From: mike@... (Mike Stok)
Date: 2004-02-01T06:55:02+09:00
Subject: Re: regex bug?

In article <20040131052700.GA5270@mulan.thereeds.org>,
Mark J. Reed <markjreed@mail.com> wrote:
>On Sat, Jan 31, 2004 at 01:07:42PM +0900, Zach Dennis wrote:
>> key = "file"
>> attrib = "\\Applications\\4Dapp\\Chess\\"
>> command = "xcopy [file] /y /s /e i:\\source\\"
>> command.gsub!( /\[#{key}\]/ , "#{attrib}" )
>> puts command
>> => "xcopy \\ApplicationsDapp\\Chess\\ /y /s /e i:\\source\\"
>
>As others have said, '\4' in a gsub string is special.  To get around
>this you need yet another backslash in front of it, which of course
>means two more backslashes between the double quotes:
>
>        attrib = "\\Applications\\\\4Dapp\\Chess\\"
>
>You can safely double all backslashes in gsub strings, so you might just
>want to make it special-processing-proof automatically with some
>preparatory munging of your own:
>
>        attrib = "\\Applications\\4Dapp\\Chess\\".gsub(/\\/, '\\\\\\')
>
>Just as a side note, if you're going to be making literal strings with
>backslashes, single quotes cut down on the number of doublings required:
>
>        attrib = '\Applications\4Dapp\Chess\\'.gsub(/\\/, '\\\\\\')

also if your replacement includes \ then you might consider using the
block form of gsub or gsub! to do the replacement as it doesn't parse
the replacement string for you (but does have some overhead):

[mike@ratdog mike]$ irb
>> key = "file"
=> "file"
>> attrib = "\\Applications\\4Dapp\\Chess\\"
=> "\\Applications\\4Dapp\\Chess\\"
>> command = "xcopy [file] /y /s /e i:\\source\\"
=> "xcopy [file] /y /s /e i:\\source\\"
>> command.gsub!(/\[#{key}\]/) { attrib }
=> "xcopy \\Applications\\4Dapp\\Chess\\ /y /s /e i:\\source\\"
>> puts command
xcopy \Applications\4Dapp\Chess\ /y /s /e i:\source\
=> nil

Hope this helps,

Mike

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