--- a/posix.rst	Thu Dec 23 00:12:42 2010 +0200
+++ b/posix.rst	Sun Jan 16 23:04:07 2011 +0200
@@ -7,3 +7,30 @@
 
   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