use strict;
use warnings;
use Fcntl qw(:flock);
use Tie::File;

my $target_file = '.....';

{
    my ($tied, @file_content)

    $tied = tie @file_content, 'Tie::File', filename or die "Unable to tie $target_file: $!\n";
    $tied->flock(LOCK_EX|LOCK_NB) or die "Cannot lock $target_file. Aborting. $!\n";
    
    foreach my $line (@file_content) {
        $line =~ s/foo/bar/;
    }
}   # $tied falls out of scope. File is closed, lock expires.