Re: sed: portability of $ in pattern (Was: Re: [PATCH] Speedup creation of configure.lineno)

[Paul Eggert]

Alexandre Duret-Lutz <address@hidden> writes:

>   ac_i=`echo "$ac_i" |
>          sed 's/\$U\././;s/\.o$//;s/\.obj$//'`
> 
> Inside back-quotes, \ is active only before $ and `,
> so the command actually run in the sub-shell is 
> 
>   echo "$ac_i" | sed 's/$U\././;s/\.o$//;s/\.obj$//'
> 
> Note the $U which ought to be a [$]U.

Aack.  This is a confusing area, and I suspect (without being able to
prove it) that we can't rely on POSIX semantics here.  I installed
this patch, which uses my usual workaround for this sort of problem.

2004-01-07  Paul Eggert  <address@hidden>

        * lib/autoconf/general.m4 (_AC_LIBOBJS_NORMALIZE): Avoid \$ inside
        `"'...'"`, as it's confusing (and I suspect it may not work on
        some platforms).  The code was incorrect anyway, as it assumed
        that \$ evaluated to itself in that context.  Reported by
        Alexandre Duret-Lutz.

--- general.m4.~1.826.~ Sun Jan  4 22:19:09 2004
+++ general.m4  Wed Jan  7 15:46:43 2004
@@ -2445,8 +2445,8 @@ AC_DEFUN([_AC_LIBOBJS_NORMALIZE],
 ac_ltlibobjs=
 for ac_i in : $LIB@&address@hidden; do test "x$ac_i" = x: && continue
   # 1. Remove the extension, and $U if already installed.
-  ac_i=`echo "$ac_i" |
-        sed 's/\$U\././;s/\.o$//;s/\.obj$//'`
+  ac_script='s/\$U\././;s/\.o$//;s/\.obj$//'
+  ac_i=`echo "$ac_i" | sed "$ac_script"`
   # 2. Add them.
   ac_libobjs="$ac_libobjs $ac_i\$U.$ac_objext"
   ac_ltlibobjs="$ac_ltlibobjs $ac_i"'$U.lo'


> >>> "Paul" == Paul Eggert <address@hidden> writes:
>  >> +   /$LINENO/=' <$as_myself |
> 
>  Paul> For portability the $ needs to be escaped from 'sed' by
>  Paul> surrounding it with square brackets, which in turn need
>  Paul> to be doubled, thus: [[$]]LINENO.
>
> Any idea where it does not work?

Sorry, no.