problem re-search with the \| op.

problem re-search with the \| op.

[rtra]

Hi,

I'm having problems searching for a regular expression matching two
alternatives, A or B.
A = "#title "
B = "\* [A-Z][a-z]+.*"
and allow '.' (dot) to be string concatenation

(re-search-backward A 1 t) matches the string A as I intended, and
(re-search-backward B 1 t) also matches B as intended, but
(re-search-backward A."\|".B 1 t) does not matches A or B as I thought
it should

I'm using GNU Emacs 22.1.1, and testing this with a file like
----8<----
#title test
* tset

<point is here>
----8<----

Thank you for you time.
(I've wasted some in the manual, but I'm not figuring this out...)

Rui Almeida

Re: problem re-search with the \| op.

[Barry Margolin]

In article 
<ce71df65-e69f-415b-8d7a-721782e4445f@d70g2000hsb.googlegroups.com>,
 rtra <ruitra@gmail.com> wrote:

> Hi,
> 
> I'm having problems searching for a regular expression matching two
> alternatives, A or B.
> A = "#title "
> B = "\* [A-Z][a-z]+.*"
> and allow '.' (dot) to be string concatenation

'.' is string concatenation in Perl, not Lisp.  Lisp does everything 
using functions, not operators like this.  The string concatenation 
function is concat.

> 
> (re-search-backward A 1 t) matches the string A as I intended, and
> (re-search-backward B 1 t) also matches B as intended, but
> (re-search-backward A."\|".B 1 t) does not matches A or B as I thought
> it should

(re-search-backward (concat a "\\|" b) 1 t)

You need to escape the backslash because it has a special meaning in 
strings.

> 
> I'm using GNU Emacs 22.1.1, and testing this with a file like
> ----8<----
> #title test
> * tset
> 
> <point is here>
> ----8<----
> 
> Thank you for you time.
> (I've wasted some in the manual, but I'm not figuring this out...)
> 
> Rui Almeida

-- 
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
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