From: ts <decoux@...>
Date: 2002-10-01T20:36:50+09:00
Subject: Re: regex problem

>>>>> "P" == =?iso-8859-1?Q?Peter Sch=FCller?= <iso-8859-1> writes:

P> i want to substitute one \ with two \\

 It's in the faq, see

   http://www.rubycentral.com/faq/rubyfaq-9.html#ss9.18

Regexp.quote('\\') escapes a backslash. 

It gets trickier if you're using sub and gsub, Say you write gsub(/\\/,
'\\\\'), hoping to replace each backslash with two. The second argument is
converted to '\\' in syntax analysis. When the substitution occurs, the
regular expression engine converts this to '\', so the net effect is to
replace each single backslash with another single backslash. You need to
write gsub(/\\/, '\\\\\\')!

However, using the fact that \& contains the matched string, you could also
write gsub(/\\/, '\&\&').

If you use the block form of gsub, i.e. gsub(/\\/){'\\\\'}, the string for
substitution is analyzed only once (during the syntax pass) and the result
is what you intended.



Guy Decoux