Re: Why is this "quadrigraph" necessary?

[Bert Wesarg]

Hi,

On Sun, Nov 23, 2014 at 10:38 PM, Bruce Korb <address@hidden> wrote:
>
> AC_DEFUN([INVOKE_AG_MACROS_LAST],[
> [if test X${INVOKE_AG_MACROS_LAST_done} != Xyes ; then]
>   GUILE_FLAGS
>   [ag_gv=$( exec 2>/dev/tty ; set -x
>   gdir=$(pkg-config --cflags-only-I guile-${GUILE_EFFECTIVE_VERSION})
>   gdir=$(echo ${gdir#-I})
>   gdir=$(awk '/SCM_MICRO_VERSION/{ print @S|@3 }'
> ${gdir}/libguile/version.h)
>   printf '%u%02u%03u' ${GUILE_EFFECTIVE_VERSION%\.*}
> ${GUILE_EFFECTIVE_VERSION#*\.} ${gdir}
>   )]
>
> If I change that "@S|@" thingy to "$" it and the following "3" disappear.
> Why?

Because '$3' will be recognize by M4 as a parameter. It will be
replaced by the third argument to INVOKE_AG_MACROS_LAST. Thus it needs
quoting, be it by "@S|@" or "$[]3"
 does not matter though.

Bert

> (And, yes, this fragment only works on recent POSIX shells.)
>