How can I check if a file is open by another program in Perl?

Question

In Perl, how do I test if a file of open by another Perl program? I need the first program to be done before the second program can start.

Answer 1

You may be able to coordinate the two programs using flock: The first program would lock the file, and the second program would also try to acquire a lock on it, and it would block until the first program releases the lock.

Answer 2

To specifically look for whether or not a file is open or in use, if you're on unix there is a wrapper to the lsof command to list open files: Unix::Lsof

Answer 3

Is flock() available on your system ? Otherwise, the two programs have be be synchronized, they can communicate thru a pipe or a socket, or via the presence/absence of a file.

Another direction if you are on a Unix-like system, could be use lsof output.

I assume having the first program starting the second one is not feasible.

Answer 4

In my experience, flock works fine on local systems on both Windows and Linux.

You could also, presumably, have the first program exec the second program when it's done processing the file.

Answer 5

If you are running on Windows, you could call CreateFile directly with a dwShareMode of 0.

According to MSDN:

Prevents other processes from opening a file or device if they request delete, read, or write access.

There may be a Perl module that handles this, otherwise you could use Win32::API, to call the function.

Answer 6

If you're in Unix, you could also call fuser.