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Bash Debugger

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BASH Debugging

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Bashdb is nice debugger for bash, but usually it is not installed by default. You either need to install it from source using version 3 if you have bash 3 and version 4 if you have bash 4.1 or bash 4.2. See BASH with Debugger and Improved Debug Support and Error Handling or to the link to the tarball. Installation consist of three commands

cd bashdb-3.x... # <-- put name of release for 3.x...
./configure      # use --with-bash-src to speed up bash debugging
make && make check 
su -c 'make install' # should run as root
If those steps run OK, you should have debugger available in /usr/local/bin. You can use debugger even without installation. In this case you need to be in the directory you untared it and use the option “-L .”:
bash -L ./bashdb script-to-be-debugged options-to-debugged-program

If bashdb has been installed you don’t need to use option “-L .” Instead you would type simply

bashdb script-to-be-debugged options-to-debugged-program

I would recommend to check syntax of the bash script before using the debugger using option "-n", for example 

bash -n your_script.sh

Let's summarize the essentials of the debugger invocation:

  1. type bash --debugger script-name  or bashdb script-name to start the BASH debugger. 
  2. type bashdb -c command string to run a command or one-liner under the debugger.
  3. Or type bashdb -h  to get help about options available (bashdb --help   works too)

Two useful commands are n (next) - next step and p (print) -- print the variable or expression. Type quit or C-d inside the debugger to exit. Other way to terminate the debugger is to use the kill command. kill -9 can be used in cases where quit doesn't work.

Once inside the BASH debugger, you can always ask it for information on its commands, using the command help. You can use help (abbreviated h) with no arguments to display a short list of named classes of commands: >
bashdb<0> help
Available commands:
  /          debug    enable   help     next     show    step-      untrace
  alias      delete   eval     history  print    signal  tbreak     up     
  break      disable  examine  info     pwd      skip    trace      watch  
  commands   display  file     kill     quit     source  tty        where  
  condition  down     frame    list     restart  step    unalias  
  continue   edit     handle   load     set      step+   undisplay

Basdb documentation has several examples on how to use bashdb. See  Summary of the BASH Debugger

Dynamic activation from scripts

You can activate the debugger within the script. you can make an explicit call to the debugger in your script

_Dbg_debugger 

Here is an example:

  for ((i=1; i<=10; i++)) ; 
        (( 5 == i )) && { _Dbg_debugger }
        date=$(date)
        echo "$date"
        sleep 2
  done 

You can also turn on and off line tracing with _Dbg_linetrace_on

Frontends

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.

Getting the bashdb

bashdb is available as a source package in Debian, Fedora and OpenSuse. The Ubuntu repository contains a package for bashdb too.

Please note that for bash 4.x you need   version of bashdb, version 4.0.x, while for bash 3.x. version of bashdb should be 3.0.x.

Tarball with debugger is downloadable from Sourceforge:

https://sourceforge.net/project/showfiles.php?group_id=61395

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Last modified: March 12, 2019