ax_sys_perlsharpbang

Determine how the perl interpreter is located by the OS kernel and make substitution variable PERL_SHEBANG available. Does AC_PATH_PROG to find the path to perl. As a side-effect, that sets PERLINTERP and makes it available as a substitution variable.

Note: The macro allows for the possibility (expected to be seldom used) of an explicit user override (the "user" being the operator executing the final 'configure' script, in this context) by making the option argument like:

    --with-perl-shebang='#! /my/funky/perlpath' # OR
    --with-perl-shebang='/my/funky/perlpath'  # we just throw away the #! anyway
                                              # bec it must be absent in Makefile

Rationale: The are various ways of starting an interpreter on different *nix-like systems. Many use the simple

   #!/usr/bin/perl

but it could be instead

   #!/usr/local/bin/perl

and there is even the possibility that the user wants

   #!/usr/bin/env perl

to find whichever perl comes first in the current $PATH. This is preferred by some of us because we run multiple perl installations on the same box. Adjusting our $PATH then allows us to set precedence over other perls, even whatever the "house" version is.

Users on very non-unix systems like MS Windows do not have a kernel that does this kind of thing from the first line of script files, but instead the perl on their machine is started and merely notices whatever comes after the interpreter path on this first line of the script (options like "-w").

Acknowledgement: this macro was inspired in part by <ac_prog_perl_version> authored by Dean Povey, see the AC-Archive (ac-archive.sf.net).

AC_DEFUN([AX_SYS_PERLSHARPBANG],[dnl

   AC_PATH_PROG(PERLINTERP,perl,perl)
   ac_cv_path_perlinterp="$PERLINTERP"
   _sHpB='#!'

   AC_ARG_WITH(perl-shebang,
                AC_HELP_STRING([--with-perl-shebang],
           [override what perl thinks is the way for the kernel to start it (seldom needed)]dnl
		           ),
		[opt_perl_shebang="$withval"]dnl
		            ,dnl
		[opt_perl_shebang="not_set"]dnl
    )dnl

   AC_CACHE_CHECK([whether explicit instead of detected sharpbang is to be used],
		   ax_cv_opt_perl_shebang,
		  [ case "$opt_perl_shebang" in
		      not_set  ) ax_cv_opt_perl_shebang=''
		               ;;
		         *     )
	ax_cv_opt_perl_shebang=`echo "$opt_perl_shebang" | sed -e's|^#!\s*\(.*\)$|\1|'`
		    esac
		  ]dnl
    )dnl

   if test "A$ax_cv_opt_perl_shebang" != "A"
     then
       ac_cv_sys_kernshrpbang_perl="$ax_cv_opt_perl_shebang"
       PERL_SHEBANG="$ac_cv_sys_kernshrpbang_perl"
       AC_SUBST(PERL_SHEBANG)dnl
       AC_MSG_NOTICE([OK - PERL_SHEBANG is $_sHpB$PERL_SHEBANG.])

# Automatic detection of sharpbang formula starts here
     else dnl

   _somian_shbangperl=`$PERLINTERP -V:startperl`
   negclass="[[^']]"; dnl
# must leave this comment:  m4 will remove the outer brackets for us, heheh
   AC_CACHE_CHECK([for kernel sharpbang invocation to start perl],
	          ac_cv_sys_kernshrpbang_perl,
	[_somian_kspb_perl=`echo "$_somian_shbangperl" | sed -ne"s|.*='\($negclass*\)';$|\1|p"`
	if test "x$_somian_kspb_perl" == x
	  then _somian_ksbp_warn_empty='durnit'
	  else
	  case "A$_somian_kspb_perl" in
	         A#!*perl* )
           ac_cv_sys_kernshrpbang_perl=`echo "$_somian_kspb_perl" | sed -e's|#!\(.*\)$|\1|'`
			;;
	             A*    )  _somian_ksbp_warn_defau='trouble'
		              ac_cv_sys_kernshrpbang_perl="$PERLINTERP"
	  esac
	fi
])dnl Done with testing sharpbang

# The above prints Checking ... result message to user.
   PERL_SHEBANG="$ac_cv_sys_kernshrpbang_perl"
   AC_SUBST(PERL_SHEBANG)
    if test A${_somian_ksbp_warn_empty+set} == Aset
      then   AC_MSG_WARN([dnl
In last check, doing $PERLINTERP -V:startperl yielded empty result! That should not happen.])
    fi
# Inform user after printing result value
    if test A${_somian_ksbp_warn_defau+set} == Aset
      then AC_MSG_NOTICE([Maybe Not good -])
	   AC_MSG_WARN([dnl
In last check perl's Config query did not work so we bunted: $_sHpB$PERLINTERP])
      else AC_MSG_NOTICE([OK Good result - ])
	   AC_MSG_NOTICE([dnl
In last check we got a proper-looking answer from perl's Config: $_somian_shbangperl])
dnl Done with user info messages
    fi
dnl Outer loop checked for user override term here
  fi dnl

])dnl EOMACRO DEF