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Atomic - Check file exists and create if not

dazzlad

Check file exists and create if not.

Can this be done as an atomic operation in Perl (cross platform).

Thanks.

Darren.

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Comments

Adam Stoller

Perhaps you're not providing enough detail - but are you talking about something like:if (! -e $fname){
if (open(OUT, '>', $fname)){
# put something in the file?
close(OUT);
}
else {
# error opening file for write
}
}
else {
# file already exists
}I'm not sure it's completely atomic, but it's pretty close and likely to be close enough without knowing more about the conditions you're worried about.

--fish
Senior Consultant, Quotient Inc.
http://www.quotient-inc.com

dazzlad

That snippet is exactly what I'm talking about.

I'm just being a perfectionist in looking for the atomic operation equivalent.

Thanks.

Darren.

stefanmaier

Hi Darren,
perhaps you can use

use POSIX;
my $fd = POSIX: Smiley Surprised

pen("test.html", O_CREAT|O_EXCL|O_WRONLY);
print "FileDescriptor=$fd\n";

If the file already exists, an undef is returned.
If there's no file, the file is created and you get back an file descriptor.

Open: don't know if POSIX: Smiley Surprised

pen itself is atomic. I assume it is not.

Stefan

birt_test.zip

dazzlad

Thanks for that!

Actually googling "POSIX:pen" +atomic seems to suggest that it is an atomic op!

Darren.