Re: Mechaincal question Show filename of # marked

[Colin Walters <walters@cis.ohio-state.edu>]

Harry Putnam <reader@newsguy.com> writes:

> OK trying to get in to this, but I have no clue how that list might
> be stored into a variable... In the shell, no problem but in
> lisp.. I'm lost.

Ok.  By the way, I highly recommend Robert Chassell's "Programming in
Emacs Lisp: An Introduction".  It's how I started to learn Emacs Lisp.

> Taking the first example, since I don't know how to generate a
> variable containing a list I try using a single file name instead,
> and insert something simple for a shell command `cat' (UUofC not
> withstanding)

Well, one way to (implicitly) create variables is with `setq', which
you've probably seen before.

Say you type

(setq foo '("/home/reader/Mail/tmp/awk-work/13"
            "/home/reader/Mail/tmp/awk-work/14"))

This is sort of like saying

FOO="/home/reader/Mail/tmp/awk-work/13 /home/reader/Mail/tmp/awk-work/14"

in a shell, because you separate elements in a shell list with
whitespace.  In the same way that you could then say (in bash)

for x in $FOO; do cat $x; done

you can say

(dolist (x foo)
  (shell-command-to-string (concat "cat " x)))

Of course, Lisp lists are tons better, because they don't get confused
by whitespace, can store any kind of object, and get automatically
freed when you're done with them :)

> I'm guessing this is like a simple `for loop' and cat will be run on
> each member in turn.   So with just 1 member then maybe just on it.

Right.

> (mapcar (lambda (x) (shell-command-to-string (concat "cat " x)))
>         /home/reader/Mail/tmp/awk-work/13)
> 
> So C-x C-e
> Symbol's value as variable is void: \
> /home/reader/Mail/tmp/awk-work/13

Well, what you want to say here is:

(mapcar (lambda (x) (shell-command-to-string (concat "cat " x)))
         '("/home/reader/Mail/tmp/awk-work/13"))

So what you're doing here is creating a one-element list, with a
string as its single element.

> Well, I'm getting closer... May sound terribly lame, but I don't even
> have a clue on how to begin looking this up in the Into or Lisp
> manual.

The Elisp intro is very good, and worth reading.

> Good thing this isn't explosive... I'd have had a serious accident
> by now.

I still get that feeling pretty often :)