Keeping 2 people from updating a file at the same time.

[WaltS]

I am attempting to set a tempoorary 'lock' file so that another user cannot update a certain file while the lock file exists.
while [file exists $file.lck]{
wait 1
}
The problem I am having is when the lck file is removed, the program does not jump out of the while loop. We use something similar in our Korn Shell scripts which works fine.

 

[ulis]

Your code evaluates the ' [file exists $file.lck]' condition only once: before the lock file is removed.

The while command is evaluated by Tcl as all other commands: Tcl evaluates the var references '$var' and script calls '[script]' of the command line before calling the command.
So, because the lock file is here, your while command is like:

while 1 {wait 1}

To avoid that you need to protect the script call by braces to let the while command evaluate it.

Try:

while {[file exists $file.lck]} { wait 1 }

and all should be fine.

Good luck

ulis