diff --git a/tools/require_tool.sh b/tools/require_tool.sh
new file mode 100755
index 00000000..42da2ccf
--- /dev/null
+++ b/tools/require_tool.sh
@@ -0,0 +1,161 @@
+__require_tool_version_compare ()
+{
+  (
+    # Locally ignore failures, otherwise we'll exit whenever $1 and $2
+    # are not equal!
+    set +e
+
+awk_strverscmp='
+  # Use only awk features that work with 7th edition Unix awk (1978).
+  # My, what an old awk you have, Mr. Solaris!
+  END {
+    while (length(v1) || length(v2)) {
+      # Set d1 to be the next thing to compare from v1, and likewise for d2.
+      # Normally this is a single character, but if v1 and v2 contain digits,
+      # compare them as integers and fractions as strverscmp does.
+      if (v1 ~ /^[0-9]/ && v2 ~ /^[0-9]/) {
+	# Split v1 and v2 into their leading digit string components d1 and d2,
+	# and advance v1 and v2 past the leading digit strings.
+	for (len1 = 1; substr(v1, len1 + 1) ~ /^[0-9]/; len1++) continue
+	for (len2 = 1; substr(v2, len2 + 1) ~ /^[0-9]/; len2++) continue
+	d1 = substr(v1, 1, len1); v1 = substr(v1, len1 + 1)
+	d2 = substr(v2, 1, len2); v2 = substr(v2, len2 + 1)
+	if (d1 ~ /^0/) {
+	  if (d2 ~ /^0/) {
+	    # Compare two fractions.
+	    while (d1 ~ /^0/ && d2 ~ /^0/) {
+	      d1 = substr(d1, 2); len1--
+	      d2 = substr(d2, 2); len2--
+	    }
+	    if (len1 != len2 && ! (len1 && len2 && substr(d1, 1, 1) == substr(d2, 1, 1))) {
+	      # The two components differ in length, and the common prefix
+	      # contains only leading zeros.  Consider the longer to be less.
+	      d1 = -len1
+	      d2 = -len2
+	    } else {
+	      # Otherwise, compare as strings.
+	      d1 = "x" d1
+	      d2 = "x" d2
+	    }
+	  } else {
+	    # A fraction is less than an integer.
+	    exit 1
+	  }
+	} else {
+	  if (d2 ~ /^0/) {
+	    # An integer is greater than a fraction.
+	    exit 2
+	  } else {
+	    # Compare two integers.
+	    d1 += 0
+	    d2 += 0
+	  }
+	}
+      } else {
+	# The normal case, without worrying about digits.
+	if (v1 == "") d1 = v1; else { d1 = substr(v1, 1, 1); v1 = substr(v1,2) }
+	if (v2 == "") d2 = v2; else { d2 = substr(v2, 1, 1); v2 = substr(v2,2) }
+      }
+      if (d1 < d2) exit 1
+      if (d1 > d2) exit 2
+    }
+  }
+'
+    awk "$awk_strverscmp" v1="$1" v2="$2" /dev/null
+    case $? in
+      1)  echo '<';;
+      0)  echo '=';;
+      2)  echo '>';;
+    esac
+  )
+}
+
+
+__require_tool_fatal ()
+{
+    echo $@ >/dev/stderr
+    return 1
+}
+
+# Usage: require_tool program version
+# Returns: 0 if $1 version if greater equals than $2, 1 otherwise.
+# In case of error, message is written on error output.
+#
+# Example: require_tool gcc 4.6
+# Use GCC environment variable if defined instead of lookup for the tool
+# in the environment.
+require_tool ()
+{
+  envvar_name=$(echo $1 | tr '[:lower:]' '[:upper:]')
+  tool=$(printenv $envvar_name || echo $1)
+  local version=$($tool --version 2>/dev/null| \
+    sed -n 's/.*[^0-9.]\([0-9][0-9.]*\).*/\1/p;q')
+  if test x"$version" = x ; then
+      echo "$tool is required" >/dev/stderr
+      return 1
+  fi
+  case $(__require_tool_version_compare "$2" "$version") in
+    '>')
+	  echo "$1 $2 or better is required: this is $tool $version" >/dev/stderr
+	  return 1
+	  ;;
+  esac
+}
+
+usage() {
+    cat <<EOF
+NAME
+    require_tool.sh - Ensure version of a tool is greater than the one expected
+
+SYNOPSYS
+    require_tool.sh [ -h ]
+                    [ --help ]
+                    [ TOOL MIN_VERSION ]
+
+DESCRIPTION
+    TOOL is the name or path of the program to check. If the name is specified, its
+    path is deduced from PATH environment variable. If environment variable TOOL
+    (in upper-case characters) is defined, considers its value as path to the tool.
+
+    MIN_VERSION is a string representing the minimum required version.
+
+BEHAVIOR
+    * locate path to the program.
+    * execute $ TOOL_PATH --version
+    * extract version from standard output.
+    * compare this version to the expected one.
+
+OPTIONS
+    -h --help
+        Display this message and exit 0
+
+ERRORS
+    if program is not found or its version is prior to expected version,
+    a message is written to error output.
+
+EXIT VALUE
+    returns 0 if program version if greater equals than expected version,
+    returns 1 otherwise.
+
+EXAMPLE
+    $ require_tool.sh emacs 23
+    $ CC=g++ require_tool.sh cc 4.6
+    $ require_tool.sh zsh 4.5
+
+EOF
+}
+
+for arg in $@; do
+    case $arg in
+        -h|--help)
+            usage
+            exit 0
+            ;;
+    esac
+done
+if [ $# -gt 2 ] ; then
+    echo "ERROR: expecting 2 parameters. Please see option --help"
+    exit 1
+fi
+
+require_tool $@