Shell Process Patterns

Start, supervise, and terminate shell processes safely -- background jobs, subshells, signal handlers, and cleanup. The dominant failure mode in this domain is silent state: a process that looks killed but still holds a port, a trap that looked fine but never fired on the child, a set -e script that kept running because || true swallowed the error. This skill picks the right pattern, implements it with the real PID (not the wrapper), and verifies the observable state afterward.

Pattern	Use When	Key Safety Bound
Background start	Ad-hoc long-running child in a script or session	Redirect fd 0/1/2, capture real PID, disown if parent exits
Daemonization	Process must survive terminal close, become session leader	`setsid` + fd redirect + write PID file atomically
PID resolution	Need to kill / inspect the actual worker	Re-query with `ss`/`pgrep`/`lsof`; `$!` is advisory, not authoritative
Signal discipline	Graceful shutdown of a supervisor + children	SIGTERM first with timeout, SIGKILL as last resort, propagate to process group
Trap + cleanup	Script must leave no orphans, lock files, or temp dirs	`trap ... EXIT` + verification (file gone, port free, PID dead)
Strict-mode scripts	Any non-trivial bash script	`set -euo pipefail` with understood `

shell-process-patterns

Shell Process Patterns

Scope