4. Shell Builtin Commands

4.1 Bourne Shell Builtins		Builtin commands inherited from the Bourne Shell.
4.2 Bash Builtin Commands		Table of builtins specific to Bash.
4.3 The Set Builtin		This builtin is so overloaded it deserves its own section.
4.4 Special Builtins		Builtin commands classified specially by POSIX.2.

Builtin commands are contained within the shell itself. When the name of a builtin command is used as the first word of a simple command (see section 3.2.1 Simple Commands), the shell executes the command directly, without invoking another program. Builtin commands are necessary to implement functionality impossible or inconvenient to obtain with separate utilities.

This section briefly the builtins which Bash inherits from the Bourne Shell, as well as the builtin commands which are unique to or have been extended in Bash.

Several builtin commands are described in other chapters: builtin commands which provide the Bash interface to the job control facilities (see section 7.2 Job Control Builtins), the directory stack (see section 6.8.1 Directory Stack Builtins), the command history (see section 9.2 Bash History Builtins), and the programmable completion facilities (see section 8.7 Programmable Completion Builtins).

Many of the builtins have been extended by POSIX or Bash.