Re: How to do search and replace with a lookup

[<tomas@tuxteam.de>]

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On Mon, Dec 11, 2017 at 12:49:47AM -0800, Angus Comber wrote:
> I have log file output like this:
> 
> Received device state message: pen state = 11 - uig state 10
> 
> where pen state and uig state are enums.
> 
> I want to do a search and replace where if for example pen state 11 enum is diagnostics and uig state 10 enum is starting, then I want the line to be updated to:
> 
> Received device state message: pen state = diagnostics - uig state starting
> 
> What is the easiest way to do this?
> 
> I can do search and replace using c-m-% and change for each permutation of number to string but that would be fairly labour intensive if enums were fairly long.  Can I combine that with a lookup somehow?  What is best way to do it?

If you do query-replace-regexp, you can use \,(...) in the
substitution text for a Lisp expression to be evaluated at
substitution time. You can pass it (parts of) the matched
string with the usual \0, \1, etc.

Thus if you have a mapping available for your enums which
is accessible from Lisp (an alist, a hash, whatever) you
should be half way there.

The manual[1] has a little example (it starts at the point
"Most readers can skip it", so make sure to *not* skip it :-)

The Emacs Wiki[2] has a couple of nice examples.

Just yell if you need more help.

Cheers
[1] https://www.gnu.org/software/emacs/manual/html_node/emacs/Regexp-Replace.html
[2] https://www.emacswiki.org/emacs/ReplaceRegexpWithLispExpressions

- -- tomás
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