The "seek" function only works on disk files (no matter what programming language you're using), and cannot work on pipes.

If you need to make a routing decision after reading several lines from a pipe, you'll need to hold everything you read in a scalar or array until you are able to make your decision, and then send the accumulated stuff, along with whatever follows, to the appropriate recipient.

Update: So for example, something like: 

my @holdem;
my %dispatch = ( one => \&subone, two => \&subtwo );
my $target;

open( $pipe, "-|", "ls" );
while ( <$pipe> ) {
    if ( $target ) {
        $target->( $_ );
    }
    else {
        push @holdem, $_;
        my $decision = look_for_evidence( $_ );
        if ( $decision =~ /one|two/ ) {
            $target = $dispatch{$decision};
            $target->( $_ ) for ( @holdem );
        }
    }
}

[download]
(not tested)

In reply to Re: Can I seek in a command's piped output? by graff
in thread Can I seek in a command's piped output? by wardy3

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