Re: query-replace-regexp ... "Invalid repacement string '\.'"

[Malte Spiess]

David Kastrup <dak@gnu.org> writes:

> Malte Spiess <i1tnews@arcor.de> writes:
>
>> "s. keeling" <keeling@spots.ab.ca> writes:
>>
>>> Hi.  I was trying to make it easy on myself using q-r-r replacing
>>> '[^\]\.' (not a backslash, followed by a literal dot/period) with the
>>> string (sans quotes) '\.', essentially "escaping" every dot/period in
>>> the file.  "M-x query-replace" had no trouble with it but M-x
>>> query-replace-regexp refused, spouting the error message in the
>>> subject.
>>
>> In a regexp for a "\" you need to escape, so write "\\". "\]" is a
>> mistake.
>
> No, it isn't.  Inside of [], \ is not special.

Oh. Oops, sorry. Must admit I never used "\" inside of []. Didn't expect
a change there.

> Maybe something like
>
> M-x query-replace-regexp RET \(^\|[^\]\). RET \1\\. RET
>
> Or even
>
> M-x query-replace-regexp RET \(\(^\|[^\]\)\(\\\\\)*\). RET \1\\. RET
>
> (which considers a dot preceded by an even number of backslashes as
> unescaped).

In case he wants to replace the character before the "." as well (which
I doubt) '\\.' as a replacement string should do fine.

Else the proposed constructions with \(...\) and \1 (sometimes even \2
or \3) should work fine. This is a really useful feature, one should
learn how to use it to simplify lots of replacement tasks.

Greetings

Malte