Perl Cookbook

Creating Temporary Files

Problem

You need to create a temporary file and have it automatically deleted when your program exits. For instance, you want to write a temporary configuration file to feed a program you launch. In this case, you want to know the temporary file’s name to tell the utility program. In other cases, you may just want a temporary file to write to and read from, and don’t need to know its filename.

Solution

If you don’t need to know the file’s name, use the new_tmpfile class method from the IO::File module to get a filehandle opened for reading and writing:

use IO::File;

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

If you need to know the file’s name, use the tmpnam function from the POSIX module to get a filename that you then open yourself:

use IO::File;
use POSIX qw(tmpnam);

# try new temporary filenames until we get one that didn't already exist
do { $name = tmpnam() }
    until $fh = IO::File->new($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 ...

Discussion

If you only need scratch space, the IO::File module’s new_tmpfile class method returns a filehandle connected to a temporary file that’s been opened read-write by using the following code:

for (;;) {
    $name = tmpnam();
    sysopen(TMP, $tmpnam, O_RDWR | O_CREAT | O_EXCL) && last;
}
unlink $tmpnam;

This file will ...