kfiresmith · August 30, 2024 19:53 · Aug 30, 2024
diff --git a/demonstrate-pidfile-management.sh b/demonstrate-pidfile-management.sh
@@ -0,0 +1,39 @@
+#!/bin/bash
+
+
+# Obtain the name of the script dynamically so that we can re-use this code block on any script
+SCRIPT_FULLNAME="${0##*/}"
+# Trim off the file extension if one is present
+SCRIPT_TRIMMEDNAME="${SCRIPT_FULLNAME%.*}"
+
+# /run is superior to /tmp, but we can't write a lock file there if we aren't root.
+# We want to maintain the option of using this code block in scripts not run by root,
+#  so we fall back to using good old /tmp
+LOCK_DIR="/run"
+[ -w "$LOCK_DIR" ] || LOCK_DIR="/tmp"
+LOCK_FILE="$LOCK_DIR/$SCRIPT_TRIMMEDNAME.lock"
+
+# Function to remove the lock file on exit
+cleanup() {
+    rm -f "$LOCK_FILE"
+}
+# Trap to ensure PID file is removed even if the script is interrupted
+# This runs on exit whether the script was successful, failed, or interrupted.
+trap cleanup EXIT
+
+# Check if the PID file exists.  If it already exists, we just exit so that we don't
+#  create a cron pileup by re-running the running script again over itself.
+if [ -e "$LOCK_FILE" ]; then
+    echo "Script is already running. Exiting."
+    exit 1
+fi
+
+# If we've made it this far, write the current PID to the PID file. Now we can
+#  proceed with running the actual script
+echo $$ > "$LOCK_FILE"
+
+# Do stuff below
+
+
+# Remove the PID file (handled by the trap)
+exit 0