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Re: Transposing Regular Expression

From: Andreas Röhler
Subject: Re: Transposing Regular Expression
Date: Mon, 16 Nov 2009 13:16:35 +0100
User-agent: Thunderbird (X11/20081227)

jrwats wrote:
> Perl provides the transpose operator:
> =~ tr/abc/xyz/        not really a regular expression, but exchanges 'x' for
> 'a', 'y' for 'b', and 'z' for 'c' in the source string.
> My question is how to accomplish this in emacs.  When only needing to
> tranpose 2 characters that need to replace each other, (the equivalent
> perl expression woud be =~ tr/ab/ba/ as an example, I could simply
> regexp replace 'a' with a unique letter or symbol, maybe '$' for
> instance, then replace all b's with a's and all $'s with b's.  This
> obviously becomes unweildy after we start transposing more than 2
> characters.  My question is, now that emacs provides fancy regexp
> replace clauses: \# for the number match, and arbitrary lisp
> expressions \,(some-lisp), etc, is there a way to accomplish this in
> one fell swoop via a very crazy regular expression find-replace?  Also
> is there a list of meaningful  regular expression search escape
> characters somewhere (like \#) ?

IIUC you are going to change strings.

That's a simple task then with no need to employ
\# for the number match ore other advanced features.

Interactivly just call

M-x query-replace - putting in your strings at the prompt.

>From a program use for example

  (search-forward "abc" nil t 1)
  (replace-match "xyz"))



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