From: mike@... (Mike Stok)
Date: 2003-12-17T07:17:09+09:00
Subject: Re: substituting apostrphe's

In article <Pine.LNX.4.44.0312162108160.3096-100000@merlin.cs.kuleuven.ac.be>,
Peter  <Peter.Vanbroekhoven@cs.kuleuven.ac.be> wrote:
>> irb(main):003:0> a = "a"
>> => "a"
>> irb(main):004:0> a.gsub(/a/, '\'')
>> => "'"
>> irb(main):007:0> a = "abc"
>> => "abc"
>> irb(main):008:0> a.gsub(/a/, '\\\'')
>
>Did it again... The last line gives "bcbc" as result.
>

What do you want it to do?

You may be suffering from some horrid perl remnants, as $' is the
post-match variable, and in the perl debugger:

  DB<1> $s = 'abc'
 
  DB<2> $s =~ s/a/$'/g
 
  DB<3> print $s
bcbc

I postulate that because ri says this about String#gsub

------------------------------------------------------------ String#gsub
     str.gsub( pattern, replacement ) -> aString
     str.gsub( pattern ) {| match | block }  -> aString
------------------------------------------------------------------------
     Returns a copy of str with all occurrences of pattern replaced with
     either replacement or the value of the block. The pattern will
     typically be a Regexp; if it is a String then no regular expression
     metacharacters will be interpreted (that is /\d/ will match a
     digit, but '\d' will match a backslash followed by a 'd').
     If a string is used as the replacement, special variables from the
     match (such as $& and $1) cannot be substituted into it, as
     substitution into the string occurs before the pattern match
     starts. However, the sequences \1, \2, and so on may be used to
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
     interpolate successive groups in the match. These sequences are
     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
     shown in Table ?? on page ??.
     In the block form, the current match is passed in as a parameter,
     and variables such as $1, $2, $`, $&, and $' will be set
     appropriately. The value returned by the block will be substituted
     for the match on each call.
     The result inherits any tainting in the original string or any
     supplied replacement string.
        "hello".gsub(/[aeiou]/, '*')              #=> "h*ll*"
        "hello".gsub(/([aeiou])/, '<\1>')         #=> "h<e>ll<o>"
        "hello".gsub(/./) {|s| s[0].to_s + ' '}   #=> "104 101 108 108 111 "

Maybe you want to avoid the \ altogether

$ irb --simple-prompt
>> 'abc'.gsub(/a/, "'")
=> "'bc"
>> 'abc'.gsub(/a/) { "'" }
=> "'bc"

or you want to include a \ in the replacement

>> puts 'abc'.gsub(/a/, "\\\\'")
\'bc
nil
>> puts 'abc'.gsub(/a/) { "\\'" }
\'bc
=> nil

Hope this helps,

Mike
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