Stateful Parser in Perl

Here is a Perl implementation of the Python parser from my previous post. This is a direct port, so if you know one language and not the other then you can probably use these parsers to learn a little bit about the other language.

Some differences that I notice are that Python has a cleaner syntax. Also python favors string/list manipulation functions that return a new string as opposed to changing the string in place. That fact cleans up the code a lot, by allowing me to chain multiple functions together. A bonus for Perl is that it uses the same syntax for opening a file and opening a pipe to a subprocess.

Here is the code:

#! /usr/bin/env perl -w
use strict;

{
  package Parser;
  
  sub new {
    my ($class) = @_;
    my $self = {};
    $self->{state} = sub{$self->outside(@_)};
    $self->{interfaces} = [];
    bless $self, $class;
    return $self;
  }
  
  sub outside {
    my ($self, $line) = @_;
    if ($line =~ /^Network:/) {
      $self->{state} = sub{$self->network(@_)};
    }
  }
  
  sub network {
    my ($self, $line) = @_;
    if ($line =~ /^[^\s]/) {
      $self->{state} = sub{$self->outside(@_)};
    } else {
      if ($line =~ /^\s{4}\S/) {
        $line =~ s/^\s+//;
        $line =~ s/:\s+$//;
        push(@{$self->{interfaces}}, [$line]);
      } elsif ($line =~ /^\s*MAC Address:/) {
        $line =~ s/\s+$//;
        my $interface = pop(@{$self->{interfaces}});
        my @words = split(/: /, $line);
        push(@$interface, $words[1]);
        push(@{$self->{interfaces}}, $interface);
      }
    }
  }
}

package main;

sub main {
  my ($filename) = @_;
  if (! $filename) {
    $filename = "/usr/sbin/system_profiler |";
  }
  open(FILE, $filename) or die $!;
  my $parser = new Parser();
  while (<FILE>) {
    $parser->{state}($_);
  }
  foreach (@{$parser->{interfaces}}) {
    print join(" ", @$_) . "\n";
  }
}

main($ARGV[1]);

Here is the output:

py$ ./system_profiler.pl system_profiler.txt
Bluetooth
Ethernet 00:22:41:21:0b:77
FireWire 00:21:e9:ff:fe:ce:eb:1a
AirPort 00:21:e9:e1:10:0f
py$