[ruby-core:94420] [Ruby master Bug#16108] gsub gives wrong results with regex backreferencing and triple backslash

Issue #16108 has been updated by shyouhei (Shyouhei Urabe).

Status changed from Open to Rejected

This is a designed behaviour.  A backslash character is first cooked by the ruby interpreter (to handle `\'` etc), then cooked again by gsub's own preprocessor (to handle `\1` etc).  You have to understand exactly what is going on to play with it.

Don't hesitate to resort to the alternative solution shown in @alanwu's comment.

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Bug #16108: gsub gives wrong results with regex backreferencing and triple backslash
https://bugs.ruby-lang.org/issues/16108#change-80841

* Author: VivianUnger (Vivian Unger)
* Status: Rejected
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.6.3p62 (2019-04-16 revision 67580) [x64-mingw32]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN
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I have written a script to convert LaTeX indexing files (.idx) to Macrex backup format (.mbk), so that I can import LaTeX-embedded indexes into the Macrex indexing program. A problem arises when I try to convert bolded text. LaTeX indicates bolded text with the tag \textbf{} while Macrex wraps it in backslashes: \\.

In my test case, the input string is "\indexentry{\textbf{bold}|hyperpage}{2}", which I need to convert into "\indexentry{\bold\|hyperpage}{2}". For this I am using:

record.gsub(/\\textbf\{([^\}]+)\}/, '\\\1\\')

But instead of the expected output, I get:

\indexentry{\1\|hyperpage}{2}

...as if I only had \\ rather than \\\.

I have tried the same Regex in a search-and-replace in Notepad++ and it works as expected. It's only in Ruby that I get this unexpected result.

The kludgey workaround I have found is to leave a space before the \\:

record.gsub(/\\textbf\{([^\}]+)\}/, '\\ \1\\')

...giving the result:

\indexentry{\ bold\|hyperpage}{2}

But this won't do. Macrex complains and the extra space has to be edited out. Imagine if you have hundreds of lines with bold text in them!



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