string-strip.el 1.1

;;; string-strip.el --- Strip CHARS from STRING

;; Version: 1.1

;; Copyright (C) 2007  Andreas Roehler

;; Author: Andreas Roehler <andreas.roehler@xxxxxxxxxxxxx>
;; Keywords: convenience

;; This file is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 2, or (at your option)
;; any later version.

;; This file is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs; see the file COPYING.  If not, write to
;; the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
;; Boston, MA 02110-1301, USA.

;;; Commentary:

;; Needed a function to correct user-input, i.e. wrongly inserted
;; white spaces at the end or the beginning.

;; Used `comment-string-strip' from Stefan Monier's
;; newcomment.el to that purpose, which worked fine so
;; far. However, it requires handling of three arguments,
;; where just one was sufficient in the cases I needed
;; it.

;; Meanwhile a discussion in emacs-devel took place, which was
;; helpful in many respects. You may view it at

;; http://comments.gmane.org/gmane.emacs.devel/55961

;; Lars Hansen <lists@xxxxxxx> provided a regexp for
;; the case, the string may be composed of (and
;; preserve) newlines. In the context given now set
;; `string-chars-preserve' to "\\(\\(?:.\\|\n\\)*?\\)"
;; if you need this.

;; Finally I found it useful, not just to make the ends
;; customizable, but the middle part too: Now its
;; completely up to the user to decide, what the string
;; should contain and what chars are to strip from it.

;; (string-strip " foo   ") -> "foo"
;; shows the default-behavior

;; You may specify args on the fly, which will override it, thus

;; (string-strip "[:blank:]" "\\[:" ":\\]") -> "blank"  
;; (string-strip "[:blank:]" "\\[:.*" ":\\]" "\\(a.+\\)") -> "ank"  

;; Changes to previous version:

;; Let optional arguments overrid defaults, interactive
;; spec dropped as it seems not useful, Doku renewed

;;; Code:

;; (setq strip-chars-before  "[ \t\r\n\f]*")
(defcustom strip-chars-before  "[ \t\r\n\f]*"
"Regexp indicating which chars shall be stripped before STRING - which 
is defined by `string-chars-preserve'"

:type 'string
:group 'convenience)

;; (setq strip-chars-after  "[ \t\r\n\f]*")
(defcustom strip-chars-after  "[ \t\r\n\f]*\\'"
 "Regexp indicating which chars shall be stripped after STRING - which 
is defined by `string-chars-preserve'"

:type 'string
:group 'convenience)

;; (setq string-chars-preserve  "\\(\\(?:.\\|\n\\)*?\\)"
(defcustom string-chars-preserve  "\\(.*?\\)"
   "Parentized regexp indicating which chars shall be constitutes of STRING
thus being preserved - whereas `strip-chars-after' and
`strip-chars-before' indicate what class of chars to strip from 
beginning or end of STRING
You may customize this variable. For Example if your string to preserve 
may include newlines, use \"\\(\\(?:.\\|\n\\)*?\\)\""

:type 'string
:group 'convenience)

(defun string-strip (str &optional chars-before chars-after chars-preserve)
 "Return a copy of STR with leading and trailing CHARS removed.
If no regexp for `chars-before' `chars-after' `chars-preserve' are 
specified,
defaults of `strip-chars-before' and `strip-chars-after' 
`string-chars-preserve' are used instead.  
`strip-chars-before' and `strip-chars-after' default is \"[ \t\r\n\f]*\",  
i.e. spaces, tabs, carriage returns, newlines and newpages.
`string-chars-preserve' must be a parentized expression,
it defaults to \"\\(.*?\\)\""
 (save-match-data
   (let ((s-c-b (or chars-before
            strip-chars-before))
     (s-c-a (or chars-after
            strip-chars-after))
     (s-c-p (or chars-preserve
            string-chars-preserve)))
     (string-match
      (concat "\\`" s-c-b s-c-p s-c-a "\\'") str)
     (match-string  1 str))))

(provide 'string-strip)
;;; string-strip.el ends here