#!/usr/bin/perl

use v5.20;

my $s = <<'ENDSTR';
aaa       : AAA
bbb       : BBB
ccc       : CCC
ENDSTR

my $m = 'bbb';

my $a = $s =~ s/.*^$m *: (.*?)$.*/$1/rsm;
my $b = $s =~ s/[.\n]*?^$m *: (.*)$[.\n]*/$1/rm;

print "a: $a\n";
print "b: $b\n";