Q: How to copy a string in a text into a variable?

Q: How to copy a string in a text into a variable?

[gnuist]

Q: How to copy contents of kill ring into a string variable?

The purpose of these two questions above and the previous post is the 
same as below:

-------------------------------
My problem is very simple for an emacs guru. More than one solution is
very welcome.

I have a list of numbers in a file as follows:

ABC98789
DDE90898889
FRE9090909

that is, first three letters and then a string of numbers and nothing else.

I want to write a lisp function (not a macro) that can read the first
three letter substring into a variable and the rest of the substring into
another variable. Then I want to use these substrings to generate my
final string. I know that can be done using the "insert" command. The problem
is how to put the text strings in a file into a variable? I know setq can
do this but then if I construct the string in sexp such as:

(setq letters-variable "ABC")

how do I eval it? I have tried eval-last-sexp IN THE LISP FUNCTION
and it gives some strange result in the minibuffer when the function is run.

Any and all help is appreciated.

With a macro using C-k and yank this is trivial but the kill buffer can only
hold (memorize) one piece at a time not the two pieces. Still it can be done
by moving to the two lines where they are separately held, but it is not a 
readible solution. It is at the turing machine level of copy and erase one
at a time, not store in named variables.

Once I have written this function for one string, I can run it on the 
whole list by C-u 3 M-x my-function.

Cheers

Re: Q: How to copy a string in a text into a variable?

[Eric Marsden]

>>>>> "gd" == gnuist  <gnuist007@hotmail.com> writes:

  gd> Q: How to copy contents of kill ring into a string variable?

the kill ring is a list of strings: say C-h v kill-ring RET. 
The string that would be inserted by C-y is available as

   (car kill-ring-yank-pointer)
  
(though you shouldn't normally be manipulating the kill ring from an
elisp function; the kill ring is reserved for user interaction.)

  gd> I have a list of numbers in a file as follows:
  gd> 
  gd> ABC98789
  gd> DDE90898889
  gd> FRE9090909
  gd> 
  gd> that is, first three letters and then a string of numbers and nothing else.
  gd> 
  gd> I want to write a lisp function (not a macro) that can read the first
  gd> three letter substring into a variable and the rest of the substring into
  gd> another variable. Then I want to use these substrings to generate my
  gd> final string.

the buffer-substring function allows you to access the characters
between certain positions in a buffer. You probably want something
like the following:

(defun my-manipulation-function ()
  (interactive "*")
  (let (bol eol numbers letters)
    (save-excursion
      (save-match-data
        (beginning-of-line)
        (when (looking-at "[A-Z]\\{3\\}[0-9]+")
          (setq bol (point)
                eol (progn (end-of-line) (point))
                letters (buffer-substring bol (+ 3 bol))
                numbers (buffer-substring (+ 3 bol) eol))
          (beginning-of-line)
          (delete-region (point) eol)
          (insert numbers letters))))))

  gd> With a macro using C-k and yank this is trivial but the kill buffer can only
  gd> hold (memorize) one piece at a time not the two pieces.

actually, the kill ring contains a list of elements, so in theory it
could do this.

  gd> Once I have written this function for one string, I can run it on the 
  gd> whole list by C-u 3 M-x my-function.

if you can invoke it with M-x, it's a command rather than a function.

I suggest you read the Emacs Lisp Introduction; it's a good way to get
the feel of the language and how to program the Emacs.
  
-- 
Eric Marsden                          <URL:http://www.laas.fr/~emarsden/>

Re: Q: How to copy a string in a text into a variable?

[gnuist]

Eric Marsden <emarsden@laas.fr> wrote in message 
 
> the buffer-substring function allows you to access the characters
>     ^^^^^^^^^^^^^^^^
> between certain positions in a buffer

This was what I am looking for. But you have a number of pearls or
possibly bugs that I could not verify. Specifically, I am interested in a
dissection of the regular expression 

>         (when (looking-at "[A-Z]\\{3\\}[0-9]+")

and the conundrum is in \\{3\\}, a construct, which has no reference in 
the info page on emacs regular expressions.

You may as well explain the wisdom in the use of

    (save-excursion         ; ???
      (save-match-data      ; ???

which I fail to see despite seeing description on them.

Thanks a lot!!!!

Re: Q: How to copy a string in a text into a variable?

[Eric Marsden]

>>>>> "gd" == gnuist  <gnuist007@hotmail.com> writes:

  gd> But you have a number of pearls or possibly bugs that I could
  gd> not verify. Specifically, I am interested in a dissection of the
  gd> regular expression

  ecm> (when (looking-at "[A-Z]\\{3\\}[0-9]+")

  gd> and the conundrum is in \\{3\\}, a construct, which has no
  gd> reference in the info page on emacs regular expressions.

my Emacs manual has the following:
  
,----
| `\{N\}'
|      is a postfix operator that specifies repetition N times--that is,
|      the preceding regular expression must match exactly N times in a
|      row.  For example, `x\{4\}' matches the string `xxxx' and nothing
|      else.
`----

(You also have to know that in an elisp string, the '\' character is
an escape character, so you have to double it to get a literal '\'.)

  gd> You may as well explain the wisdom in the use of
  gd> 
  gd> (save-excursion         ; ???
  gd> (save-match-data      ; ???
  gd> 
  gd> which I fail to see despite seeing description on them.

the save-excursion is to avoid having command execution move point,
which is more polite. The save-match-data is due to me having used a
regexp function (looking-at), which sets the match data (some global
variables that allow functions like match-string to work); it's more
polite to save the match data to avoid changing it in the back of
another function.

(The save-match-data is probably not necessary, since this was inside
a command run from the keyboard, so it's unlikely to interfere with
other functions.)
  
-- 
Eric Marsden                          <URL:http://www.laas.fr/~emarsden/>