Builtin commands are always kinda’ interesting. At first glance, it’s hard to know which commands are builtins. Luckily, there’s a command that I rarely use, called… command. If you run command with the -V flag it will tell you if the command is a builtin:
command -V cd
cd is a shell builtin
If you run a command that isn’t a builtin
command -V ls
ls is /bin/ls
Some builtins are in /bin (like echo). But not all builtins are in /bin. Some are in /usr/bin (like cd). Information about how to use builtins is built into the help command rather than standalone man pages. So, if you do help followed by the name of a command, you’ll get information about the command, and sometimes how to use the command:
help cd
cd: cd [-L|-P] [dir]
Change the current directory to DIR. The variable $HOME is the
default DIR. The variable CDPATH defines the search path for
the directory containing DIR. Alternative directory names in CDPATH
are separated by a colon (:). A null directory name is the same as
the current directory, i.e. `.’. If DIR begins with a slash (/),
then CDPATH is not used. If the directory is not found, and the
shell option `cdable_vars’ is set, then try the word as a variable
name. If that variable has a value, then cd to the value of that
variable. The -P option says to use the physical directory structure
instead of following symbolic links; the -L option forces symbolic links
to be followed.
There are also commands not in a path, which can be found using the which command:
which dsconfigad
/usr/sbin/dsconfigad