enhance scripts/activate-global-python-argcomplete (#461)

* automatically answer yes for all questions

* avoid repeatedly appending to configuration files

scripts/activate-global-python-argcomplete

@@ -81,6 +81,11 @@ def install_to_destination(dest):
 
 
 def get_consent():
+    try:
+        if args.yes is True:
+            return True
+    except NameError:
+        pass
     while True:
         res = input("OK to proceed? [y/n] ")
         if res.lower() not in {"y", "n", "yes", "no"}:
@@ -93,6 +98,10 @@ def get_consent():
 
 def append_to_config_file(path, shellcode):
     if os.path.exists(path):
+        with open(path, 'r') as fh:
+            if shellcode in fh.read():
+                print(f"The code already exists in the file {path}.", file=sys.stderr)
+                return
         print(f"argcomplete needs to append to the file {path}. The following code will be appended:", file=sys.stderr)
         for line in shellcode.splitlines():
             print(">", line, file=sys.stderr)
@@ -115,6 +124,7 @@ def link_user_rcfiles():
 
 
 parser = argparse.ArgumentParser(description=__doc__, formatter_class=argparse.RawDescriptionHelpFormatter)
+parser.add_argument("-y", "--yes", help="automatically answer yes for all questions", action="store_true")
 parser.add_argument("--dest", help='Specify the shell completion modules directory to install into, or "-" for stdout')
 parser.add_argument("--user", help="Install into user directory", action="store_true")
 argcomplete.autocomplete(parser)