use strict;
use warnings;

my $cmdout = join '', <DATA>;
while ($cmdout =~ /^(.*?lines.*?)$/mg) {
    print "$1\n";
}

my @cmdout = split /\n/, $cmdout;
for (@cmdout) {
    print "$_\n" if m/lines/;
}

__DATA__
my multiple
lines of data
go here
and here are
some more lines
of data