With this knowledge of what a command is, we can now search for the documentation available for each kind of command.
bash has a built-in help facility for each of the shell builtins. To use it, type
help followed by the name of the shell builtin. For example:
help cdcd: 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 ...