Shell Builtins

Built-in commands are distinct in that they do not require the execution of a child process. They were compiled into the shell and thus become part of its toolkit. There is no external program file to run them.

Bash Built‐In Commands #-B

Command	Description
`.`	same as `source` builtin. Reads and executes commands from a designated file in the current shell
`&`	Starts a job in background mode
`((x))`	Evaluates the x mathematical expression
`not:`	Reads and executes commands from a designated file in the
current shell.
`:`	Does nothing, and always exits successfully, same as `true` builtin
`[ t ]`	Evaluates the t conditional expression
`[[ e ]]`	Evaluates the e conditional expression
`alias`	Defines an alias for the specified command
`bg`	Resumes a job in background mode
`bind`	Binds a keyboard sequence to a readline function or macro
`break`	Exits from a for , while , select , or until loop
`builtin`	Executes the specified shell built‐in command

Bash Built‐In Commands E-F

`echo`	Displays the specified string to STDOUT
`enable`	Enables or disables the specified built‐in shell command
`eval`	Concatenates the specified arguments into a single command, and executes the command
`exec`	Replaces the shell process with the specified command
`exit`	Forces the shell to exit with the specified exit status
`export`	Sets the specified variables to be available for child shell processes
`false`	Sets a result to failed status
`fc`	Selects a list of commands from the history list
`fg`	Resumes a job in foreground mode
`for`	Executes set commands for every item in the list
`function`	Defines a shell script function

Bash Built‐In Commands G-P

`getopts`	Parses the specified positional parameters
`hash`	Finds and remembers the full pathname of the specified command
`help`	Displays a help file
`history`	Displays the command history
`if`	Executes set commands based on conditional expression
`jobs`	Lists the active jobs
`kill`	Sends a system signal to the specified process ID (PID)
`let`	Evaluates each argument in a mathematical expression
`local`	Creates a limited‐scope variable in a function
`logout`	Exits a login shell
`mapfile`	Reads STDIN lines and puts them into an indexed array
`popd`	Removes entries from the directory stack
`printf`	Displays text using formatted strings
`pushd`	Adds a directory to the directory stack
`pwd`	Displays the pathname of the current working directory

Bash Built‐In Commands C-D

`caller`	Returns the context of any active subroutine call
`case`	Selectively executes commands based on pattern
`cd`	Changes the current directory to the specified directory
`command`	Executes the specified command without the normal shell lookup
`compgen`	Generates possible completion matches for the specified word
`complete`	Displays how the specified words would be completed
`compopt`	Changes options for how the specified words would be completed
`continue`	Resumes the next iteration of a for , while , select , or until loop
`coproc`	Executes a coprocess
`declare`	Declares a variable or variable type
`dirs`	Displays a list of currently remembered directories
`disown`	Removes the specified jobs from the jobs table for the process

Bash Built‐In Commands R-#

`read`	Reads one line of data from STDIN , and assigns it to a variable
`readarray`	Reads STDIN lines, and puts them into an indexed array
`readonly`	Reads one line of data from STDIN , and assigns it to a variable that can't be changed
`return`	Forces a function to exit with a value that can be retrieved by the calling script
`select`	Displays list of words with numbers allowing selection
`set`	Sets and displays environment variable values and shell attributes
`shift`	Rotates positional parameters down one position
`shopt`	Toggles the values of variables controlling optional shell behavior
`source`	Reads and executes commands from a designated file in the current shell
`suspend`	Suspends the execution of the shell until a SIGCONT signal is received
`test`	Returns an exit status of 0 or 1 based on the specified condition
`time`	Displays the accumulated real, user, and system times executing command(s)
`times`	Displays the accumulated user and system shell times
`trap`	Executes the specified command if the specified system signal is received
`true`	Sets a result to successful status
`type`	Displays how the specified word would be interpreted if used as a command
`typeset`	Declares a variable or variable type
`ulimit`	Sets a limit on the specified resource for system users
`umask`	Sets default permissions for newly created files and directories
`unalias`	Removes the specified alias
`unset`	Removes the specified environment variable or shell attribute
`until`	Executes set commands until condition statement returns true
`wait`	Waits for the specified process to complete, and returns the exit status
`while`	Executes set commands while condition statement returns true
`{ c; }`	Group commands to execute within current shell