Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question: 

# get a temp file name 
do { $name = tmpnam() }
    until sysopen(FH, $name, O_RDWR|O_CREAT|O_EXCL);

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am I wrong in thinking that the above code is deprecated?

Replies are listed 'Best First'.
Re: do until sysopen()
by blakem (Monsignor) on Oct 22, 2001 at 11:22 UTC
    You can also use File::Temp, which can give you back an open filehandle and a filename. (thus avoiding various race conditions) 
    use File::Temp qw(tempfile);
my ($fh, $filename) = tempfile( DIR => $tmpdir );

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    -Blake

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[d/l]
Re: do until sysopen()
by Zaxo (Archbishop) on Oct 22, 2001 at 11:14 UTC

    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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      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")
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