防止shell脚本被重复执行

#!/bin/bash
LOCK_NAME="/tmp/my.lock"
if ( set -o noclobber; echo "$$" > "$LOCK_NAME") 2> /dev/null; 
then
trap 'rm -f "$LOCK_NAME"; exit $?' INT TERM EXIT

### 开始正常流程

sh /app/system.sh
sleep 30
### 正常流程结束

### Removing lock
rm -f $LOCK_NAME
trap - INT TERM EXIT
else
echo "Failed to acquire lockfile: $LOCK_NAME." 
echo "Held by $(cat $LOCK_NAME)"
exit 1
fi
echo "Done."