--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/posix.rst	Mon Feb 22 12:46:36 2016 +0200
@@ -0,0 +1,45 @@
+.. -*- coding: utf-8; -*-
+.. include:: HEADER.rst
+
+=======
+ POSIX
+=======
+.. contents::
+   :local:
+
+Download POSIX
+==============
+
+  http://www.opengroup.org/onlinepubs/009695399/download
+                download page for SYSV3
+
+  http://www.opengroup.org/onlinepubs/9699919799/download
+                download page for SYSV4
+
+Shell command
+=============
+
+command
+-------
+
+Main semantic is to invoke command instead defined function with same name::
+
+  $ ls() { ls --color "$@"; }
+  $ ls                          # infinitely loop as func invoke itself
+  $ ls() { command ls --color "$@"; }
+  $ ls .                        # invoke /bin/ls with color output
+  $ unset ls                    # forget func definition
+  $ ls                          # invoke /bin/ls without color output
+
+With '-p' arg Perform the command search using a default value for PATH that
+is guaranteed to find all of the standard utilities::
+
+  $ command -p getconf PATH
+
+With '-v' arg work like 'which' command which not included in POSIX::
+
+  $ command -v ls
+  /usr/bin/ls
+  $ command -v echo             # for build-in command print command itself
+  echo                          # you can check for equality or for slash to
+                                # distinguish from utilities