Announcing perl1line.txt - A collection of handy Perl scripts | Hacker News Reader

Announcing perl1line.txt - A collection of handy Perl scripts

catonmat.net

74 pointspkrumins26 comments

It's missing one of my favorites:

    perl -MData::Dumper\ 999

Quickest way to get the version of a module you're running.

Doesn't work for File::Slurp, which has version 9999.19. :) Otherwise awesome thingy to query module versions.

Interesting. I would have done it this way previously:

  perl -MData::Dumper -e 'print $Data::Dumper::VERSION."\n"'

Works for any module:

    $ perl -MLWP::UserAgent\ 999             
    LWP::UserAgent version 999 required--this is only version 5.833.

  mike@server:~$ perl -MLWP::UserAgent -e 'print $LWP::UserAgent::VERSION."\n"'
  5.835
  mike@server:~$

That works, too!

Even shorter, as -l appends \n to all prints:

    $ perl -MLWP::UserAgent -le 'print $LWP::UserAgent::VERSION'

Even shorter!

    $ M=LWP::UserAgent && perl -M$M -le "print \$$M::VERSION"

Even even shorter!

    $ M=LWP::UserAgent;perl -M$M -Esay\$$M::VERSION

This reminds me of that joke in which jokes have been reduced to numbers. It's nearly as obscure, too.

Did Gödel come up with that joke?

Well, almost any module:

    $ perl -MFile::Slurp\ 9999
    <hangs forever>

I'm a fan of the "V" module.

   perl -MV=Data::Dumper

"Quicker", if you don't count install time.

   cpanm -n V

Shit like this is why Perl gets under my skin. The best way to do anything in Perl always seems to be some side effect of a clever hack, instead of actually solving the damn problem expressively.

The equivalent in Ruby?

    gem list $GEMNAME

It's shorter and more clear. Take that, Perl golfers!

Direct download link: http://www.catonmat.net/download/perl1line.txt

Making this for all the different languages would be awesome. I'm thinking PHP, jquery etc. one liners.

Do any other languages really lend themselves to the one line command tools like perl does?

The only one off the top of my head would be ruby but I don't have that much ruby knowledge to judge.

This kind of thing however is perl's bread and butter.

Benoit Hamelin did ruby one liners - http://benoithamelin.tumblr.com/ruby1line

Agreed - one reason why I still love Perl so much, despite its obvious warts.

Compared to Ruby, one liners are more efficient in Perl because the normally infuriating cryptic variables and defaults save space. For example in Perl you can run a foreach without naming the current iteration value and it defaults to $_. $_ in turn is the default target for many commands, like print.

So Perl's `print foreach @a` becomes Ruby's `a.each{|a| print a}`. Not so bad but it adds up.

Ruby:

   print a.join

Perl:

   print foreach @a

Ruby wins!

I think you mean:

    print @a;

Here's a page for Haskell: http://www.haskell.org/haskellwiki/Blow_your_mind

It isn't exactly the same--some examples are two or three lines and it's more about coolness than practicality--but it's in a similar spirit, and, more importantly, also interesting.

The first example:

-- split at whitespace -- "hello world" -> ["hello","world"] words

  unfoldr (\b -> fmap (const . (second $ drop 1) . break (==' ') $ b) . listToMaybe $ b)
 
  takeWhile (not . null) . evalState (repeatM $ modify (drop 1) >> State (break (== ' '))) . (' ' :)
    where repeatM = sequence . repeat
 
  fix (\f l -> if null l then [] else let (s,e) = break (==' ') l in s:f (drop 1 e))

Not really in the same spirit at all.

That blows my mind, but certainly not in a good way. Ruby:

    $ echo 'hello world' | ruby -e 'p STDIN.read.split'

Be aware that those are four separate examples made to showcase features of the language, the simplest of which being just `words`.

    split.hs:
    main = interact (show . words)

    $ echo hello world | runhaskell split.hs

OK, thats not really clear from the layout. Your example is clearer, but if you have to put it in a script and pipe stuff to it, its not really a 1-liner.

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