For expanding Anno's solution, you can use a dispatch table to apply the corresponding policy :
my %parsers = (
    'Ethernet' => sub {
        my $chunk = shift;
        $chunk =~ tr/\n/ /;
        return "ETHERNET: $chunk";
    },
    'Gigabit' => sub {
        my $chunk = shift;
        $chunk =~ tr/\n/ /;
        return "GIGABIT: $chunk";
    }
);

$/ = "!\n";
$\ = "\n";
while ( <DATA> ) {
    chomp;
    if ( /^interface (.*)/ && $1 && exists $parsers{$1} ) {
        print $parsers{$1}( $_ );
    } elsif ( /^system (.*)/ ) {
        # blah...
    }
}

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Edit: As anonymous said, ( ) instead of { }. Copypasta from/to Firefox is treacherous.

In reply to Re^2: Need advice on how to break foreach parsing loop into functions by Prof Vince
in thread Need advice on how to break foreach parsing loop into functions by ewhitt

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