added support for command execution

variable_grabbler.py

@@ -1,14 +1,32 @@
 #!/usr/bin/python2
 
 print """
-Variable Grabbler - version 3.3
+Variable Grabbler - version 3.4
 -------------------------------"""
+################################################################
+# Changes in this version:
+#===============================================================
+# * added support for command execution
+# * some internal technicalities that should not impact features
+# * Yes.
+#
+
+################################################################
+# Exit codes:
+#===============================================================
+# 0 => normal exit
+# 1 => argument error
+# 2 => error while processing
+#
 
 # definitions
-import os, json, sys
+import os, json, sys, subprocess
+
+def print_err(text):
+  print >> sys.stderr, text
 
 if not len(sys.argv)==3:
-  print >> sys.stderr, "Error: Exactly two arguments required: \"python variable_grabbler.py <file to be rewritten> <config file>\""
+  print_err("Error: Exactly two arguments required: \"python variable_grabbler.py <file to be rewritten> <config file>\"")
   sys.exit(1)
 
 print "Reading config file...",
@@ -30,9 +48,21 @@ for variable in config_values:
     file_replacement.close()
   elif config_values[variable][0] == "exec":
     print "Found array. Executing command instead: " + config_values[variable][1]
-    #Add code to replace variable with command output here
+    process = subprocess.Popen(config_values[variable][1], shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
-    print >> sys.stderr, "Error: This option is not yet supported."
+    stdout, stderr = process.communicate()
-    replacement = ""
+    if process.returncode == 0:
+      print "Process exited normally. Replacing variable with the output from STDOUT..."
+      print_err("Subprocess exited normally.\nThe following error messages were produced:")
+      print_err(stderr)
+      replacement = stdout
+    else:
+      print "Process exited abnormally. Exiting. No changes will be made."
+      print_err("Subprocess exited abnormally. Exiting.\nThe following output was produced:")
+      print_err(stdout)
+      print_err("The following error messages were produced:")
+      print_err(stderr)
+      print "Exiting now."
+      sys.exit(2)
   else:
     replacement = config_values[variable]
     print repr(replacement)