(Pretty much what RonW said.) You require fast lookup over the $id field. Populate your data structure accordingly! Hash will be a good choice here.

If I understood correctly, the task is about grouping lines in a log file by the ID field, plus some additional munging. The following skeleton code might give you some ideas:

use strict;
use warnings;

# @ID to keep unique id's (in order they are seen)
# %T to group things by id. Make it HoA (Hash of Arrays)
my (@ID, %T);
...

while (<HANR>) {
    my ($date, $id, $kw) = /\[(.+?)\]/g;
    my $txt;

    next unless $kw;
    $txt = "$+ to P5"  if $kw =~ /^(Input Message)/;
    $txt = $+          if $kw =~ /^(Orchestration Started)$/;
    $txt = $+          if $kw =~ /^ProcessName:(.*)/;
    # note the opportunity to merge some regexes above
    next unless $txt;

    push @ID, $id unless $T{$id};
    push @{ $T{$id} }, "$date,$id,$txt \n";
}

for my $group (@T{ @ID }) {             # this is a hash slice!
    print OUT for @$group;
}
[download]

ps. I'm trying to puzzle out what hanr might stand for? And what is a displamer?

Update.

In above example, the @ID array is only to keep IDs ordered by their first encounter. If that's unimportant, replace the hash slice with just (values %T). The $+ is documented in perlvar. But my regex to split fields doesn't quite cut it if kw is not in brackets - needs a fix.

Having a firm handle on (perl) data structures is of great utility; it helps one in making the right algorithmic decisions. For starters, perldsc is a good read.

pps. I'm awfully suspecting that Hanr shot first. With a displamer.