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I am looking to sort a list of domain names (a web filter whitelist) starting from the TLD and working upwards. I am looking any *nix or windows tools that can do this easily, though a script would be fine too.

So if the is the list you are given

This is what I want as the output.

Just in case you are wondering why, Squidguard, has a bug/design flaw. If both and are both included in a list, then the entry is ignored and you can only visit content from I have several large lists that need some cleanup because someone added entries without looking first.

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Shouldn't the com domains appear before edu in your sorted list? – Sven Feb 28 '12 at 2:01
Yup, I fail at manual sorting, which is why I am looking for a tool. :) – Zoredache Feb 28 '12 at 2:04
Also, the python version there is nice compared to perl version because pythons's sort works on lists of lists; perl's sort doesn't and had to be implemented. – Mark Wagner Feb 28 '12 at 5:11

6 Answers 6

up vote 10 down vote accepted

This simple python script will do what you want. In this example I name the file

#!/usr/bin/env python
from fileinput import input
for y in sorted([x.strip().split('.')[::-1] for x in input()]): print '.'.join(y[::-1])

To run it use:

cat file.txt | ./

Note that this looks a little uglier since I wrote this as more or a less a simple one-liner I had to use slice notation of [::-1] where negative values work to make a copy of the same list in reverse order instead of using the more declarative reverse() which does it in-place in a way that breaks the composability.

And here's a slightly longer, but maybe more readable version that uses reversed() which returns an iterator, hence the need to also wrap it in list() to consume the iterator and produce a list:

#!/usr/bin/env python
from fileinput import input
for y in sorted([list(reversed(x.strip().split('.'))) for x in input()]): print '.'.join(list(reversed(y)))

On a file with 1,500 randomly sorted lines it takes ~0.02 seconds:

Elapsed (wall clock) time (h:mm:ss or m:ss): 0:00.02
Maximum resident set size (kbytes): 21632

On a file with 150,000 randomly sorted lines it takes a little over 3 seconds:

Elapsed (wall clock) time (h:mm:ss or m:ss): 0:03.20
Maximum resident set size (kbytes): 180128

Here is an arguably more readable version that does the reverse() and sort() in-place, but it runs in the same amount of time, and actually takes slightly more memory.

#!/usr/bin/env python
from fileinput import input

data = []
for x in input():
   d = x.strip().split('.')
for y in data:
   print '.'.join(y)

On a file with 1,500 randomly sorted lines it takes ~0.02 seconds:

Elapsed (wall clock) time (h:mm:ss or m:ss): 0:00.02
Maximum resident set size (kbytes): 22096

On a file with 150,000 randomly sorted lines it takes a little over 3 seconds:

Elapsed (wall clock) time (h:mm:ss or m:ss): 0:03.08
Maximum resident set size (kbytes): 219152
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I liked seeing lots of solutions. I am accepting the python based answer mostly because it is what I use for many of my other scripts. The other answers all seem to work also. – Zoredache Feb 28 '12 at 23:46

Here's a PowerShell script that should do what you want. Basically it throws all the TLD's into an array reverses each TLD, sorts it, reverses it back to its original order, and then saves it to another file.

$TLDs = Get-Content .\TLDsToSort-In.txt
$TLDStrings = @();

foreach ($TLD in $TLDs){
    $split = $TLD.split(".")
    $TLDStrings += ,$split

$TLDStrings = $TLDStrings|Sort-Object

foreach ($TLD in $TLDStrings){[array]::Reverse($TLD)}

$TLDStrings | %{[string]::join('.', $_)} | Out-File .\TLDsToSort-Out.txt

Ran it on 1,500 records - took 5 seconds on a reasonably powerful desktop.

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It should be fairly simple to convert this script into bash or another language I think. – Mark Henderson Feb 28 '12 at 2:44
5 seconds seems like a long time for only 1,500 lines. My python implementation does 1,500 in a fraction of a second, and 150,000 in just over 3 seconds. What do you suppose makes it so slow in PowerShell? – aculich Feb 28 '12 at 8:19
Yeah it is a long time. I've no idea why it takes so long though. Probably because powershell isn't really aimed at doing things like this. – Mark Henderson Feb 28 '12 at 9:46

Slightly less cryptic, or at least prettier, Perl:

use warnings;
use strict;

my @lines = <>;
chomp @lines;

@lines =
    map { join ".", reverse split /\./ }
    map { join ".", reverse split /\./ }

print "$_\n" for @lines;

This is a simple example of a Guttman–Rosler transform: we convert the lines into the appropriate sortable form (here, split the domain name on periods and reverse the order of the parts), sort them using the native lexicographic sort and then convert the lines back to their original form.

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Here it is in (short and cryptic) perl:

#!/usr/bin/perl -w
@d = <>; chomp @d;
for (@d) { $rd{$_} = [ reverse split /\./ ] }
for $d (sort { for $i (0..$#{$rd{$a}}) {
        $i > $#{$rd{$b}} and return 1;
        $rd{$a}[$i] cmp $rd{$b}[$i] or next;
        return $rd{$a}[$i] cmp $rd{$b}[$i];
} } @d) { print "$d\n" }
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Do you have timing information for this sort? I'm curious to see how this compares to @Mark-Henderson's PowerShell implementation, as well as my Python implementation. I used /usr/bin/time -v for the elapsed time and max memory stats. – aculich Feb 28 '12 at 8:21
Perl totally WINS at obfuscation. – Massimo Feb 28 '12 at 11:14
Describing a Perl script as "short and cryptic" is redundant. – Belmin Fernandez Feb 28 '12 at 12:31
@aculich, with the exception of the powershell script, all the options seem to take less then a 0.1 seconds on my file. – Zoredache Feb 28 '12 at 23:45

In Unix scripting: reverse, sort and reverse:

awk -F "." '{for(i=NF; i > 1; i--) printf "%s.", $i; print $1}' file |
  sort |
  awk -F "." '{for(i=NF; i > 1; i--) printf "%s.", $i; print $1}'
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cat domain.txt | rev | sort | rev

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I guess that would work. I do like having the TLD be sorted though, and this wouldn't accomplish that. Using this, the TLDs in my example would be in the order (uk, mil, pl, com, edu, gov) Since it is is a simple right to left sort, instead of the domain boundaries. – Zoredache Feb 4 at 22:48

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