Re: Transposing Regular Expression

[Andreas Politz <politza@fh-trier.de>]

jrwats <jrwats@gmail.com> writes:

> 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 \#) ?

You can use literal backreferences (e.g. \1) in the replacement part of
interactive uses of replace-regexp.  Combine that with expressions \,
and you could write a c-compiler in emacs-regexp/elisp.

The regular expression syntax is described in the elisp manual.

(info "(elisp)Regular Expressions")

-ap