SPUG: Does -i invocation lock files? was Re: Does tie()...

Lou Hevly lou at visca.com
Fri Jun 16 03:32:01 CDT 2000

At 09:49 14/06/00 -0700, Tim Maher/CONSULTIX wrote:
>I'm teaching my "Intermediate Perl" class this week, and some questions
>about file-locking have arisen.  I could probably find the answers myself by
>reading some source code, but I'd rather spend my time helping my students
>on their lab assignments instead, so I thought I'd ask if anybody knows
>the answers:
>	1) Does the -i invocation option lock the files it processes?
>	(Seems like it should, but if it does, that's not documented!)

AFAIK, whether or not the -i invocation locks is irrelevant if you use 'semaphor' file locking; you might point your students to Mark-Jason Dominus's article at

Here's a demo that deletes a username from .htpasswd; if this *isn't* foolproof, then I would very much appreciate hearing how it might fail. We'll assume that this is either the only program on the system writing to .htpasswd, or that all other programs that do use the same semaphor locking file.

use Fcntl qw(:flock);
@ARGV = '/path/to/.htpasswd';
my $semaphor = '/path/to/file.lock';
open S, "> $semaphor" or die $!;
flock S, LOCK_EX;
$^I = '.orig';
while (<>) {
  print unless /^$username/
close F;  close S;

All the best (Adéu-siau),
Lou Hevly
lou at visca.com

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