echo $SHELL : default shell
uname: print current operation system information
df : disk free space information
!! : repeat last command
!$ : last argument
!partial_text : run history command by text
history : show command history
fc -l : show command history
set -o vi : use vi keybinding
<command> & : run at background
转载于:https://www.cnblogs.com/wangyh/archive/2009/04/17/some-shell-commands-1.html