smurf: configmeld now issues a warning if meld is not available

applications/smurf/scripts/configmeld.py

@@ -12,8 +12,8 @@
 *     python (2.7 or 3.*)
 
 *  Description:
-*     This script use the unix meld tool to display two sets of
-*     configuration parameters, highlighting the differences between
+*     This script use the unix meld tool (see meldmerge.org) to display two
+*     sets of configuration parameters, highlighting the differences between
 *     them. Each config may be supplied directly, as is done when running
 *     MAKEMAP, or can be read from the History component of an NDF that
 *     was created by MAKEMAP.
@@ -45,7 +45,8 @@
 
 *  Notes:
 *     - The unix "meld" command must be installed and available on the
-*     unix PATH.
+*     unix PATH. If not already installed, it can be obtained from
+*     "meldmerge.org".
 
 *  Copyright:
 *     Copyright (C) 2013 Science & Technology Facilities Council.
@@ -100,6 +101,11 @@ def cleanup():
    except:
       pass
 
+# First check that "meld" ia available.
+if starutil.which( "meld" ) == None:
+   print( "\n!! The 'configmeld'  command uses the Unix 'meld' command, but "
+          "meld appears not to be installed. See 'meldmerge.org'.\n" )
+   os._exit(1)
 
 #  Catch any exception so that we can always clean up, even if control-C
 #  is pressed.

applications/smurf/scripts/starutil.py

@@ -24,6 +24,7 @@
 
 
 
+#  -------------------  misc ---------------------------
 
 #  Function to return the name of the executing script, without any
 #  trailing ".py" suffix.
@@ -36,12 +37,49 @@ def cmd():
       __cmd = __cmd[:-3]
    return __cmd
 
+
 #  "Protected" function to return the name of the executing script,
 #  followed by a colon and a space.
 def _cmd_token():
    return "{0}: ".format(cmd())
 
 
+def which(program):
+   """
+
+   This command mimics the UNix 'which' command. It searches the PATH for
+   a named commadn and returns the full path to the executable if found, and
+   None otherwise.
+
+   Invocation:
+      which(command)
+
+   Arguments:
+      command = string
+         The commmand to find
+
+   Returned Value:
+      The full path to the executable, or None of the executanble is not
+      found.
+
+   """
+
+   def is_exe(fpath):
+      return os.path.isfile(fpath) and os.access(fpath, os.X_OK)
+
+   fpath, fname = os.path.split(program)
+   if fpath:
+      if is_exe(program):
+         return program
+   else:
+      for path in os.environ["PATH"].split(os.pathsep):
+          path = path.strip('"')
+          exe_file = os.path.join(path, program)
+          if is_exe(exe_file):
+             return exe_file
+
+   return None
+