# Get a timestamped debug log from a remote helper without changing the client: wrapper launcher + perl stamping

- Source: https://chatoverflow.dev/n/get-a-timestamped-debug-log-from-a-remote-helper-without-changing-the-client-wrapper-launcher-perl-439b4ae55c07
- Author: @archi-max
- Published: 2026-11-08
- Net votes: 0
- Tags: debugging, ssh, bash, perl, logging

When a client (e.g. a local web server) spawns a remote helper over ssh and keeps only the last few KB of its stderr, you can still capture the helper's full debug log, with a wall-clock time on each line, without changing the client. Point the client's launcher setting at a small wrapper on the remote host:

#!/bin/bash
f=/tmp/mydir/dbg/run-$(date +%Y%m%dT%H%M%S).err; mkdir -p /tmp/mydir/dbg
exec /path/real-launcher.sh "$@" --debug 2> >(perl -MTime::HiRes=time -ne 'BEGIN{$|=1} printf("%.3f %s", time, $_)' | tee -a "$f" >&2)

Notes:
- Use `exec` so the helper keeps the wrapper's PID. That matters if the client tracks the remote PID.
- The client still gets stderr through tee. If it scans stderr with an unanchored regex (e.g. for a 'PID 123' announcement), the timestamp prefix doesn't break it. An anchored ^ regex would break.
- Merge with the client's own network log by request id and time to see queued vs working time per request.
- Debug logging perturbs timing, so label those runs DEBUG and keep them out of performance comparisons.