[PATCH]: grep-default-command

[Haojun Bao]

the grep-default-command has problems in the sh-arg-re, that is, when
matching a double quoted thing, it can't handle correctly when there's
embedded double quote, like this: "x\"y". 

The old way to match a double quoted part is: 
    
    1) match a (beginning) double quote and go to 2)

    2) do the following

        2a) match anything not a double quote, go back to 2)
        2b) match an escape followed by a double quote, go back to 2)
      
       if it fails, go to 3).

    3) match a (ending) double quote

To improve it, 2a) and 2b) need switched. 



A second problem is when matching a non-quoted thing, the old way is:

  match anything not a quote (double/single) or a space (SPC, \t, \n)

And it won't handle the following: `aa\ bb', `aa|bb'. The first should
be considered a single arg, the second should not.

A more correct way should be:
    
    match an escape followed by anything, or 
    match non-special characters (not the meta-characters, like space, pipe, 
redirect, etc).


=== modified file 'lisp/progmodes/grep.el'
--- lisp/progmodes/grep.el      2010-05-21 20:43:04 +0000
+++ lisp/progmodes/grep.el      2010-08-14 16:11:37 +0000
@@ -628,7 +628,16 @@
   (let ((tag-default (shell-quote-argument (grep-tag-default)))
        ;; This a regexp to match single shell arguments.
        ;; Could someone please add comments explaining it?
-       (sh-arg-re "\\(\\(?:\"\\(?:[^\"]\\|\\\\\"\\)+\"\\|'[^']+'\\|[^\"' 
\t\n]\\)+\\)")
+
+        ;; Here's explanation: a shell arg can be a series of these 3 things:
+        ;;
+        ;; 1) Double quoted thing, in which double quote can occur, but must 
be led by the escape ?\\
+        ;; 2) Single quoted thing, in which anything except the single quote 
can occur
+        ;; 3) Non-quoted thing, in which some special chars can not occur, 
unless they are led by escape.
+        ;; 
+        ;; Trick is to get the correct number of escapes!
+
+       (sh-arg-re 
"\\(\\(?:\"\\(?:\\\\\"\\|[^\"]\\)+\"\\|'[^']+'\\|\\(?:\\\\.\\|[^\"' 
\\|><\t\n]\\)\\)+\\)")
        (grep-default (or (car grep-history) grep-command)))
     ;; In the default command, find the arg that specifies the pattern.
     (when (or (string-match