#!/usr/bin/perl -w

# services_sorter.pl
# sort /etc/services by numeric order of ports.
# Run this script as an unprivileged user.
# Use root or sudo to actually make changes:
# Rememeber to backup the original /etc/services file
# and to preserve permissions and ownership of the original 
# on the new /etc/services file.

use strict;

my $input = "/etc/services";

my $output = "services_out";

open (INPUT, $input) || die "Unable to open $input. " . $! .  "\n";
open (OUTPUT, ">>$output") || die "Unable to open $output. " . $! .  "\n";

my %service;
my @duplicates;

while (<INPUT>) {
    chomp (my $line = $_);
    next if ($line =~ /^\s*#/);
    next if ($line =~ /^\s*$/);
    $line =~ /^([^\s]+)\s+([^\s]+)/;
    my $label = $1;
    my $port = $2;
    my $comment;
    $line =~ s/^([^\s]+)\s+([^\s]+)\s+//;
    if ($line =~ /\w/) {
        $comment = $line;
        if ($comment !~ /^#/ ) {
            $comment = '# ' . $line;
        } elsif ($comment =~ /^#\w/) {
            $comment =~ s/^#/# /;
        }
    } else {
        $comment = '# ' . $label;
    }
    # add leading zeros to $key for string sort;
    my $key = $port;
    # we could very easily just use port like this  21/tcp, 21/udp
    # but due to sctp, we need to make an adjustment for numeric sorting
    $key =~ s/sctp/sct/ if ($key =~ /sctp/);
    my $str_len = length $key;
    while ($str_len < 17) {
        $key = "0" . $key;
        $str_len++;
    }
    # catch duplicates before we overwrite them
    if (defined $service{$key}{"port"} ) {
        push (@duplicates, $port);
    }
    $service{$key}{"label"} = $label;
    $service{$key}{"port"} = $port;
    $service{$key}{"comment"} = $comment;
}

close INPUT;

foreach my $key (sort keys %service) {
    my $label = $service{$key}{"label"};
    my $port = $service{$key}{"port"};
    my $comment = $service{$key}{"comment"};
    printf OUTPUT ("%-18s%18s%5s%-18s\n", $label, $port, " ", $comment);
}

foreach my $dup (@duplicates) {
    print "Duplicate found:  $dup\n";
}
print "If any duplicates were found, grep for them on the original file\n";
print "\nOutput is in $outfile.\nDone!\n";

close OUTPUT;
exit (0);