use strict;
use warnings;

my $tell = tell DATA;
while(<DATA>){
    if( /^(.*?):/ ) {
        my $client = $1;
        push @{$lines{$client}}, $tell;
        $triggered{$client}++ if /trigger/;
    }
    $tell = tell DATA;
}

print "Found triggers for ", join( ", ", keys %triggered ), ".\n";
for( keys %triggered ) {
    print "Log for client $_:\n";
    for( @{$lines{$_}} ) {
        seek DATA, $_, 0;
        my $line = <DATA>;
        print "\t$line";
    }
}

__DATA__
arthur: line 1
arthur: line 2 trigger
ford: line 3
# some comment
zaphod: line 4
zaphod: line 5 trigger
arthur: line 6
ford: line 7