Set exit status on abcfield.py to indicate if anything found.

abcfield.py

@@ -130,6 +130,7 @@ def process(inf, options):
                 continue
             found = True
             print(convertField(line, options))
+    return found
 
 parser = optparse.OptionParser(usage="usage: %prog [options] [filename]\n\n"
                                      "  Extract field data from ABC file.")
@@ -148,13 +149,14 @@ parser.add_option("-s", "--starts", dest="starts",
                   metavar="CONTENT")
 (options, args) = parser.parse_args()
 
+res = False
 if len(args) > 0:
     for arg in args:
         try:
             inf = open(arg, "r")
-            process(inf, options)
+            res = res or process(inf, options)
         finally:
             inf.close()
 else:
-    process(sys.stdin, options)
-sys.exit(0)
+    res = process(sys.stdin, options)
+sys.exit(int(not res))