use Modern::Perl;

open my $infh, '<', 'orders.txt';
open my $outfh, '>', 'orders.txt.tmp';

while( <$infh> ) {
    chomp;
    my @vals = split "\t";
    my $status = $vals[19];
    if( $vals[0] = 'trigger text' ) {
        $vals[19] = 'Delivered';
    }
    print $outfh join("\t",@vals), "\n";
}

close $infh;
close $outfh;
rename "orders.txt", "orders.txt.bak";
rename "orders.txt.tmp", "orders.txt";

##</code><code>##

use strict;
use warnings;
use Modern::Perl
use Tie::File;

tie my @lines, 'Tie::File', 'orders.txt' or die $!;
foreach my $line ( @lines ) {
    chomp $line;
    my @vals = split "\t", $line;
    if( $vals[0] == 'trigger text' ) {
        $vals[19] = 'Delivered';
    }
    $line = join( "\t", @vals ) . "\n";
}
untie @lines;