use strict;
my $str = '01090 C -------CALCULATION OF SOMETHING--
01100 "SOME.VARIABLE" = "SOME.OTHER.VARIABLE" + 2
01110 IF("SOME.VARIABLE" .NE. "SOME.VALUE") THEN ON("SOME.MACHINE")';
my $regex = qr/^\d{5}\t[cC] .*$(*SKIP)(*FAIL)|\h{2,}/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