configure: detect more good shells.

* configure: There is a clue in the PS2 and PS4 variables.
If these are present and have the values "> " and "+ "
the shell could be Dash or newer NetBSD Ash, which
got PS4 circa 2004. The Solaris XPG shell also has these.

1 files changed, 7 insertions, 0 deletions

diff --git a/configure b/configure
index 2f78a8af..8ba00895 100755
--- a/configure
+++ b/configure
@@ -49,6 +49,13 @@ while true ; do
     break
   fi
 
+  # If the shell has PS2 and PS4 with these values, it is
+  # probably a good shell: late-model Ash, Dash or the XPG
+  # shell on Solaris and perhaps others.
+  if test "x$PS2" = "x> " && test "x$PS4" = "x+ " ; then
+    break
+  fi
+
   # Slow path: find a suitable shell.
   # First choice is $CONFIG_SHELL, a convention from GNU Autoconf.
   for shell in "$CONFIG_SHELL" \