Interesting issues with split function

podian has asked for the wisdom of the Perl Monks concerning the following question:

Hello, I was trying to test how split works and ran into this issue. Please help:

#test 1
$s ="This   is   a   test";
$d =" ";

  print "--- output 1 --- \n";
    @ar = split($d, $s);
    foreach $i (@ar) {
    print "|$i| \n";
    }

   #test 2
   #how come this one prints differently?
   print "--- output 2 --- \n";
   @ar = split(" ", $s);
    foreach $i (@ar) {
    print "|$i| \n";
    }
[download]

First one prints this:

--- output 1 --- 
|this| 
|| 
|| 
|is| 
|| 
|| 
|a| 
|| 
|| 
|| 
|test|
[download]

I think this is the correct behavior. But the second one prints like this(when delimiter is used directly):

--- output 2 --- 
|this| 
|is| 
|a| 
|test|
[download]

I am using perl 5.8.5 on linux. Thanks a lot!
I am sorry I made a change to the question -- originally I had $delim = " " (instead of $d = " ") which was a typo.

Comment on Interesting issues with split function Select or Download Code

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Re: Interesting issues with split function by dragonchild (Archbishop) on Dec 03, 2004 at 17:31 UTC
" " is special-cased to be equivalent to /\s+/. It's mentioned in `perldoc -f split`, in case you're wondering. Being right, does not endow the right to be rude; politeness costs nothing. Being unknowing, is not the same as being stupid. Expressing a contrary opinion, whether to the individual or the group, is more often a sign of deeper thought than of cantankerous belligerence. Do not mistake your goals as the only goals; your opinion as the only opinion; your confidence as correctness. Saying you know better is not the same as explaining you know better.	[reply] [d/l]
Re: Interesting issues with split function by BrowserUk (Patriarch) on Dec 03, 2004 at 17:31 UTC
Because you defined `$delim = " "` but then used `@ar = split(`$d`, $s);`. use strict would have caught that typo for you. Examine what is said, not who speaks. "But you should never overestimate the ingenuity of the sceptics to come up with a counter-argument." -Myles Allen "Think for yourself!" - Abigail "Time is a poor substitute for thought"--theorbtwo "Efficiency is intelligent laziness." -David Dunham "Memory, processor, disk in that order on the hardware side. Algorithm, algorithm, algorithm on the code side." - tachyon	[reply] [d/l] [select]
Re^2: Interesting issues with split function by ysth (Canon) on Dec 03, 2004 at 18:12 UTC
Good catch. (The OP seems to have silently corrected this; see http://perlmonks.thepen.com/412187_orig.html.)	[reply]
Re: Interesting issues with split function by Joost (Canon) on Dec 03, 2004 at 17:38 UTC
From the docs: As a special case, specifying a PATTERN of space (' ') will split on white space just as "split" with no arguments does. Thus, "split(' ')" can be used to emulate awk's default behavior, whereas "split(/ /)" will give you as many null initial fields as there are leading spaces. A "split" on "/\s+/" is like a "split(' ')" except that any leading whitespace produces a null first field. A "split" with no arguments really does a "split(' ', $_)" internally. So $delim is always interpreted as a pattern, even if it contains only a single space, because it is not the " " literal. "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply]
Re: Interesting issues with split function by ikegami (Patriarch) on Dec 03, 2004 at 18:11 UTC
(It seems your question was edited. It would have been nice if you had left the original question there, and either posted a reply, or appended your update to your original post.) If I were to guess why it prints differently, I'd say the special case for split(" ") is handled at compile time and looks for a string literal. Use `$d = "\\s+";` or `$d = qr/\s+/;` instead of `$d = " ";`.	[reply] [d/l] [select]