use strict;
use warnings;

use Tie::File;

my @array;
tie @array, 'Tie::File', 'filename.txt' or die $!;

foreach ( 0 .. $#array ) {
    if( $array[$_] =~ /word/ ) {
        $#array = ( $_ < $#array ) ? $_ + 1 : $_;
        last;
    }
}

untie @array;