1 files changed, 63 insertions, 0 deletions
diff --git a/m4/posix-shell.m4 b/m4/posix-shell.m4
new file mode 100644
index 0000000..dd7a0f6
--- /dev/null
+++ b/m4/posix-shell.m4
@@ -0,0 +1,63 @@
+# Find a POSIX-conforming shell.
+
+# Copyright (C) 2007-2022 Free Software Foundation, Inc.
+
+# This file is free software; the Free Software Foundation
+# gives unlimited permission to copy and/or distribute it,
+# with or without modifications, as long as this notice is preserved.
+
+# Written by Paul Eggert.
+
+# If a POSIX-conforming shell can be found, set POSIX_SHELL and
+# PREFERABLY_POSIX_SHELL to it.  If not, set POSIX_SHELL to the
+# empty string and PREFERABLY_POSIX_SHELL to '/bin/sh'.
+
+AC_DEFUN([gl_POSIX_SHELL],
+[
+  AC_CACHE_CHECK([for a shell that conforms to POSIX], [gl_cv_posix_shell],
+    [gl_test_posix_shell_script='
+       func_return () {
+         (exit [$]1)
+       }
+       func_success () {
+         func_return 0
+       }
+       func_failure () {
+         func_return 1
+       }
+       func_ret_success () {
+         return 0
+       }
+       func_ret_failure () {
+         return 1
+       }
+       subshell_umask_sanity () {
+         (umask 22; (umask 0); test $(umask) -eq 22)
+       }
+       test "[$](echo foo)" = foo &&
+       func_success &&
+       ! func_failure &&
+       func_ret_success &&
+       ! func_ret_failure &&
+       (set x && func_ret_success y && test x = "[$]1") &&
+       subshell_umask_sanity
+     '
+     for gl_cv_posix_shell in \
+         "$CONFIG_SHELL" "$SHELL" /bin/sh /bin/bash /bin/ksh /bin/sh5 no; do
+       case $gl_cv_posix_shell in
+         /*)
+           "$gl_cv_posix_shell" -c "$gl_test_posix_shell_script" 2>/dev/null \
+             && break;;
+       esac
+     done])
+
+  if test "$gl_cv_posix_shell" != no; then
+    POSIX_SHELL=$gl_cv_posix_shell
+    PREFERABLY_POSIX_SHELL=$POSIX_SHELL
+  else
+    POSIX_SHELL=
+    PREFERABLY_POSIX_SHELL=/bin/sh
+  fi
+  AC_SUBST([POSIX_SHELL])
+  AC_SUBST([PREFERABLY_POSIX_SHELL])
+])