posix-string-match does not distinguish "*" from "*?"

posix-string-match does not distinguish "*" from "*?"

[Matt Swift]

`posix-string-match' (and I presume the other `posix-*' searching
functions) do not seem to distinguish between the "*" and "*?"
operators.  No mention is made of this difference from `string-match'
in the Elisp manual, which describes the posix- functions as having
super-greedy repetition constructs and handling of "|", but a reader
would not guess that these functions differ with respect to the
explicitly non-greedy operators "*?", "+?"  and "??".  Since I do not
have access to the POSIX specs, someone else will have to discern
whether this is a dox bug or a bug in `posix-string-match'.


This is the example from the manual description of the non-greedy operators:

(let ((s "cdaaada")
      (rshort "c[ad]*?a"))
  (list
   (progn
     (string-match rshort s)
     (match-string 0 s))
   (progn
     (posix-string-match rshort s)
     (match-string 0 s))
))

=> ("cda" "cdaaada")


node (elisp)POSIX Regexps: 

       The usual regular expression functions do backtracking when necessary
    to handle the `\|' and repetition constructs, but they continue this
    only until they find _some_ match.  Then they succeed and report the
    first match found.

       This section describes alternative search functions which perform the
    full backtracking specified by the POSIX standard for regular expression
    matching.  They continue backtracking until they have tried all
    possibilities and found all matches, so they can report the longest
    match, as required by POSIX.  This is much slower, so use these
    functions only when you really need the longest match.

Re: posix-string-match does not distinguish "*" from "*?"

[Andreas Schwab]

Matt Swift <swift@alum.mit.edu> writes:

|> `posix-string-match' (and I presume the other `posix-*' searching
|> functions) do not seem to distinguish between the "*" and "*?"
|> operators.  No mention is made of this difference from `string-match'
|> in the Elisp manual, which describes the posix- functions as having
|> super-greedy repetition constructs and handling of "|", but a reader
|> would not guess that these functions differ with respect to the
|> explicitly non-greedy operators "*?", "+?"  and "??".  Since I do not
|> have access to the POSIX specs, someone else will have to discern
|> whether this is a dox bug or a bug in `posix-string-match'.

POSIX does not define any of these non-greedy operators:

  The behavior of multiple adjacent duplication symbols ('+', '*', '?',
  and intervals) produces undefined results.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
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