Nick Sieger

END {
  puts "Bye!"
}

puts "Processing..."

BEGIN {
  puts "One moment while I start your program"
}

One moment while I start your program
Processing...
Bye!

#!/usr/bin/env ruby -i

Header = DATA.read

ARGF.each_line do |e|
  puts Header if ARGF.pos - e.length == 0
  puts e
end

__END__
#--
# Copyright (C) 2007 Fancypants, Inc.
#++

#
# BEGIN

ARGF.each_line do |line| 
  if (line =~ /^# BEGIN/)..(line =~ /^# END/)
    puts line
  end
end

# END
# 

i = 5
while (i == 5)...(i == 10) do
  puts i
  i += 1
end

Constant =  "Constant"
@ivar = [1, 2, 3]
integer = 10

puts "const : #{defined?(Constant)}"
puts "ivar  : #{defined?(@ivar)}"
puts "global: #{defined?($0)}"
puts "local : #{defined?(integer)}"
puts "expr  : #{defined?(Constant + integer)}"

const : constant
ivar  : instance-variable
global: global-variable
local : local-variable
expr  : method

Tags ruby | 24 comments

Comments

Leave a response

1. nukeedit
   Jeremy McAnally said about 1 hour later:
   

   I think you misspelled your title:

   Obscene and Ugly Perlisms in Ruby

   There we go.

2. nukeedit
   Nathan said about 10 hours later:
   

   defined? comes in handy sometimes. I’ve even seen the output values used here and there. Since everything but false and nil evaluates to true, it might as well give extra information - and it can be very useful to be able to dynamically determine what’s defined as what.

3. nukeedit
   xan/hot@hot.com said about 10 hours later:
   

   You should provide the perl version of the ruby code too if you claim it is a Perlism.

   Also, the ‘;’ is not needed: integer = 10;

   Dont put more perl into ruby than in fact exists, I want to see the perl version of the code above too! ;-)

   Also $0 is $PROGRAM_NAME, lets use the longer names instead of the cryptic and hard-to-google perl legacy vars (they seem only useful for code golfing and one liners to me anyway)

4. nukeedit
   Nick said about 15 hours later:
   

   Nathan: Careful:

   defined?(false) => "false"
   defined?(nil)   => "nil"
   

   Maybe that’s not what you meant. As for its utility, I’ll wait until I see an example (although I’m not denying your claim that there is one). I couldn’t find any usage of defined? in the standard library that used the result for anything other than a boolean test.

   xan: Maybe the Perl code should be here, but the point is not to compare Ruby to Perl at the syntax level. Also, the examples are pretty simplistic (maybe too much so) and the equivalent Perl is not hard to imagine. But thanks for pointing out the semi! At least you can tell I was futzing with Perl a little bit during the preparation of the article.

   Everyone else: I don’t know why I initially said Perl is a “distant relative” -- I think I was getting overly dramatic with my prose. I’ve corrected that, as well as a side comment about quines -- someone seemed to think that was evidence I don’t know what they are. Whatever, it wasn’t adding anything, so it’s gone.

5. nukeedit
   Sixpack dude said about 15 hours later:
   

   Ex. A is an ‘awk-ism’ rather than a perl-ism. Read a book on Awk first, dude.

6. nukeedit
   Steve Stone said about 16 hours later:
   

   I actually find END blocks very useful in one-liners, particularly with the -n and -p switches.

   BEGIN blocks can have similar uses... though they’re really more useful for manipulating the interpreter at compile time. It’s important to understand the difference between “gets executed as the first thing in this code” versus “gets executed before any of the rest of this code is even compiled”.

7. nukeedit
   Robert Fischer said about 17 hours later:
   

   BEGIN blocks are extremely useful for generating methods at run-time or other cute stunts. I’ve never found a lot of use for END blocks, although I’ve heard some people use them to make sure all the filehandles are closed before a program exits.

   In either case, you use them because you either 1) you don’t have access to main thread of code being executed, or 2) you want to execute something before any other code even has a chance to be executed.

   It’s the kind of thing that seems worthless and silly until it is critical and necessary.

8. nukeedit
   Nathan said about 17 hours later:
   

   Nick:

   defined?(false) and defined?(nil) return strings, so something like

   if defined?(nil)
     puts "It's defined!"
   else
     puts "It's not."
   end

   works as you’d expect.

   One of the places I’ve used it is when writing plugins for Rails that can also operate outside of Rails. In this case I might do

   if defined?(ActiveRecord)
     class ActiveRecord::Base
       # Add relevant functionality
     end
   end

9. nukeedit
   Koz said about 20 hours later:
   

   Yeah, defined? is really useful when writing ‘really reflective’ code that gets used in places you don’t intend. For example the new routing optimisation code uses if defined?(request) to know if it can rely on using the request object to provide the host, protocol and port.

   However the particular string values returned don’t seem particularly useful. I thought it was a boolean until I used it in irb one day :).

10. nukeedit
    Ola Bini said 1 day later:
    

    Hi Nick,

    I kinda agree with some of what you write - defined? is totally more gross than it needs to be, but highly useful in some cases. For example, doing defined? on constants can be very nice. The string result is totally unnecessary, though.

    BEGIN can be useful in libraries sometimes, while END seems to not give anything more than at_exit.

    Flip-flops should DIEDIEDIE.

11. nukeedit
    Matthieu Riou said 1 day later:
    

    What about this?

    $irb

    foo = “foo” unless defined?(foo) foo => nil

    But:

    $irb

    unless defined?(foo) foo = “foo” end foo => “foo”

12. nukeedit
    riffraff said 1 day later:
    

    my 2c: I agree that the flip flop operator is rather obscure anod doesn’t deserve special syntax (it can be factored out into a class) but his behaviour is quite useful, and the equivalent ruby code without the flip flop hardly looks shorter and cleaner:

    tmp = false ARGF.each_line do |line| if tmp puts line tmp = !(line =~ /^# END/) else tmp = (line =~ /^# BEGIN/) end end

    Anyway while we’re at perlisms the example could also use $_ and regexps in conditionals :)

13. nukeedit
    Matthieu Riou said 1 day later:
    

    Mmmh the formatting didn’t quite work (guess I should have used pre blocks). The first snippet is with an unless as a single, the second inside a block. The => isn’t a hash, it’s the result produced by irb when you ask for the value of foo.

14. nukeedit
    Marsvin said 1 day later:
    

    I’m no expert, but I think BEGIN is used in Perl modules to do fancy stuff with the syntax tree and END is used to clean up things that the user of the module may not know about.

15. nukeedit
    Claus said 1 day later:
    

    <>, BEGIN/END and defined are natural and non-ugly in perl. It’s hard to convince a perl hacker that anything valuable is gained by throwing out the brevity of file I/O perl has. You’re missing the point of BEGIN/END - they are guaranteed to run, so they capture failure/exception conditions also, which makes them essential. Obviously defined is of less value in a pure OO language.

16. nukeedit
    Bruno Goncalves said 1 day later:
    

    The BEGIN and END clauses seem to have come straight out of awk where they actually make sense.

    http://www.bgoncalves.com/notes/2007/04/16/gawk-for-dummies-part-i/

    There they are executed before the first file is read and after the last file is read, respectively. Of course, in a more general purpose language they are mostly useless.

17. nukeedit
    Mark Thomas said 1 day later:
    

    I’ve used BEGIN and END in perl and found them very useful. In a persistent environment (PPerl, PerPerl, etc), the BEGIN clause is executed once only, whereas the body of the code is executed N times, with variables persisting between invocations. This lets you use BEGIN to establish connection pools, parse config files, and other one-time-only things. Likewise tear-down can go into END.

18. nukeedit
    Roger said 1 day later:
    

    Wow, a blogger ignorant of both basic Ruby and Perl! While it’s fine posing questions about a language’s syntax while you are learning it, claiming that what you don’t understand is ‘obscure’, ‘ugly’ and flawed is a red flag of a true poser.

19. nukeedit
    13az said 2 days later:
    

    Re: first comment....

      I think you misspelled your title:

      Obscure and Beautiful Perlisms in Ruby

    Has most peeps have already mentioned these aren’t all Perlisms (historically) and Perl does more things with these “Perlisms” than the context provided in your code.

    If Ruby is the bastard son of Perl then please treat it’s lineage with more respect ;-)

20. nukeedit
    Michael Bar-Sinai said 2 days later:
    

    Good post. Here’s my “favorite”. The ||= operator. Generally it means “populate a variable with a value unless the variable is already populated”.

    irb(main):029:0> a_var = 3 => 3 irb(main):030:0> a_var => 3 irb(main):031:0> a_var ||=”four” => 3 irb(main):032:0> a_var => 3

    So far so good, right?

    irb(main):033:0> a_var = false => false irb(main):034:0> a_var => false irb(main):035:0> a_var ||=true => true irb(main):036:0> a_var => true

    Now imagine you have a view that uses a (hopefully) boolean instance variable set in the controller (we’re talking rails here), and you want to set it to true if it is not already set. So you use ||=. So you spend the next 3 hours banging your head at the keyboard.

21. nukeedit
    andreas said 3 days later:
    

    @Michael Bar-Sinai

    irb(main):038:0> f_var = false
=> false

    irb(main):039:0> t_var = :somethingOtherValueExceptNilAndFalse
=> :somethingOtherValueExceptNilAndFalse

    irb(main):040:0> t_var
=> :somethingOtherValueExceptNilAndFalse

    irb(main):041:0> f_var ||= true
=> true

    irb(main):042:0> t_var ||= true
=> :somethingOtherValueExceptNilAndFalse
    
    So be careful with the BooleanGang!

22. nukeedit
    andreas said 3 days later:
    

    @Michael Bar-Sinai

    The ||= Operator in
    a ||= b
    stands for:
    a = a || b
    Meaning: Set a = a if a is not nil or false, otherwise set a = b (to the second argument of the exclusive logical or operator, short-circuit evaluation).
    The second argument b of the logical OR || operator will only be evaluated if the first argument a is false (or nil).

23. nukeedit
    bjc said 3 days later:
    

    Your accusation of the “flip-flor” is way off.

    “This program, when run with itself as an argument, prints out everything between BEGIN and END.”

    Which is exactly what the toggle code does.

    Your ruby code, on the other hand, prints out all the lines between 5 and 10, which in this example happens to be those lines between BEGIN and END.

    To call the programs equivalent would be a huge stretch of the word. And it also happens to show exactly why the “flip-flop” is useful.

24. nukeedit
    na said 3 days later:
    

    I’m a long-time Perl developer and have just recently switched to Ruby full-time.

    I love it. Great language. I’m surprised at how many Ruby developers are ignorant of much Perl has been incorporated. It’s a very simple switch from Perl to Ruby.

    I think there are a lot of great features of Ruby and hopefully it will get a bit faster (ahem).

    I never found Perl obscure and still don’t. I think most of that criticism comes from people versed in other more traditional languages who never really learned Perl well.