A question about debugging zsh using set -x to an independent log file

A question about debugging zsh using set -x to an independent log file

[Steven Lu]

[-- Attachment #1: Type: text/plain, Size: 885 bytes --]

I have a very highly instrumented zsh and am experiencing a particular
heisenbug. The zsh process just exits for no apparent reason. I have set
the OS to produce coredumps and this did not generate any when the issue
was reproduced.

I think that a reasonable approach to debugging that is very likely to
produce useful results is to use the set -x option to show each command
that ran. then at least I can see what area of plugins might be implicated.

The problem is that this is a heisenbug and it comes and goes, the shell
will be simply unusable when the xtrace output is there, and I can't really
use the shell effectively if I redirect stderr to a file. So I am hoping
there is a way to get the xtrace output and ONLY the xtrace output into a
separate file. If there is no feature in place I still expect that there
should be an easy way to patch zsh to allow me this.

Thanks.

Re: A question about debugging zsh using set -x to an independent log file

[Bart Schaefer]

On Apr 22,  7:56pm, Steven Lu wrote:
} 
} The problem is that this is a heisenbug and it comes and goes, the shell
} will be simply unusable when the xtrace output is there, and I can't really
} use the shell effectively if I redirect stderr to a file.

You probably want to use a trap on the DEBUG pseudo-signal, e.g.,

    TRAPDEBUG() {
      print -r -- "$ZSH_DEBUG_CMD" >> your_trace_file
    }

Or for closer congruence to set -x

    trap '{ print -nP -- "$PS4"
            print -r -- "$ZSH_DEBUG_CMD" } >> your_trace_file' DEBUG

This requires "setopt DEBUG_BEFORE_CMD" but unless you've deliberately
unset that, it is set by default.