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How do I make a temporary file name?

by faq_monk (Initiate)
on Oct 08, 1999 at 00:23 UTC ( #647=perlfaq nodetype: print w/ replies, xml ) Need Help??

Current Perl documentation can be found at perldoc.perl.org.

Here is our local, out-dated (pre-5.6) version:

Use the new_tmpfile class method from the IO::File module to get a filehandle opened for reading and writing. Use this if you don't need to know the file's name.

        use IO::File;
    $fh = IO::File->new_tmpfile()
            or die "Unable to make new temporary file: $!";

Or you can use the tmpnam function from the POSIX module to get a filename that you then open yourself. Use this if you do need to know the file's name.

    use Fcntl;
    use POSIX qw(tmpnam);

    # try new temporary filenames until we get one that didn't already
    # exist;  the check should be unnecessary, but you can't be too careful
    do { $name = tmpnam() }
        until sysopen(FH, $name, O_RDWR|O_CREAT|O_EXCL);

    # install atexit-style handler so that when we exit or die,
    # we automatically delete this temporary file
    END { unlink($name) or die "Couldn't unlink $name : $!" }

    # now go on to use the file ...

If you're committed to doing this by hand, use the process ID and/or the current time-value. If you need to have many temporary files in one process, use a counter:

    BEGIN {
        use Fcntl;
        my $temp_dir = -d '/tmp' ? '/tmp' : $ENV{TMP} || $ENV{TEMP};
        my $base_name = sprintf("%s/%d-%d-0000", $temp_dir, $$, time());
        sub temp_file {
            local *FH;
            my $count = 0;
            until (defined(fileno(FH)) || $count++ > 100) {
                $base_name =~ s/-(\d+)$/"-" . (1 + $1)/e;
                sysopen(FH, $base_name, O_WRONLY|O_EXCL|O_CREAT);
            }
            if (defined(fileno(FH))
                return (*FH, $base_name);
            } else {
                return ();
            }
        }
    }

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