[Proposal] Why not add a "shell" procedure?

[Nala Ginrut]

hi folks!
Sometimes we need to run shell script and get the result as string type.
Say, in Ruby:
irb: `ls`
==> 
"ice-9\nlanguage\nMakefile.am\nMakefile.am~\nMakefile.in\noop\nrnrs\nrnrs.scm\nscripts\nsrfi\nstatprof.scm\nsxml\nsystem\ntexinfo\ntexinfo.scm\nweb\n"

* Note: "system" lib function is useless for this, because "system"
can't return the result as string, but just the retval.

This feature is very easy to implement in Guile, but I recommend to
add a global env-var %current-shell to point any shell-interpreter,
like csh/bash/sh/..., or modify it as user wish.
The "shell" implementation maybe like this:
-------------code----------------
(define %current-shell (getenv "SHELL"))
(use-modules (ice-9 popen) (rnrs io ports))
(define shell
   (lambda (cmd)
       (let ((str (string-append %current-shell " -c " cmd)))
          (get-string-all (open-pipe str OPEN_READ)))))
-------------end----------------

and use it like regular shell:
(shell "sed -i \"s:guile/Guile/g" somefile")

Moreover, we can implement "pwd" with this "shell" easily:
----------code----------
(use-module (ice-9 rdelim))
(define (pwd)
  (call-with-input-string (shell "pwd")
                                     (lambda (port) (read-line port))))
-----------end-----------

(pwd)
==> "/home/nalaginrut/Project/gnulib-20100109+stable"

Any comment?