A builtin is a utility (also called a command) that is built into a shell. Each of the shells has its own set of builtins. When it runs a builtin, the shell does not fork a new process. Consequently builtins run more quickly and can affect the environment of the current shell. Because builtins are used in the same way as utilities, you will not typically be aware of whether a utility is built into the shell or is a stand-alone utility.
For example, echo is a shell builtin. It is also a stand-alone utility. The shell always executes a shell builtin before trying to find a command or utility with the same name. See page 1062 for an in-depth discussion of builtin commands and page 1077 for a list of bash builtins.
Listing bash builtins
To display a list of bash builtins, give the command info bash shell builtin. To display a page with information on each builtin, move the cursor to the Bash Builtins line and press RETURN. Alternately, you can view the builtins man page.
Getting help with bash builtins
You can use the bash help command to display information about bash builtins. See page 141 for more information.