command demo

bash-4.2$ which command
which: no command in (/usr/lib/jvm/java-7-openjdk/jre/bin:/usr/lib/jvm/java-7-openjdk/bin:/usr/lib/java/bin:/usr/lib/java/jre/bin:/usr/local/bin:/usr/bin:/bin)

bash-4.2$ date() { echo 'at the end of days...'; }

bash-4.2$ date
at the end of days...

bash-4.2$ command date
Mon Jan 21 17:56:16 EET 2013

bash-4.2$ dash

$ date() { echo 'at the end of days...'; }

$ date
at the end of days...

$ command date
Mon Jan 21 17:56:40 EET 2013

bash-4.2$ ksh

$ date() { echo 'at the end of days...'; }

$ date
at the end of days...

$ command date
Mon Jan 21 17:57:20 EET 2013

bash-4.2$ zsh

manatwork% date() { echo 'at the end of days...'; }

manatwork% date
at the end of days...

manatwork% command date
Mon Jan 21 17:57:45 EET 2013