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^[$B5qH]!'^[(Bbadluck@arigatouo.net

re-search beginning of line or whitespace

[Tim Johnson]

Hi:
    I'd like to find the nearest previous whitespace *or*
beginning of line;
(re-search-backward "^")  ;; gets me to the beginning of
                          ;; the line
(re-search-backward "[\t ]") ;; seems to find the nearest
                             ;; previous whitespace
;; but can't seem to combine them properly
(re-search-backward "^\|[\t ]") ;; gives me an error

What am I leaving out.
TIA
tim

-- 
Tim Johnson <tim@johnsons-web.com>
      http://www.alaska-internet-solutions.com

Re: re-search beginning of line or whitespace

[Neon Absentius]

On Tue, Nov 01, 2005 at 05:39:46PM -0900, thus spake Tim Johnson:
> (re-search-backward "^\|[\t ]") ;; gives me an error
> 
> What am I leaving out.

A slash ;)

The correct syntax is (re-search-backward "^\\|[\t ]") with your
syntax you are searcing for a line starting with a pipe ("|") and
continuing with white space.  Appanently your buffer doesn't contain
such a line.

> TIA
> tim

-- 
Computer science is not about computers, any more than astronomy is
about telescopes.
        -- Edsger Dijkstra

Re: re-search beginning of line or whitespace

[Tim Johnson]

* Neon Absentius <absent@sdf.lonestar.org> [051101 18:30]:
> On Tue, Nov 01, 2005 at 05:39:46PM -0900, thus spake Tim Johnson:
> > (re-search-backward "^\|[\t ]") ;; gives me an error
> > 
> > What am I leaving out.
> 
> A slash ;)
 
  Thanks Neon:

> The correct syntax is (re-search-backward "^\\|[\t ]") with your
> syntax you are searcing for a line starting with a pipe ("|") and
> continuing with white space.  Appanently your buffer doesn't contain
> such a line.
  
  Let me see if I understand the logic of this strange creature called
  "regular expressions":

   "^"      ;; match beginning of line
   "\\|"    ;; seperator for alternatives
   "[\t ]"  ;; match any of: TAB, SPACE

   Am I correct? 
   I get confused by the way that emacs "escapes" metacharacters.

   Thanks again
   tim

-- 
Tim Johnson <tim@johnsons-web.com>
      http://www.alaska-internet-solutions.com

Re: re-search beginning of line or whitespace

[Neon Absentius]

On Wed, Nov 02, 2005 at 08:19:14AM -0900, thus spake Tim Johnson:
>   Let me see if I understand the logic of this strange creature called
>   "regular expressions":
> 
>    "^"      ;; match beginning of line
>    "\\|"    ;; seperator for alternatives
>    "[\t ]"  ;; match any of: TAB, SPACE
> 

It should really be two slashes: [\\t ].  That escaped me ;).

>    Am I correct? 
>    I get confused by the way that emacs "escapes" metacharacters.

It is explained nicely in the elisp manual:

,----[ (info "(elisp) Regexp Special") ]
| `\'
|      has two functions: it quotes the special characters (including
|      `\'), and it introduces additional special constructs.
| 
|      Because `\' quotes special characters, `\$' is a regular
|      expression that matches only `$', and `\[' is a regular expression
|      that matches only `[', and so on.
| 
|      Note that `\' also has special meaning in the read syntax of Lisp
|      strings (*note String Type::), and must be quoted with `\'.  For
|      example, the regular expression that matches the `\' character is
|      `\\'.  To write a Lisp string that contains the characters `\\',
|      Lisp syntax requires you to quote each `\' with another `\'.
|      Therefore, the read syntax for a regular expression matching `\'
|      is `"\\\\"'.
`----

You see, for the regular expression parser of emacs certain
characters have to be escaped for example "|" when one uses it to
indicate disjunction, so you write it "\|".  However when you write
a Lisp program the regexp is entered as a string, and since "\" is
an elisp escape character a sting that contains "\|" is interpreted
as "|".  You don't want that, you want the string to pass to the
"regexp machine" as is, you want the regexp to have "\|"; therefore
you have to escape the slash thus "\\|".  

I hope this makes some sense.

> 
>    Thanks again
>    tim
> 
> -- 
> Tim Johnson <tim@johnsons-web.com>
>       http://www.alaska-internet-solutions.com
> 
> 
> _______________________________________________
> Help-gnu-emacs mailing list
> Help-gnu-emacs@gnu.org
> http://lists.gnu.org/mailman/listinfo/help-gnu-emacs

-- 
Computer science is not about computers, any more than astronomy is
about telescopes.
        -- Edsger Dijkstra

Info [was Re: re-search beginning of line or whitespace]

[Tim Johnson]

* Neon Absentius <absent@sdf.lonestar.org> [051103 11:45]:
> On Wed, Nov 02, 2005 at 08:19:14AM -0900, thus spake Tim Johnson:
> It is explained nicely in the elisp manual:
> 
> ,----[ (info "(elisp) Regexp Special") ]
> | `\'
> |      has two functions: it quotes the special characters (including
> |      `\'), and it introduces additional special constructs.
> | 
> |      Because `\' quotes special characters, `\$' is a regular
> |      expression that matches only `$', and `\[' is a regular expression
> |      that matches only `[', and so on.
> | 
> |      Note that `\' also has special meaning in the read syntax of Lisp
> |      strings (*note String Type::), and must be quoted with `\'.  For
> |      example, the regular expression that matches the `\' character is
> |      `\\'.  To write a Lisp string that contains the characters `\\',
> |      Lisp syntax requires you to quote each `\' with another `\'.
> |      Therefore, the read syntax for a regular expression matching `\'
> |      is `"\\\\"'.
> `----
> 
> You see, for the regular expression parser of emacs certain
> characters have to be escaped for example "|" when one uses it to
> indicate disjunction, so you write it "\|".  However when you write
> a Lisp program the regexp is entered as a string, and since "\" is
> an elisp escape character a sting that contains "\|" is interpreted
> as "|".  You don't want that, you want the string to pass to the
> "regexp machine" as is, you want the regexp to have "\|"; therefore
> you have to escape the slash thus "\\|".  
> 
> I hope this makes some sense.
 
   Indeed. Thank you very much Neon.
   FYI: I use both Xemacs and GNU emacs. I note that from emacs and
        in invoking 'info' from the bash shell that I can not find
        a Menu item for emacs or elisp. It looks as if those
        components are not installed.

        In Xemacs, info provides "Lispref: (lispref)" as a menu
        item, which leads me to the regex topic.

  For GNU emacs, how may I install these missing items?

  cheers
  tim

-- 
Tim Johnson <tim@johnsons-web.com>
      http://www.alaska-internet-solutions.com

Re: re-search beginning of line or whitespace

[Johan Bockgård]

Neon Absentius <absent@sdf.lonestar.org> writes:

>>    "[\t ]"  ;; match any of: TAB, SPACE
>
> It should really be two slashes: [\\t ]. That escaped me ;).

No, it shouldn't. \\t is a backslash character followed by a t. \t is
the read syntax for a tab character.

-- 
Johan Bockgård

Re: re-search beginning of line or whitespace

[Neon Absentius]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset=iso-8859-7, Size: 512 bytes --]

On Fri, Nov 04, 2005 at 02:05:32AM +0100, thus spake Johan Bockg?rdÿ:
> Neon Absentius <absent@sdf.lonestar.org> writes:
> 
> >>    "[\t ]"  ;; match any of: TAB, SPACE
> >
> > It should really be two slashes: [\\t ]. That escaped me ;).
> 
> No, it shouldn't. \\t is a backslash character followed by a t. \t is
> the read syntax for a tab character.
> 

Yes indeed.

Oops!

-- 
Computer science is not about computers, any more than astronomy is
about telescopes.
        -- Edsger Dijkstra