use strict;
my $str = '25 * (233 - 1.5)
pow(25,2) / pi(); hack the pentagon;';
my $regex = qr~\b(?:p(?:i|ow)|m(?:in|ax))\b(*SKIP)(*FAIL)|[^0-9().,+*/\s-]+~mp;
my $subst = '';
my $result = $str =~ s~$regex~$subst~rg;
print "The result of the substitution is' $result\n";
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Perl, please visit: http://perldoc.perl.org/perlre.html