emacs regexp question

emacs regexp question

[gmayer]

Hello:

There are some regexps I don't know how to specify in gnu emacs:

- How should I ask for the first occurrence of two blank lines?

- How should I ask for the first occurrence of N blank lines for some fixed,
yet large, N. I think emacs uses ^ for the start of the line, though I've
seen some regexp libraries (not for emacs) that use the ^ as a sort of
"exponentiation" symbol for the number of times a string is concatenated.

- How can I search for regexps that have one or more newlines in the middle?

Brief explanations and/or brief examples of the above would greatly be
appreciated!

Thanks,

Mayer (gmayer@cs.bgu.ac.il)

Re: emacs regexp question

[D. Goel]

untested answers below, i hope they are not all wrong :-)


> Hello:
> 
> There are some regexps I don't know how to specify in gnu emacs:
> 
> - How should I ask for the first occurrence of two blank lines?

"\n\n" or C-q C-j C-q C-j if invoking M-x re-search-forward
interactively. -- that command is boundto C-M-s in some modes.


> 
> - How should I ask for the first occurrence of N blank lines for some fixed,
> yet large, N. 

"\n\n\n\n..."  I don't think there's another way to do it using emacs'
regexps.  perhaps regexp is not the right approach if N is very large,
and some simple elisp is in order.


> I think emacs uses ^ for the start of the line, though I've seen
> some regexp libraries (not for emacs) that use the ^ as a sort of
> "exponentiation" symbol for the number of times a string is
> concatenated.



> 
> - How can I search for regexps that have one or more newlines in the middle?

something like ".*\n.*"



DG                                 http://gnufans.net/
--

Re: emacs regexp question

[Jesper Harder]

D. Goel <deego@gnufans.org> writes:

>> - How should I ask for the first occurrence of N blank lines for
>> some fixed, yet large, N.
>
> "\n\n\n\n..."  I don't think there's another way to do it using emacs'
> regexps.

You can use the \{M\} postfix operator (M integer).

So e.g. "\n\\{500\\}" would match exactly 500 blank lines.

Re: emacs regexp question

[D. Goel]

> > "\n\n\n\n..."  I don't think there's another way to do it using emacs'
> > regexps.
> 
> You can use the \{M\} postfix operator (M integer).

Thanks Jesper.

Re: emacs regexp question

[Kevin Rodgers]

gmayer@cs.bgu.ac.il wrote:

> - How should I ask for the first occurrence of two blank lines?


interactively: ^ C-q C-j C-q C-j
programmatically: "^\n\n"


> - How should I ask for the first occurrence of N blank lines for some fixed,
> yet large, N. I think emacs uses ^ for the start of the line, though I've
> seen some regexp libraries (not for emacs) that use the ^ as a sort of
> "exponentiation" symbol for the number of times a string is concatenated.


interactively: ^ C-q C-j \{ N \}

programmatically: "^\n\\{N\\}"


> - How can I search for regexps that have one or more newlines in the middle?

interactively: \( .* C-q C-j \)*
programmatically: "\\(.*\n\\)*"

-- 
<a href="mailto:&lt;kevin.rodgers&#64;ihs.com&gt;">Kevin Rodgers</a>