You could do it using eval.

my $a = 10;
my $b = 20;
my $op = '>=';

if (eval "$a $op $b") {
  print "true\n";
} else {
  print "false\n";
}
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<http://www.dave.org.uk>

"The first rule of Perl club is you do not talk about Perl club."
-- Chip Salzenberg