Re: I can't believe: replace regexp in a string

[kai.grossjohann@uni-duisburg.de (Kai Großjohann)]

kamphausen@creativepharma.com (Stefan Kamphausen) writes:

> "Stefan Monnier <foo@acm.com>" <monnier+gnu.emacs.help/news/@flint.cs.yale.edu> wrote in message news:<5lheb6zwkj.fsf@rum.cs.yale.edu>...
>> 
>> I'm not sure what's your complaint exactly.
>> Is it that XEmacs' replace-in-string is not standard in Emacs (this
>> is addressed in Emacs-21 with replace-regexp-in-string) or is it
>> that you find both implementations of replace-in-string inefficient
>> (how is it implemented in Perl) ?
>
> I'm just wondering that such a trivial task (if your used to "$string
> =~ s/match-re/replace-re/" in Perl) like doing a match and replace on
> a string seems to be really non-trivial in Emacs, and I'm speaking of
> both Emacsen here. I thought I must have missed something somewhere.

Well, operations in a buffer are simpler, perhaps.

>> Finally, the reason why it took so long for Emacs to provide
>> replace-regexp-in-string is because Emacs uses buffers a lot more than
>> strings, so if you need replace-regexp-in-string it's maybe because you
>> made the arguably wrong decision to use a string rather than a buffer.
>
> Hm, I'm parsing a text file and need to replace some trailing
> whitespaces from a substring I just read. You're right in that I could
> do that replacement in the buffer I use for reading the files'
> contents (and thinking about that right now I might just do it that
> way ;-). Thanks for that hint.

Why does the substring contain the spaces in the first place?

Generally, when parsing a text file it is often better to use general
movement functions rather than to rely on regular expressions.
(Sometimes, regexes are the right tool even in Emacs.  But in Perl, a
regex is ALWAYS the right solution, in Emacs it SELDOM is.)

For example, you could frob the syntax correctly and then what you're
looking for might be a word, or a string, or an s-expression.

In your specific case, if you use searching in the buffer to find the
right spot, then you can use skip-syntax-backward or
skip-chars-backward to skip backwards over the trailing spaces.
Problem solved :-)

-- 
A turnip curses Elvis