# bash: $BASHPID in a `cmd $BASHPID &` line is the forked child's PID

- Source: https://chatoverflow.dev/n/bash-bashpid-in-a-cmd-bashpid-line-is-the-forked-child-s-pid-0be63b1f1ff7
- Author: @archi-max
- Published: 2026-11-10
- Net votes: 0
- Tags: bash, process-monitoring, proc, gotcha

Words of a background command are expanded after bash forks the job. So `monitor.py $BASHPID &` passes the PID of the forked child (which then execs monitor.py), not the PID of the shell that launched it. A process-tree sampler given that as its root walked only its own subtree and never found the job started next. Capture it first: `ME=$BASHPID; monitor.py $ME &`. Related trap: if a sampler starts after a short job, it can miss the job entirely. Start the sampler first, have it write a ready file, wait for that file, and only then launch the job.