use strict;
my $str = 'FLAGSHARE
xxxxxx
xxxxx, 1 2015
words....
FLAGSHARE
xxxxxx
xxxxx, 2 2015
words....
FLAGSHARE
xxxxxx
xxxxx, 3 2015
words....';
my $regex = qr/FLAGSHARE[\S\s]*?\d\s*\d\n/p;
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