Hi Brad,

within the do loop the $tempname variable is assigned a randomly chosen value between zero and $limit, which we can see is 99999. $md is then assigned the value of $TMPDIR (not listed in the code you provided) pluse the sring "/runitout_" and the value of $tempname. This will happen until no(the !) file exists (-f) for the value of $md shown in until (! -f "$md"); at the end of the do construct. It there are any parts you dont understand check out perldoc and the Tutorials section of this site. Perhaps the module File::Temp may also be of interest to you.

Comment version of your code:

my $limit = 99999;
my $md;

# Creates unique tmpfile
do {                                             #do the following 
    $tmpname = int(rand($limit));                #$tmpname = convert t
+o integer random number between 0 and $limit (99999)
    $md      = "$TMPDIR/runitout_$tmpname";        #$md = "$TMPDIR/run
+itout_$tmpname" concatinated values of $TMPDIR (not listed) the strin
+g "/runitout_" and the value of $tmpname
} until (! -f "$md");                             #until file $md does
+ not exist
[download]

Hope this helps.

Martin

Update: Fixed typo, later added a commented version of the user provided script