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Posted by PerlFAQ Server on June 2, 2008, 9:03 am
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This is an excerpt from the latest version perlfaq5.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .
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5.22: I still don't get locking. I just want to increment the number in the
file. How can I do this?
Didn't anyone ever tell you web-page hit counters were useless? They
don't count number of hits, they're a waste of time, and they serve only
to stroke the writer's vanity. It's better to pick a random number;
they're more realistic.
Anyway, this is what you can do if you can't help yourself.
use Fcntl qw(:DEFAULT :flock);
sysopen(FH, "numfile", O_RDWR|O_CREAT) or die "can't open numfile:
$!";
flock(FH, LOCK_EX) or die "can't flock
numfile: $!";
$num = <FH> || 0;
seek(FH, 0, 0) or die "can't rewind
numfile: $!";
truncate(FH, 0) or die "can't
truncate numfile: $!";
(print FH $num+1, "\n") or die "can't write
numfile: $!";
close FH or die "can't close
numfile: $!";
Here's a much better web-page hit counter:
$hits = int( (time() - 850_000_000) / rand(1_000) );
If the count doesn't impress your friends, then the code might. :-)
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corrections to examples that do not work on particular platforms.
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