shell mode are available for interacting with your script. In particular, you can send signals the usual way--for example, C-c C-c for an interrupt, C-c C-z for a stop.
| 5.1.1 Commands from the GUD buffer | ||
| 5.1.2 Commands from the source script | ||
| 5.1.3 the BASH debugger from a GNU Emacs Shell |
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Each time the BASH debugger displays a stack frame, Emacs automatically finds the source file for that frame and puts an arrow (`=>') at the left margin of the current line. Emacs uses a separate buffer for source display, and splits the screen to show both your the BASH debugger session and the source.
Explicit the BASH debugger list or search commands still produce output as
usual, but you probably have no reason to use them from GNU Emacs.
Warning: If the directory where your script resides is not your current directory, it can be easy to confuse Emacs about the location of the source files, in which case the auxiliary display buffer does not appear to show your source. the BASH debugger can find programs by searching your environment's
PATHvariable, so the the BASH debugger input and output session proceeds normally; but Emacs does not get enough information back from the BASH debugger to locate the source files in this situation. To avoid this problem, either start the BASH debugger mode from the directory where your script resides, or specify an absolute file name when prompted for the M-x gdb argument.A similar confusion can result if you use the the BASH debugger
filecommand to switch to debugging a program in some other location, from an existing the BASH debugger buffer in Emacs.
By default, M-x bashdb calls the bash --debugger. If you
need to call the BASH debugger by a different name (for example, if you
keep several configurations around, with different names) you can set
the Emacs variable gud-bashdb-command-name; for example,
(setq gud-bashdb-command-name "bash --debugger") |
(preceded by M-: or ESC :, or typed in the *scratch* buffer, or
in your `.emacs' file) makes Emacs call the program named
"bash-debugger" instead.
In the the BASH debugger I/O buffer, you can use the Emacs commands listed
below in addition to the standard Shell mode commands. The I/O buffer
name name is usually *gud-script-name*, where
script-name is the name of the script you are debugging.
Many of the commands listed below are also bound to a second key sequence which also can be used in the also be used in the source script. These are listed in Commands from the source script.
Describe the features of Emacs' the BASH debugger Mode.
Execute until exit from the selected stack frame. The Same as the BASH debugger
finish command. The GNU Emacs command name is
gud-finish and C-x C-a f C-f is an alternate binding
which also can be used in the source script. See section Finish (`finish').
Resynchronize the current position with the source window. The
GNU Emacs command name is gud-refresh and C-x C-a
C-l is an alternate binding which also can be used in the source script.
Execute to next source line in this function, skipping all function
calls. Same as the BASH debugger next command. The GNU Emacs
command name is gud-next and C-x C-a n is an
alternate binding which also can be used in the source script. See section Next (`next').
With a numeric argument, run that many times. See (Emacs)Arguments section `Numeric Arguments' in The GNU Emacs Manual.
Continue execution of your script Same as the BASH debugger continue
command. The GNU Emacs command name is gud-cont and
C-x C-a C-r is an alternate binding which also can be used in the
source script. See Continue (`continue').
Step one source line. Same as the BASH debugger step command. The
GNU Emacs command name is gud-step and C-x C-a C-s
is an alternate binding which can be used in the source
script. See section Step (`step').
With a numeric argument, run that many times. See (Emacs)Arguments section `Numeric Arguments' in The GNU Emacs Manual.
Go down a stack frame. Same as the BASH debugger down.
With a numeric argument, go down that many stack frames.
See (Emacs)Arguments section `Numeric Arguments' in The GNU Emacs Manual.
The GNU Emacs command name is
gud-down and C-x C-a > is an alternate binding
which can be used in the source script.
Go up a stack frame. With a numeric argument, go up that many
stack frames. Same the BASH debugger up command.
See (Emacs)Arguments section `Numeric Arguments' in The GNU Emacs Manual.
The GNU Emacs command name is
gud-up and C-x C-a < is an alternate binding
which can be used in the source script.
Shows argument variables (e.g. $1, $2) of the current
stack frame. Same as the BASH debugger info args command. The
GNU Emacs command name is gud-args and C-x C-a a is
an alternate binding which also can be used in the source script.
Restart or run the script. Same as the BASH debugger run command. The
GNU Emacs command name is gud-finish and C-x C-a R
is an alternate binding which also can be used in the source script.
Show stack trace. Same as the BASH debugger where command. The
GNU Emacs command name is gud-where and C-x C-a T is
an alternate binding which can be used in the source
script. See section Backtraces (`where').
In any source file, the Emacs command C-x SPC (gud-break)
tells the BASH debugger to set a breakpoint on the source line point is on.
If you accidentally delete the source-display buffer, an easy way to get
it back is to type the command frame in the the BASH debugger buffer, to
request a frame display; when you run under Emacs, this recreates
the source buffer if necessary to show you the context of the current
frame.
The source files displayed in Emacs are in ordinary Emacs buffers which are visiting the source files in the usual way. You can edit the files with these buffers if you wish; but keep in mind that the BASH debugger communicates with Emacs in terms of line numbers. If you add or delete lines from the text, the line numbers that the BASH debugger knows cease to correspond properly with the code.
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tells the BASH debugger to set a breakpoint on the source
line point is on. (gud-break)
gud-linetrace
Restart or run the script. Same as the BASH debugger run command. The
GNU Emacs command name is gud-finish. In the corresponding
I/O buffer, C-c R is an alternate binding.
Show stack trace. Same as the BASH debugger where command. In the
corresponding I/O buffer, C-c T is an alternate
binding. See section Backtraces (`where').
Go up a stack frame. With a numeric argument, go up that many
stack frames. Same the BASH debugger up command.
See (Emacs)Arguments section `Numeric Arguments' in The GNU Emacs Manual.
The GNU Emacs command name is gud-up. In the corresponding
I/O buffer, C-c < is an alternate binding.
Go down a stack frame. Same as the BASH debugger down.
With a numeric argument, go down that many stack frames.
See (Emacs)Arguments section `Numeric Arguments' in The GNU Emacs Manual.
The GNU Emacs command name is gud-down. In the
corresponding I/O buffer, C-c > is an alternate binding.
gud-tbreak
Step one source line. Same as the BASH debugger step
command. See section Step (`step').
With a numeric argument, run that many times. See (Emacs)Arguments section `Numeric Arguments' in The GNU Emacs Manual.
The GNU Emacs command name is gud-step. In the
corresponding I/O buffer, C-c C-s is an alternate binding.
gud-statement
Restart or run the script. Same as the BASH debugger run command. The
GNU Emacs command name is gud-run. In the corresponding I/O
buffer, C-c R is an alternate binding.
Delete breakpoint. gud-remove
gud-print
Execute to next source line in this function, skipping all function
calls. Same as the BASH debugger next command. With a numeric
argument, run that many times. See (Emacs)Arguments section `Numeric Arguments' in The GNU Emacs Manual.
The GNU Emacs command name is gud-next. In the
corresponding I/O buffer, C-c C-n is an alternate binding.
gud-finish
Continue execution of your script Same as the BASH debugger continue
command. The GNU Emacs command name is gud-cont. In the
corresponding I/O buffer, C-c C-r is an alternate binding. See
Continue (`continue').
gud-break
gud-args
Shows argument variables (e.g. $1, $2) of the current
stack frame. Same as the BASH debugger info args command. The
GNU Emacs command name is gud-args. In the corresponding
I/O buffer, C-c a is an alternate binding which also can be
used in the source script.
Move to current position in this source window. The GNU Emacs
command name is gud-refresh. In the corresponding I/O buffer,
C-c C-l is an alternate binding.
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It is also possible in GNU emacs to use a regular ("comint") shell
and set a mode to watch for the BASH debugger prompts. To do this, in Emacs
issue the command (from M-x) turn-on-bashdbtrack. There is some
overhead involved in scanning output, so if you are not debugging bash
programs you probably want to turn this off which can be done via the
M-x turn-off-bashdbtrack command.
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the BASH debugger support is rather new in DDD. As a programming language, the BASH debugger is not feature rich: there are no record structures or hash tables (yet), no pointers, package variable scoping or methods. So much of the data display and visualization features of DDD are disabled.
As with any scripting or interpreted language (e.g. Perl), one can't step by a single machine-language instruction. So the ddd Stepi/Nexti commands are disabled.
Some BASH settings are essential for DDD to work correctly. These settings with their correct values are:
set annotate 1 set prompt set prompt bashdb$_Dbg_less$_Dbg_greater$_Dbg_space |
DDD sets these values automatically when invoking BASH; if these values are changed, there may be some malfunctions.
Pay special attention when the prompt has extra angle brackets (a nested shell) or has any parenthesis (is in a subshell). Quitting may merely exit out of one of these nested (sub)shells rather than leave the program.
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Your bug reports play an essential role in making the BASH debugger reliable.
Reporting a bug may help you by bringing a solution to your problem, or it may not. But in any case the principal function of a bug report is to help the entire community by making the next version of the BASH debugger work better. Bug reports are your contribution to the maintenance of the BASH debugger.
In order for a bug report to serve its purpose, you must include the information that enables us to fix the bug.
| 6.1 Have you found a bug? | ||
| 6.2 How to report bugs |
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If you are not sure whether you have found a bug, here are some guidelines:
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Bug reports can sent via the sourceforge bug tracking mechansim at http://sourceforge.net/tracker/?group_id=61395&atid=497159. Of course patches are very much welcome too. Those can also be sent via the same mechanism.
The fundamental principle of reporting bugs usefully is this: report all the facts. If you are not sure whether to state a fact or leave it out, state it!
Often people omit facts because they think they know what causes the problem and assume that some details do not matter. Thus, you might assume that the name of the variable you use in an example does not matter. Well, probably it does not, but one cannot be sure. Perhaps the bug is a stray memory reference which happens to fetch from the location where that name is stored in memory; perhaps, if the name were different, the contents of that location would fool the debugger into doing the right thing despite the bug. Play it safe and give a specific, complete example. That is the easiest thing for you to do, and the most helpful.
Keep in mind that the purpose of a bug report is to enable us to fix the bug. It may be that the bug has been reported previously, but neither you nor we can know that unless your bug report is complete and self-contained.
Sometimes people give a few sketchy facts and ask, "Does this ring a bell?" Those bug reports are useless, and we urge everyone to refuse to respond to them except to chide the sender to report bugs properly.
To enable us to fix the bug, you should include all these things:
version
command.
Without this, we will not know whether there is any point in looking for the bug in the current version of the BASH debugger.
If we were to try to guess the arguments, we would probably guess wrong and then we might not encounter the bug.
Of course, if the bug is that the BASH debugger gets a fatal signal, then we will certainly notice it. But if the bug is incorrect output, we might not notice unless it is glaringly wrong. You might as well not give us a chance to make a mistake.
Even if the problem you experience is a fatal signal, you should still say so explicitly. Suppose something strange is going on, such as, your copy of the BASH debugger is out of synch, or you have encountered a bug in the C library on your system. (This has happened!) Your copy might crash and ours would not. If you told us to expect a crash, then when ours fails to crash, we would know that the bug was not happening for us. If you had not told us to expect a crash, then we would not be able to draw any conclusion from our observations.
The line numbers in our development sources will not match those in your sources. Your line numbers would convey no useful information to us.
Here are some things that are not necessary:
Often people who encounter a bug spend a lot of time investigating which changes to the input file will make the bug go away and which changes will not affect it.
This is often time consuming and not very useful, because the way we will find the bug is by running a single example under the debugger with breakpoints, not by pure deduction from a series of examples. We recommend that you save your time for something else.
Of course, if you can find a simpler example to report instead of the original one, that is a convenience for us. Errors in the output will be easier to spot, running under the debugger will take less time, and so on.
However, simplification is not vital; if you do not want to do this, report the bug anyway and send us the entire test case you used.
A patch for the bug does help us if it is a good one. But do not omit the necessary information, such as the test case, on the assumption that a patch is all we need. We might see problems with your patch and decide to fix the problem another way, or we might not understand it at all.
Sometimes with a program as complicated as the BASH debugger it is very hard to construct an example that will make the program follow a certain path through the code. If you do not send us the example, we will not be able to construct one, so we will not be able to verify that the bug is fixed.
And if we cannot understand what bug you are trying to fix, or why your patch should be an improvement, we will not install it. A test case will help us to understand.
Such guesses are usually wrong. Even we cannot guess right about such things without first using the debugger to find the facts.
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The suggestion for a debugger for a Bourne-like shell came from the book "Learning the Korn Shell", by Bill Rosenblatt Copyright (C) 1993 by O'Reilly and Associates, Inc. Others such as Cigy Cyriac, Chet Ramey, Rocky Bernstein, and Gary V. Vaughan expanded and improved on that.
However Bourne-Shell debuggers rely on a signal mechanism
(SIGDEBUG) to call a debugger routine. In the Korn shell as
well as BASH in versions prior to 2.05, there was a fundamental
flaw: the routine that you registered in the trap, got called
after the statement was executed. It takes little imagination
to realize that this is a bit too late to find and correct errors,
especially if the offending command happens to do serious damage like
remove filesystems or reboot a server. As a horrible hack, these
debuggers added one to the line number that was just executed on the
wishful thinking that this would then be the line of next statement to
execute. Sometimes this was correct, but it was too often wrong, such
as in loops and conditionals, comments, or commands that are continued
on the next line.
Another failing of these debuggers was the inability to debug into functions or into sourced files, provide a stack trace, dynamically skip a statement to be run, unconditionally trace into a function or subshell, or stop when a subroutine, sourced file, or subshell completed. In truth, the crux of the problem lay in debugging support in BASH. Given that there was limited bash debugging support, it is not surprising that these debuggers could not do any of the things listed above and could debug only a single shell in a single source file: lines could be listed only from a single text, breakpoints were set into the text which was in fact a copy of the script name prepended with debugger routines.
In version 2.04 of BASH, Rocky Bernstein started hacking on BASH to
add call-stack information, source file information, allow for
debugging into functions and for reporting line numbers in functions
as relative to the file rather than the beginning of a function whose
origin line number was not accessible from BASH. He started changing
the user commands in bashdb to be like other more-advanced debuggers,
in particular perl5db and gdb. However he gave up on
this project when realizing that stopping before a line was crucial. A
patch for this was nontrivial and wildly changed
semantics. Furthermore the chance of getting his other patches into
BASH was was not going to happen in version 2.04.
In version 2.05, the fundamental necessary change to the semantics of
SIGDEBUG trap handling (suggested at least two years earlier)
was made. Also, version 2.05 changed the line-number reporting in a
function to be relative to the beginning of the file rather than the
beginning of a function--sometimes. Rocky then picked up where he
left off and this then became this debugger. A complete rewrite of the
debugger, some of which started in 2.04 was undertaken. Debugger
internals were changed to support multiple file names, save and
restore the calling environment (such as variables $1 and
$?) and install debugger signal handlers. Work was also done on
the BASH in conjunction with the debugger to save stack trace
information, provide a means for stopping after a routine finished,
debugging into a subshell and so on. And a number of changes were made
to BASH just to improve the accuracy of the line number reporting
which is crucial in a debugger.
This documentation was modified from the GNU Debugger (GDB) Reference manual.
Additions to this section are particularly welcome. If you or your friends (or enemies, to be evenhanded) have been unfairly omitted from this list, we would like to add your names!
The following have contributed directly or indrectly to bashdb:
Rocky Bernstein (initial full-featured bashdb with stack tracing and multi-file support)
Masatake YAMATO (help to merge Rocky's hack to the official bash source tree)
Bill Rosenblatt (kshdb), Michael Loukides (kshdb), Cigy Cyriac (proto bashdb), Chet Ramey (proto bashdb), and Gary V. Vaughan (proto bashdb).
Authors of per5ldb:
Ray Lischner, Johan Vromans, and Ilya Zakharevich.
Authors of GDB:
Richard Stallman, Andrew Cagney, Jim Blandy, Jason Molenda, Stan Shebs, Fred Fish, Stu Grossman, John Gilmore, Jim Kingdon, and Randy Smith (to name just a few).
Authors of GUD:
Eric S. Raymond.
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Version 2, June 1991
Copyright © 1989, 1991 Free Software Foundation, Inc. 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. |
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The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software--to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too.
When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.
To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it.
For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights.
We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software.
Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations.
Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all.
The precise terms and conditions for copying, distribution and modification follow.
TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
Activities other than copying, distribution and modification are not covered by this License; they are outside its scope. The act of running the Program is not restricted, and the output from the Program is covered only if its contents constitute a work based on the Program (independent of having been made by running the Program). Whether that is true depends on what the Program does.
You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection in exchange for a fee.
These requirements apply to the modified work as a whole. If identifiable sections of that work are not derived from the Program, and can be reasonably considered independent and separate works in themselves, then this License, and its terms, do not apply to those sections when you distribute them as separate works. But when you distribute the same sections as part of a whole which is a work based on the Program, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it.
Thus, it is not the intent of this section to claim rights or contest your rights to work written entirely by you; rather, the intent is to exercise the right to control the distribution of derivative or collective works based on the Program.
In addition, mere aggregation of another work not based on the Program with the Program (or with a work based on the Program) on a volume of a storage or distribution medium does not bring the other work under the scope of this License.
The source code for a work means the preferred form of the work for making modifications to it. For an executable work, complete source code means all the source code for all modules it contains, plus any associated interface definition files, plus the scripts used to control compilation and installation of the executable. However, as a special exception, the source code distributed need not include anything that is normally distributed (in either source or binary form) with the major components (compiler, kernel, and so on) of the operating system on which the executable runs, unless that component itself accompanies the executable.
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This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this License.
Each version is given a distinguishing version number. If the Program specifies a version number of this License which applies to it and "any later version", you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of this License, you may choose any version ever published by the Free Software Foundation.
NO WARRANTY
END OF TERMS AND CONDITIONS
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If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.
To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the "copyright" line and a pointer to where the full notice is found.
one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. |
Also add information on how to contact you by electronic and paper mail.
If the program is interactive, make it output a short notice like this when it starts in an interactive mode:
Gnomovision version 69, Copyright (C) year name of author Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'. This is free software, and you are welcome to redistribute it under certain conditions; type `show c' for details. |
The hypothetical commands `show w' and `show c' should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than `show w' and `show c'; they could even be mouse-clicks or menu items--whatever suits your program.
You should also get your employer (if you work as a programmer) or your school, if any, to sign a "copyright disclaimer" for the program, if necessary. Here is a sample; alter the names:
Yoyodyne, Inc., hereby disclaims all copyright interest in the program `Gnomovision' (which makes passes at compilers) written by James Hacker. signature of Ty Coon, 1 April 1989 Ty Coon, President of Vice |
This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Library General Public License instead of this License.
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Version 1.1, March 2000
Copyright (C) 2000 Free Software Foundation, Inc. 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. |
The purpose of this License is to make a manual, textbook, or other written document "free" in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.
This License is a kind of "copyleft", which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.
We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.
This License applies to any manual or other work that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. The "Document", below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as "you."
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The "Invariant Sections" are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License.
The "Cover Texts" are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License.
A "Transparent" copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, whose contents can be viewed and edited directly and straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup has been designed to thwart or discourage subsequent modification by readers is not Transparent. A copy that is not "Transparent" is called "Opaque."
Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML designed for human modification. Opaque formats include PostScript, PDF, proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML produced by some word processors for output purposes only.
The "Title Page" means, for a printed book, the title page itself,
plus such following pages as are needed to hold, legibly, the material
this License requires to appear in the title page. For works in
formats which do not have any title page as such, "Title Page" means
the text near the most prominent appearance of the work's title,
preceding the beginning of the body of the text.
You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.
You may also lend copies, under the same conditions stated above, and
you may publicly display copies.
If you publish printed copies of the Document numbering more than 100, and the Document's license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.
If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.
If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a publicly-accessible computer-network location containing a complete Transparent copy of the Document, free of added material, which the general network-using public has access to download anonymously at no charge using public-standard network protocols. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.
It is requested, but not required, that you contact the authors of the
Document well before redistributing any large number of copies, to give
them a chance to provide you with an updated version of the Document.
You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:
A. Use in the Title Page (and on the covers, if any) a title distinct
from that of the Document, and from those of previous versions
(which should, if there were any, be listed in the History section
of the Document). You may use the same title as a previous version
if the original publisher of that version gives permission.
B. List on the Title Page, as authors, one or more persons or entities
responsible for authorship of the modifications in the Modified
Version, together with at least five of the principal authors of the
Document (all of its principal authors, if it has less than five).
C. State on the Title page the name of the publisher of the
Modified Version, as the publisher.
D. Preserve all the copyright notices of the Document.
E. Add an appropriate copyright notice for your modifications
adjacent to the other copyright notices.
F. Include, immediately after the copyright notices, a license notice
giving the public permission to use the Modified Version under the
terms of this License, in the form shown in the Addendum below.
G. Preserve in that license notice the full lists of Invariant Sections
and required Cover Texts given in the Document's license notice.
H. Include an unaltered copy of this License.
I. Preserve the section entitled "History", and its title, and add to
it an item stating at least the title, year, new authors, and
publisher of the Modified Version as given on the Title Page. If
there is no section entitled "History" in the Document, create one
stating the title, year, authors, and publisher of the Document as
given on its Title Page, then add an item describing the Modified
Version as stated in the previous sentence.
J. Preserve the network location, if any, given in the Document for
public access to a Transparent copy of the Document, and likewise
the network locations given in the Document for previous versions
it was based on. These may be placed in the "History" section.
You may omit a network location for a work that was published at
least four years before the Document itself, or if the original
publisher of the version it refers to gives permission.
K. In any section entitled "Acknowledgements" or "Dedications",
preserve the section's title, and preserve in the section all the
substance and tone of each of the contributor acknowledgements
and/or dedications given therein.
L. Preserve all the Invariant Sections of the Document,
unaltered in their text and in their titles. Section numbers
or the equivalent are not considered part of the section titles.
M. Delete any section entitled "Endorsements." Such a section
may not be included in the Modified Version.
N. Do not retitle any existing section as "Endorsements"
or to conflict in title with any Invariant Section.
If the Modified Version includes new front-matter sections or
appendices that qualify as Secondary Sections and contain no material
copied from the Document, you may at your option designate some or all
of these sections as invariant. To do this, add their titles to the
list of Invariant Sections in the Modified Version's license notice.
These titles must be distinct from any other section titles.
You may add a section entitled "Endorsements", provided it contains nothing but endorsements of your Modified Version by various parties-for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.
You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.
The author(s) and publisher(s) of the Document do not by this License
give permission to use their names for publicity for or to assert or
imply endorsement of any Modified Version.
You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice.
The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.
In the combination, you must combine any sections entitled "History"
in the various original documents, forming one section entitled
"History"; likewise combine any sections entitled "Acknowledgements",
and any sections entitled "Dedications." You must delete all sections
entitled "Endorsements."
You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.
You may extract a single document from such a collection, and distribute
it individually under this License, provided you insert a copy of this
License into the extracted document, and follow this License in all
other respects regarding verbatim copying of that document.
A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, does not as a whole count as a Modified Version of the Document, provided no compilation copyright is claimed for the compilation. Such a compilation is called an "aggregate", and this License does not apply to the other self-contained works thus compiled with the Document, on account of their being thus compiled, if they are not themselves derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these
copies of the Document, then if the Document is less than one quarter
of the entire aggregate, the Document's Cover Texts may be placed on
covers that surround only the Document within the aggregate.
Otherwise they must appear on covers around the whole aggregate.
Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section 4.
Replacing Invariant Sections with translations requires special
permission from their copyright holders, but you may include
translations of some or all Invariant Sections in addition to the
original versions of these Invariant Sections. You may include a
translation of this License provided that you also include the
original English version of this License. In case of a disagreement
between the translation and the original English version of this
License, the original English version will prevail.
You may not copy, modify, sublicense, or distribute the Document except
as expressly provided for under this License. Any other attempt to
copy, modify, sublicense or distribute the Document is void, and will
automatically terminate your rights under this License. However,
parties who have received copies, or rights, from you under this
License will not have their licenses terminated so long as such
parties remain in full compliance.
The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.
Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License "or any later version" applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.
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To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:
Copyright (C) year your name. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being list their titles, with the Front-Cover Texts being list, and with the Back-Cover Texts being list. A copy of the license is included in the section entitled "GNU Free Documentation License." |
If you have no Invariant Sections, write "with no Invariant Sections" instead of saying which ones are invariant. If you have no Front-Cover Texts, write "no Front-Cover Texts" instead of "Front-Cover Texts being list"; likewise for Back-Cover Texts.
If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.
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The DJGPP port of the BASH debugger limitations of file names imposed by DOS filesystems.
On
DOS/Windows systems, the home directory is the one pointed to by the
HOME environment variable.
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