make a shell command show a call trace on failure

traceback

#!/bin/sh

:<<'=cut'

=head1 NAME

traceback - make a shell command show a call trace on failure

=head1 SYNOPSIS

  ln -s /path/to/traceback bin/problematiccommand

=head1 DESCRIPTION

B<traceback> is an aid
for debugging an error message from a shell script which is
too uninformative and/or comes from an unknown source.
As long as you know which individual command has an error,
and as long as it properly sets the errorlevel on error,
you can obtain a traceback when the error happens to see
what was going on in the calling script's little mind.

=head1 USAGE EXAMPLES

  sh$ mkdir $HOME/bin/traceback

  sh$ PATH=$HOME/bin/traceback:$PATH

  sh$ ln -s /path/to/traceback $HOME/bin/traceback/sed

  sh$ hash -r sed

  sh$ type sed
  sed is hashed (/home/you/bin/traceback/sed)

  sh$ sed 's%foo/bar/'
  /bin/sed: -e expression #1, char 9: unterminated `s' command
  traceback for process 1163:
  * 1163 /bin/sh /home/you/bin/traceback/sed s%foo/bar/ (cwd: /tmp)
  * 4245 /bin/bash (cwd: /home/you/project)
  * 4239 SCREEN -e ^Ll (cwd: denied)

... or, perhaps more realistically

  bash$ cd problematicproject

  bash$ ./problematicscript
  /usr/bin/expr: non-numeric argument
  ./problematicscript: catastrophic failure, aborting at line 93845

  bash$ !? fsck
  !?: event not found

  bash$ mkdir bin

  bash$ ln -s /usr/local/bin/traceback bin/expr

  bash$ PATH=`pwd`/bin:$PATH ./problematicscript
  /usr/bin/expr: non-numeric argument
  traceback for process 3908:
  3908 /bin/sh /home/you/work/problematicproject/bin/expr 1 + var (cwd: ...)
  3905 /bin/sh /home/you/bin/calculatestuff /tmp/subscript.7Fg49Ab (cwd: ...)
  3901 /bin/sh subscript fortytwo (cwd: /home/you/work/problematicproject)
  3887 /bin/sh problematicscript
  1122 -bash (cwd: /home/you/work/problematicproject)
  ./problematicscript: catastrophic failure, aborting at line 93845


=head1 PORTABILITY

This relies on specific L<ps(1)> options,
so is not portable.
Currently, this is Linux only
(or possibly even Debian only).

Also, requires L<lsof(1)>.


=head1 AUTHOR

tripleee
L<tripleee@users.noreply.github.com>


=head1 LICENSE

There is no explicit license at this point in time.
If it bothers you, get in touch and I'll add the necessary
copyright notices etc.
My intent is to distribute this under the
BSD license (without advertising clause, of course).


=head1 SEE ALSO

L<sh(1)>,
L<python(1)>;
L<ps(1)>,
L<lsof(1)>

=cut


cmd=$(basename "$0")
pth=$(type -a -p "$cmd" | fgrep -vx "$0" | head -n 1)
"$pth" "$@"
rc=$?
case $rc in
 0) exit 0;;
esac

# ps options for Linux:
# -o field1= -o field2= ... -- output these fields, with no header line
# -p -- (needs to be last) show process with pid ...
psopts='-o ppid= -o pid= -o args= -p'

# terminating condition: stop looping when comm= matches one of these
toplvl='-bash | SCREEN | init'

p=$$
echo "traceback for process $p:" >&2

while true; do
    set -- `ps $psopts $p`
    p=$1
    shift
    ######## FIXME: horrid
    cwd=$(set -- $(lsof -d cwd -a -p $1 | tail -n 1); echo "$9")
    echo '*' "$@" "(cwd: $cwd)" >&2
    #lsof -p $1 | sed 's/^/** /'
    case $1 in 0|1) break;; esac
    eval case \$2 in $toplvl\) break\;\; esac
done

exit $rc