#!/usr/bin/perl

# full script the following one liner:
# $ echo -e "abc\ndef\nghi\n" | perl -wlne '! /def/ and print "$_";'
# abc
# ghi

use strict;
use warnings;
use diagnostics;

my $B = "";
my $A = "abcdef
fhijkl
mnopqr
";

while ( $A =~ m{(.+)}g ) {
   $B .= "$1\n" unless $1 =~ /ijk/;
}
print "\$B = \n$B\n";


$B = "";
while ( $A =~ m{(.+)}g ) {
   $B .= "$1\n" while $1 =~ /ijk/;
}
print "\$B = \n$B\n";