Write a daemon's PID to a file at start, check on subsequent runs, clean up on exit. Avoids two copies of the same daemon when the script is invoked twice.
Bash
#!/usr/bin/env bash
set -euo pipefail
PIDFILE="/var/run/myapp.pid"
# Already running?
if [[ -f "$PIDFILE" ]] && kill -0 "$(cat "$PIDFILE")" 2>/dev/null; then
echo "Already running as PID $(cat "$PIDFILE")" >&2
exit 1
fi
# Write our PID, clean up on exit
echo $$ > "$PIDFILE"
trap 'rm -f "$PIDFILE"' EXIT INT TERM
# ─── daemon body ─────────────────────────────────────
while true; do
echo "[$(date)] heartbeat"
sleep 60
doneSave your own code snippets
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