The problem merlyn
is trying to point out is that when you open the file for writing (open (FH, ">file")
), you already deleted the contents of the file regardless of any locks. From perlopentut
To get an exclusive lock, typically used for writing, you have to be careful. We "sysopen" the file so it can be locked before it gets emptied. You can get a nonblocking version using "LOCK_EX | LOCK_NB".
use Fcntl qw(:DEFAULT :flock);
sysopen(FH, "filename", O_WRONLY | O_CREAT)
or die "can't open filename: $!";
or die "can't lock filename: $!";
or die "can't truncate filename: $!";
# now write to FH
Hope that helps!
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