chgrp: Move --from argument parsing logic to core module

This prevents duplication when it has to be used in some other future
utilities such as chown. Also added support for numeric UIDs/GIDs
instead of only accepting user/group names.

Author: Expertcoderz

userland/core/__init__.py

@@ -1,2 +1,3 @@
 from .command import *
 from .io import *
+from .users import *

userland/core/users.py

@@ -0,0 +1,38 @@
+import grp
+import pwd
+
+from optparse import OptionParser
+
+
+def parse_onwer_spec(
+    parser: OptionParser, owner_spec: str
+) -> tuple[int | None, int | None]:
+    """
+    Process a string in the form ``[USER][:GROUP]`` and return the UID and GID.
+    Either or both may be None if omitted from the input string.
+    An appropriate parser error is thrown if obtaining the UID or GID fails.
+    """
+    tokens = owner_spec.split(":")
+
+    uid: int | None = None
+    gid: int | None = None
+
+    if tokens[0]:
+        if tokens[0].isdecimal():
+            uid = int(tokens[0])
+        else:
+            try:
+                uid = pwd.getpwnam(tokens[0])
+            except KeyError:
+                parser.error(f"invalid user: '{tokens}'")
+
+    if len(tokens) > 1 and tokens[1]:
+        if tokens[1].isdecimal():
+            gid = int(tokens[1])
+        else:
+            try:
+                gid = grp.getgrnam(tokens[1])
+            except KeyError:
+                parser.error(f"invalid group: '{tokens}'")
+
+    return uid, gid

userland/utilities/chgrp.py

@@ -135,19 +135,7 @@ def python_userland_chgrp(opts, args):
     from_gid: int | None = None
 
     if opts.from_spec:
-        from_spec = opts.from_spec.split(":")
-
-        if from_spec[0]:
-            try:
-                from_uid = pwd.getpwnam(from_spec[0])
-            except KeyError:
-                parser.error(f"invalid user: '{opts.from_spec}'")
-
-        if len(from_spec) > 1 and from_spec[1]:
-            try:
-                from_gid = grp.getgrnam(from_spec[1])
-            except KeyError:
-                parser.error(f"invalid group: '{opts.from_spec}'")
+        from_uid, from_gid = core.parse_onwer_spec(parser, opts.from_spec)
 
     gid: int
     gname: str | None = None