The which command

• Before you run a command, which tells you where it is found

• bash> which ls alias ls='ls --color=tty' /bin/ls

• tcsh> which ls ls: aliased to ls --color=tty

• bash> which alias /usr/bin/which: no alias in (/usr/local/bin:/usr/bin:/bin:/usr/X11R6/bin)

• tcsh> which alias alias: shell built-in command.