Re: do until sysopen()

tmpnam is not a builtin perl function, but is available with use POSIX qw(tmpnam);. You seem to use more control struct than is needed, as if you expect the system to need to retry a few times before giving you a file. It would be best to simply call tmpnam() once in sysopen(FH, POSIX::tmpnam(), O_RDWR|O_CREAT|O_EXCL) or die $!;

You might like to try IO::File:

use IO::File;
my $fh = IO::File->new_tmpfile();
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and you never need to know its name.

Update: Added import list for POSIX.

Update2: Scratched blunder, here is something that gets by tye's astute objection to your idiom:

use POSIX;
my ($tmpfh, $name);
do {
    $name = POSIX::tmpnam()
} until
    sysopen( $tmpfh, $name, O_RDWR|O_CREAT|O_EXCL)
    or                       # if error, then
        $! !~ m/File exists/ # try again if bad name
        &&  die $!;          # else die
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This depends strongly on lazy evaluation of logical operators.

After Compline,
Zaxo

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(tye)Re: do until sysopen() by tye (Sage) on Oct 22, 2001 at 19:58 UTC
It would be best to simply call tmpnam() once No, the point is that tmpnam() can give you the name of a file that doesn't exist and then, by the time you get a chance to call sysopen, someone else has created a file with that name. This is called a race condition. Specifying O_EXCL to sysopen means that it will fail if the race condition happens so that you can retry, which means requesting a new file name. But I wouldn't use the original code because, for one thing, it will just loop forever if sysopen is failing for a reason other than "file already exists". So I'd go with File::Temp (which isn't included with Perl [update: prior to version 5.6.1], unfortunately). Despite there being lots of methods avaiable for creating temporary files in Perl, it appears that only File::Temp "gets things right" and gets rid of the race conditions in a portable manner. Though I haven't investigated this thoroughly so I'd be happy to be proved wrong on that. (: - tye (but my friends call me "Tye")	[reply]

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(tye)Re: do until sysopen()
by tye (Sage) on Oct 22, 2001 at 19:58 UTC

It would be best to simply call tmpnam() once

No, the point is that tmpnam() can give you the name of a file that doesn't exist and then, by the time you get a chance to call sysopen, someone else has created a file with that name. This is called a race condition.

Specifying O_EXCL to sysopen means that it will fail if the race condition happens so that you can retry, which means requesting a new file name.

But I wouldn't use the original code because, for one thing, it will just loop forever if sysopen is failing for a reason other than "file already exists". So I'd go with File::Temp (which isn't included with Perl [update: prior to version 5.6.1], unfortunately). Despite there being lots of methods avaiable for creating temporary files in Perl, it appears that only File::Temp "gets things right" and gets rid of the race conditions in a portable manner. Though I haven't investigated this thoroughly so I'd be happy to be proved wrong on that. (:

tye

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