1 files changed, 54 insertions, 0 deletions
diff --git a/m4/diff.m4 b/m4/diff.m4
new file mode 100644
index 0000000..87b5d13
--- /dev/null
+++ b/m4/diff.m4
@@ -0,0 +1,54 @@
+dnl file      : m4/diff.m4
+dnl copyright : Copyright (c) 2009-2013 Code Synthesis Tools CC
+dnl license   : MIT; see accompanying LICENSE file
+dnl
+dnl DIFF_TOOL
+dnl
+AC_DEFUN([DIFF_TOOL], [
+diff_found=no
+
+AC_ARG_VAR([DIFF],[diff command])
+AC_ARG_VAR([DIFFFLAGS],[diff flags])
+
+AC_ARG_WITH(
+  [diff],
+  [AC_HELP_STRING([--with-diff=PATH],[path to the diff program])],
+  [diff_path=${withval}],
+  [diff_path=])
+
+AC_MSG_CHECKING([for diff])
+
+if test x"$DIFF" = x; then
+ if test x"$diff_path" != x; then
+   AS_SET_CATFILE([abs_diff_path], [$ac_pwd], [$diff_path])
+   DIFF="$abs_diff_path"
+ else
+   DIFF=diff
+ fi
+fi
+
+cat >conftest.txt
+
+$DIFF conftest.txt conftest.txt 2>/dev/null 1>&2
+
+if test x"$?" = x0; then
+  AC_MSG_RESULT([$DIFF])
+else
+  AC_MSG_RESULT([no])
+  AC_MSG_ERROR([diff command is not found; consider setting the DIFF variable or using --with-diff=PATH])
+fi
+
+AC_MSG_CHECKING([whether $DIFF accepts -u])
+
+$DIFF -u conftest.txt conftest.txt 2>/dev/null 1>&2
+
+if test x"$?" = x0; then
+  AC_MSG_RESULT([yes])
+  DIFFFLAGS="$DIFFFLAGS -u"
+else
+  AC_MSG_RESULT([no])
+fi
+
+rm -f conftest.txt
+
+])dnl