Use CPAN://File::Temp.

Whether or not any directories on the system have old files removed periodically depends on the system's configuration, or if you haven't configured it, its defaults. So the first thing to do is poke around inside your system's documentation and/or cron configuration and see if it's already cleaning anything. If not, set it up to automatically clean /tmp, then write your files there.

File::Temp is a useful way to create tempfiles, but you'll still have to figure out how to get them cleaned up.

Also, it's best if you can clean them up yourself, and only leave them lying around in the rare case that your program crashes. Things like END blocks are useful places for this sort of cleanup.

Sick Unix Trick #347 ... ghost files.

# Open the file, creating it
open $fh, '+>', 'foo.txt';

# Immediately unlink the file ... it will remain
# until you close the filehandle, then disappear
unlink 'foo.txt';

# Put something in it to test
print $fh "Foo\n";

# Rewind to the start of the temp file
seek $fh, 0, 0;

# Read it back in and see what you have
$in = <$fh>;
print "Read: $in\n";

# You don't even *have* to remember to close it,
# but it is a good habit ...
close $fh;

By unix rules, the system normally should not remove anything from /tmp while running. In /tmp any program is supposed to be able to create files, write to them, and assume that files placed there will remain until removed by the owner. A program can not assume that the contents of /tmp will survive a reboot. That makes startup scripts the place for the system to do /tmp cleanup.

Some admins put in place some other policy they dream up, but the unix police will someday get 'em.

Putting /tmp on its own spindle, or at least a large partition, and mounting with the sticky bit set fixes most problems that non-unix policies are meant to solve. Going all BOFH on programs which don't clean up after themselves takes care of the rest.

Of course, users may clean up their own messes any time they like.

In re where to ask Unix/Linux qns, try www.linuxquestions.org, I think you'll like it.
Of course there are plenty of Unix/Linux monks here...