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

why won't this work? 
#!/usr/bin/perl
use warnings;
use strict;


my $should_be = <<"END_SHOULD_BE";
input is:
,  , 1
,  ,  , 2
,  ,  ,  , 3
,  ,  ,  ,  , 4
,  ,  ,  ,  ,  , 5
,  ,  ,  ,  ,  ,  , 6
,  ,  ,  ,  ,  ,  ,  , 7
,  ,  ,  ,  ,  ,  ,  ,  , 8
,  ,  ,  ,  ,  ,  ,  ,  ,  , 9
,  ,  ,  ,  ,  ,  ,  ,  ,  ,  , 10

output should be:
,, 1
,,, 2
,,,, 3
,,,,, 4
,,,,,, 5
,,,,,,, 6
,,,,,,,, 7
,,,,,,,,, 8
,,,,,,,,,, 9
,,,,,,,,,,, 10

output is:
END_SHOULD_BE

print "$should_be";



while (<DATA>)
{
    s{, +,}{,,}g;

    print $_;
}




__DATA__
,  , 1
,  ,  , 2
,  ,  ,  , 3
,  ,  ,  ,  , 4
,  ,  ,  ,  ,  , 5
,  ,  ,  ,  ,  ,  , 6
,  ,  ,  ,  ,  ,  ,  , 7
,  ,  ,  ,  ,  ,  ,  ,  , 8
,  ,  ,  ,  ,  ,  ,  ,  ,  , 9
,  ,  ,  ,  ,  ,  ,  ,  ,  ,  , 10

[download]

Replies are listed 'Best First'.
Re: remove spaces only between commas
by ikegami (Patriarch) on Sep 21, 2007 at 17:15 UTC

    The first match includes the second comma, so the second match will start at the third one. 

    Before s///:     ,  ,  ,  ,  ,  ,  , 6
After 1st pass:  ,,|  ,  ,  ,  ,  , 6
After 2nd pass:  ,,  ,,|  ,  ,  , 6
After 3rd pass:  ,,  ,,  ,,|  , 6

    [download]

    The | indicates where a substition ended and from where the next pass will search.

    Solution 1: Start from the begining instead of where the last match left off. 

    1 while s{, +,}{,,};

    [download]

    Solution 2: Use a zero-width match to check for the "closing" comma. 

    s{, +(?=,)}{,}g;

    [download]
[reply]
[d/l]
[select]
      thanks ikegami. solution 2 is perfect.
[reply]

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