This warning is annoying:
$ gexpr "foobarnone" : '^foo'
gexpr: warning: unportable BRE: `^foo': using `^' as the first character
of the basic regular expression is not portable; it is being ignored
3
Even worse is the fact that this warning is *WRONG*.
>From the original Seventh Edition Unix manual we can see that the claim
made by GNU expr is not documented there:
expr : expr
The matching operator compares the string first
argument with the regular expression second argu-
ment; regular expression syntax is the same as that
of ed(1). The \(...\) pattern symbols can be used
to select a portion of the first argument. Other-
wise, the matching operator yields the number of
characters matched (`0' on failure).
Examination of the original V7 (and 32V and SysIII) source for expr (or
regexp.h) also reveals that no such implicit '^' anchor implied either
-- the original code explicitly tests for a '^' anchor and the
expression is considered unanchored unless a leading '^' is explicitly
given.
I.e. modern versions of expr are *NOT* compatible with V7 (or 32V or
AT&T SysIII) and a portable script *MUST* use a '^' to explicitly anchor
the expression.
I think this change first appears in SysVr2.2, and I believe (IIRC) that
it was introduced as a side-effect of trying to use the newer "SysV"
regexp(3), and instead of fixing it they just documented it. (I
personally still think an unanchored RE would be more useful but I
confess I've not currently any scripts that would require it, partly
because I do most of my work on NetBSD these days with its public domain
1003.2 compliant version.)
The implicit anchor is documented in AT&T SysVr2.2, Tenth Edition,
NetBSD, GNU expr, and of course IEEE POSIX 1003.2.
(The so-called rationale in the P1003.2 draft is very irrational on this
topic though -- obviously none of the committee knew, or at least spoke
up about, the true history of expr and why the so-called "broken"
implementations differed from their documentation). What I'd like to do
is prevent GNU expr from promoting this false history too! I do have
lots of scripts that use a '^' anchor just to be safe and portable and
the GNU expr warning is a real pain.
--
Greg A. Woods
+1 416 218-0098 VE3TCP <[EMAIL PROTECTED]> <robohack!woods>
Planix, Inc. <[EMAIL PROTECTED]>; Secrets of the Weird <[EMAIL PROTECTED]>
