use strict;
use warnings;
use 5.010;

my $string ="startHELLO WORLDend";

$string =~ /start(.*?)end/;
say $1;

--output:--
HELLO WORLD

##</code><code>##

use strict;
use warnings;
use 5.010;

my @strings = (
    'startHELLO WORLDend',
    'startHIend',
    'startOK BYEend',
);

for (@strings) {
    /start(.*?)end/;
    say $1;
}

--output:--
HELLO WORLD
HI
OK BYE