Shell Programming and Scripting

A quite safe mechanism for locking in a shell script is to create a locking directory. Call mkdir without the -p switch and if you succedd (exit code = 0) then your script can go on, or has to terminate otherwise.

But there still is the problem to remove the locking directory at program termination. If you are using ksh you can define a trap handler for the exit event like:

Code:

LOCKDIR=/tmp/mylock.dir
trap 'rm -rf $LOCKDIR' 0
if mkdir $LOCKDIR
then
    # go on
else
    print -u2 already running.
    exit 1
fi

Hi hergp!

Thank you for your help!
The script works, if i start the script while the script is running, there is the right message "script is running". But if i start it a second time, the mylock.dir directory is removed-> so i can start it though the script is already running. how can i prevent that the script removes the mylock.dir?

Do I have to copy my whole code instead of the "go on" comment?

Now, my code is under the if ... fi

Thank you

Greez Roger

Ah, I see. This issue can be corrected by undefining the trap in the else part of the if statement, like:

Code:

#!/bin/ksh
LOCKDIR=/tmp/mylock.dir
trap 'rm -rf $LOCKDIR' 0
if mkdir $LOCKDIR
then
    # go on
else
    print -u2 already running.
    trap : 0
    exit 1
fi

It's also possible, to move the first trap statement into the "go-on" part:

Code:

#!/bin/ksh
LOCKDIR=/tmp/mylock.dir
if mkdir $LOCKDIR
then
    trap 'rm -rf $LOCKDIR' 0
    # go on
else
    print -u2 already running.
    exit 1
fi

Hey hergp!

I have chosen the second solution. It seems to work correctly =D
Thank you for your help!

Who can mark this theard as resolved? or isnt it necessary?

Greez Roger