Cleanup and improves readability of setuser

image/bin/setuser

@@ -1,26 +1,64 @@
 #!/usr/bin/python3
-import sys, os, pwd
+'''
+Copyright (c) 2013-2015 Phusion Holding B.V.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+'''
+
+import sys
+import os
+import pwd
 
-if len(sys.argv) < 3:
-	sys.stderr.write("Usage: /sbin/setuser USERNAME COMMAND [args..]\n")
-	sys.exit(1)
 
 def abort(message):
     sys.stderr.write("setuser: %s\n" % message)
     sys.exit(1)
 
-username = sys.argv[1]
-try:
+
+def main():
+    '''
+    A simple alternative to sudo that executes a command as a user by setting
+    the user ID and user parameters to those described by the system and then
+    using execvp(3) to execute the command without the necessity of a TTY
+    '''
+
+    username = sys.argv[1]
+    try:
         user = pwd.getpwnam(username)
-except KeyError:
+    except KeyError:
         abort("user %s not found" % username)
-os.initgroups(username, user.pw_gid)
-os.setgid(user.pw_gid)
-os.setuid(user.pw_uid)
-os.environ['USER'] = username
-os.environ['HOME'] = user.pw_dir
-os.environ['UID']  = str(user.pw_uid)
-try:
+    os.initgroups(username, user.pw_gid)
+    os.setgid(user.pw_gid)
+    os.setuid(user.pw_uid)
+    os.environ['USER'] = username
+    os.environ['HOME'] = user.pw_dir
+    os.environ['UID'] = str(user.pw_uid)
+    try:
         os.execvp(sys.argv[2], sys.argv[2:])
-except OSError as e:
+    except OSError as e:
         abort("cannot execute %s: %s" % (sys.argv[2], str(e)))
+
+if __name__ == '__main__':
+
+    if len(sys.argv) < 3:
+        sys.stderr.write("Usage: /sbin/setuser USERNAME COMMAND [args..]\n")
+        sys.exit(1)
+
+    main()
+