How can I debug the Bourne Shell with gdb?

Question

I built a toolchain script to prepare a Linux build environment. The script can be found here: https://github.com/mynameismevin/prometheus/blob/toolchain/ptool-make.sh

The script runs perfectly until after the Perl section around line 416. After Perl is done, when it goes to unzip sed, it complains with this error:

tar (child): sed-4.2.2.tar.bz2: Cannot open: No such file or directory
tar (child): Error is not recoverable: exiting now
tar: Child returned status 2
tar: Error is not recoverable: exiting now

However, if I run the sections by hand, it completes without errors. If I split the script into ptool-make1.sh (which ends at Perl) and ptool-make2.sh (which starts at sed) and run them sequentially then they both complete without any issues at all. At this point, I assert the issue isn't with the script, and I would like to debug the shell to see if it's an issue with the shell.

Here are some useful configurations:

user@ubuntu:~$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=14.04
DISTRIB_CODENAME=trusty
DISTRIB_DESCRIPTION="Ubuntu 14.04.2 LTS"
user@ubuntu:~$ bash --version
GNU bash, version 4.3.11(1)-release (x86_64-pc-linux-gnu)
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
user@ubuntu:~$ ls -lh $(which bash)
-rwxr-xr-x 1 root root 998K Oct  7  2014 /bin/bash

I don't think Ubuntu bash comes with debugging symbols, so I would assume I would have to recompile to include those?

How would I use gdb to debug the shell when I run a script? Or how would I have the shell log to a file while the script runs so I can open it with gdb after it's done? I know how to debug a shell script, I don't want to debug the script, I want to debug the shell.

Edit: It doesn't look like Ubuntu bash comes with debugging symbols out of the box. Reading symbols from bash...(no debugging symbols found)...done.

Edit: $PROMETHEUS is set in my root shell. At the end of Perl cd .. results in the same results a cd $PROMETHEUS/sources/.

Answer 1

Shells come with their own debugging tools. The most simple is running them with -x (bash -x ...script...) which will print each command after variable expansion but before it is executed. That's usually enough to determine the problem.

For more ideas, see How to debug a bash script?

You should also consider to write helper functions to reduce the size of the script to just a few lines. You could move special options to configure or post-build steps into extra files and run them from the helper function if they exist.

Looking at the code, it seems that this line is the culrit:

cd $PROMETHEUS/sources/

everywhere else, you just use cd ... If PROMETHEUS isn't defined (the script doesn't define it, that becomes cd /sources/ which should also fail but doesn't abort your script. Try

cd $PROMETHEUS/sources/ || exit 1

instead. Also #!/bin/bash -u might be useful (abort on undefined variables).

Lastly, you can use pushd and popd to navigate the folders.