Why does this lisp function to grab text from buffer not work as I expect

Why does this lisp function to grab text from buffer not work as I expect

[acomber]

I have some text like this:

qwerty\tberty
merty\tserty

I want to grab the text berty between the tab character and end of line. 
Then to show it worked goto the end of the buffer and insert the text there.

But this code doesn't work.  Any ideas why not?






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Re: Why does this lisp function to grab text from buffer not work as I expect

[Barry Margolin]

In article <mailman.24033.1365776319.855.help-gnu-emacs@gnu.org>,
 acomber <deedexy@gmail.com> wrote:

> I have some text like this:
> 
> qwerty\tberty
> merty\tserty
> 
> I want to grab the text berty between the tab character and end of line. 
> Then to show it worked goto the end of the buffer and insert the text there.
> 
> But this code doesn't work.  Any ideas why not?
> 
> 
> 
> 
> 
> 
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> View this message in context: 
> http://emacs.1067599.n5.nabble.com/Why-does-this-lisp-function-to-grab-text-fr
> om-buffer-not-work-as-I-expect-tp283560.html
> Sent from the Emacs - Help mailing list archive at Nabble.com.

Invisible code tends to work poorly.

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

Re: Why does this lisp function to grab text from buffer not work as I expect

[Stephen Berman]

On Fri, 12 Apr 2013 07:18:26 -0700 (PDT) acomber <deedexy@gmail.com> wrote:

> I have some text like this:
>
> qwerty\tberty
> merty\tserty
>
> I want to grab the text berty between the tab character and end of line. 
> Then to show it worked goto the end of the buffer and insert the text there.
>
> But this code doesn't work.  Any ideas why not?
>
> (defun do-test ()
>   "tester"
>   (interactive)
>   (goto-char (point-min))
>   (if (search-forward "Option Name" nil t)
>      (delete-char 1) ;;delete tab
>      (setq myStr (buffer-substring point end-of-line)) ;add text to variable
>      ;goto end of buffer and insert text as demonstration it works
>      (goto-char (point-max))
>      (insert(myStr))
>   )
> )

point and end-of-line are functions, not variables, so they need to be
surrounded by parens.  But end-of-line moves point to the end of the
line and returns nil; that's also why you got the error you noted in
your other posting.  You should instead use the function
line-end-position: (buffer-substring (point) (line-end-position)).

Steve Berman

Re: Why does this lisp function to grab text from buffer not work as I expect

[Pascal J. Bourguignon]

Stephen Berman <stephen.berman@gmx.net> writes:

> On Fri, 12 Apr 2013 07:18:26 -0700 (PDT) acomber <deedexy@gmail.com> wrote:
>
>> I have some text like this:
>>
>> qwerty\tberty
>> merty\tserty
>>
>> I want to grab the text berty between the tab character and end of line. 
>> Then to show it worked goto the end of the buffer and insert the text there.
>>
>> But this code doesn't work.  Any ideas why not?
>>
>> (defun do-test ()
>>   "tester"
>>   (interactive)
>>   (goto-char (point-min))
>>   (if (search-forward "Option Name" nil t)
>>      (delete-char 1) ;;delete tab
>>      (setq myStr (buffer-substring point end-of-line)) ;add text to variable
>>      ;goto end of buffer and insert text as demonstration it works
>>      (goto-char (point-max))
>>      (insert(myStr))
>>   )
>> )
>
> point and end-of-line are functions, not variables, so they need to be
> surrounded by parens.  But end-of-line moves point to the end of the
> line and returns nil; that's also why you got the error you noted in
> your other posting.  You should instead use the function
> line-end-position: (buffer-substring (point) (line-end-position)).

And on the other hand, myStr is a variable, so why is it called as a
function in (insert (myStr)) ???

The OP seems to be totally confused between variables and functions…


Also, I don't see the relationship between "Option Name" and the example
text and problem statement…

Let's take it again from the start:

>> I have some text like this:
>>
>> qwerty\tberty
>> merty\tserty
>>
>> I want to grab the text berty between the tab character and end of line. 
>> Then to show it worked goto the end of the buffer and insert the text there.

(defun my-command ()
  (interactive)
  (goto-char (point-min)) ; not in the problem statement, but assumed.
  ;; I want to grab the text berty between tab and end-of-line:
  (when (re-search-forward "\t\\(berty\\)$" nil t)
    ;; We don't know what "it" is, in "show it worked", but
    ;; let's assume that "grab" implies deleting that text.
    (delete-region (match-beginning 1) (match-end 1))
    ;; Then to show it worked goto the end of the buffer
    (goto-char (point-max))
    ;;  and insert the text there.
    (insert "berty")))


So let's start with this buffer:
------------------------------------------------------------------------
qwerty	berty
merty	serty
------------------------------------------------------------------------
and type M-x my-command RET
we should get this buffer:
------------------------------------------------------------------------
qwerty	
merty	serty
berty
------------------------------------------------------------------------


-- 
__Pascal Bourguignon__                     http://www.informatimago.com/
A bad day in () is better than a good day in {}.