How to make file lock with bash

问题

I have a task to rsync a dir from remote server

rsync -av root@s0.foo.com:/srv/data/ /srv/data/ 

To make it run regularly and avoid Script "reEnter" issue, I create a file lock "in_progress" with rsync progress's pid, which indicate whether the program is still running.

lock(){
    echo $1 > in_progress
}

Using this function to judge whether the rsync progress is still running:

is_running(){
   pid=$(cat in_progress)
   return ps aux | awk '{print $2}' | grep $pid
}

I can get the pid to pass to function lock with this

$!

I had to put the rsync progress background to get the pid of rsync, so I get this

rsync -av root@s0.foo.com:/srv/data/ /srv/data/ & 
lock $!

but when rsync progress is done, I should rm the lock file
I tried this

rsync -av root@s0.foo.com:/srv/data/ /srv/data/ && rmLock & 
lock $!

... then it seems the pid I got is not the pid of rsync progress :-(

回答1:

If you want to prevent simultaneous executions , flock is a nice tool:

$ flock -n /path/to/lock/file -c "rsync -av root@s0.foo.com:/srv/data/ /srv/data/" &

回答2:

( rsync -av root@s0.foo.com:/srv/data/ /srv/data/ && rmLock ) & 

Also

[ -d /proc/$pid ] && …

回答3:

I just find a way to solve this, using wait

rsync -av root@s0.foo.com:/srv/data/ /srv/data/ &
pid=$!
lock $pid
wait $pid
rmLock $pid

thanks to tijagi, I found a more elegant way to judge whether a progress is running.

来源：https://stackoverflow.com/questions/25863930/how-to-make-file-lock-with-bash