You need to compile the Perl code in $if, which is what eval EXPR does.

if (eval $if) {
    print "hi";
} else {
    print "hello";
}
[download]

But in the example you've shown, you're better off just storing a boolean value in $if:

$min = some number if defined
$max = some number if defined
$Files = some number 
$IdleTime = some number 

$if = 0;

$if = ($Files >= $max)
   if defined $max;

$if ||= ($IdleTime >= $min)
   if defined $min;

if ($if) {
    print "hi";
} else {
    print "hello";
}
[download]

Update: When using the eval method, you probably want to use single quotes when building up $if. Let eval do the interpolation.

The match logic can be made clearer and easier to debug like this:

  {
  next if ! defined ($max) and ! defined ($min);
  next if ! defined ($min) and $Files < $max;
  next if ! defined ($max) and $IdleTime < $min;
  next if $Files < $max and $IdleTime < $min;
  print "Match\n";
  last;
  }
  continue
  {
  print "No match\n";
  }
[download]

Use procedures. Here's a hypothetic example:

if (defined($max)) {
    $if = sub { ($Files >= $max) };
}
if (defined($min)) {
    if ($if) {
        my $oldif = $if; $if = sub { &$oldif() || ($IdleTime >= $min) 
+};
    } else {
        $if = sub { ($IdleTime >= $min) };
    }
}
# ...
# then you invoke it with
if (&$if()) {
    print "hi";
} else {
    print "hello";
}
[download]

And you may want to get a copy of MJD's HOP. I don't really know if it helps here, as I haven't yet got that book, but I think it may.

Update: don't belive what ikegami said above, eval-string is evil.

Update 2: but he's right about the boolean values, of course.

Hi,

If you'll use the $max and $min for presentation later you could initialize it with my $min = '';

So that you can still use it for comparisions because when converting into numeric will be 0 and at the same time you don't need to put "if defined" when you print it out, o use the ternary operator to print an alternative empty char, example:   if we're talking about a html output...

Regards,