The following commands are builtin for bash or shell. This is not a complete list and emphasizes those that are more useful for shell programming.

: [arguments]

No effect; the command does nothing beyond expanding arguments and performing any specified redirections. A zero exit code is returned.

Execute the filename with the given arguments,

. sprog
source sprog *.gif

Exit from within a for, while, or until loop. If n is specified, break n levels. n must be >= 1.

break
break 2

Resume the next iteration of the enclosing for, while, or until loop. If n is specified, resume at the nth enclosing loop.

continue
continue 2

Declare variables and/or give them attributes. If no names are given, then display the values of variables instead. The options can be used to restrict output to variables with the specified attribute.
-f Use function names only
-r Make names readonly. These names cannot then be assigned values by subsequent assignment statements.
-x Mark names for export to subsequent commands via the environment.
-i The variable is treated as an integer; arithmetic evaluation is performed when the variable is assigned a value.


declare name=john_jacob_jingleheimer_schmidt
declare -i x=0 y=1
declare -r PI=3.1416

Output the args, separated by spaces. The return status is always 0. If -n is specified, the trailing newline is suppressed. If the -e option is given, interpretation of the following backslash-escaped characters is enabled. The -E option disables the interpretation of these escape characters, even on systems where they are interpreted by default.
\a alert (bell)
\b backspace
\c suppress trailing newline
\f form feed
\n new line
\r carriage return
\t horizontal tab
\v vertical tab
\\ backslash
\nnn the character whose ASCII code is nnn


echo "The value of name is", $NAME
echo -e "\tThis is a u with a circumflex \227 \a\a"

eval [arg ...]

The args are read and concatenated together into a single command. This command is then read and executed by the shell, and its exit status is returned as the value of the eval command. If there are no args, or only null arguments, eval returns true.

eval $CMD $ARG1 nowhere $ARG2

exec [[-] command [arguments]]

If command is specified, it replaces the shell. No new process is created. The arguments become the arguments to command.

exec ls /usr/tables $3

exit [n]

Cause the shell to exit with a status of n. If n is omitted, the exit status is that of the last command executed.

exit 0

export [-nf] [name[=word]] ...
export -p

The supplied names are marked for automatic export to the environment of subsequently executed commands. If the -f option is given, the names refer to functions. If no names are given, or if the -p option is supplied, a list of all names that are exported in this shell is printed. The -n option causes the export property to be removed from the named variables. An argument of -- disables option checking for the rest of the arguments. export returns an exit status of 0 unless an illegal option is encountered, one of the names is not a legal shell variable name, or -f is supplied with a name that is not a function.

export DISPLAY PATH
export -n TEMPNAME

getopts optstring name [args]

getopts is used by shell procedures to parse positional parameters. optstring contains the option letters to be recognized; If a letter is followed by a colon, the option is expected to have an argument, which should be separated from it by white space. Each time it is invoked, getopts places the next option in the shell variable name, initializing name if it does not exist, and the index of the next argument to be processed into the variable OPTIND. OPTIND is initialized to 1 each time the shell or a shell script is invoked. When an option requires an argument, getopts places that argument into the variable OPTARG. The shell does not reset OPTIND automatically; it must be manually reset between multiple calls to getopts within the same shell invocation if a new set of parameters is to be used.

If you executed the following command in a script that was called with the syntax: script3

   while  getopts  "xy:z"  o;  do -y 13 -z
        case  $o  in

        x  )   echo  "-x is there"  ;;
        y  )   echo  "-y  is there with arg $OPTARG"  ;;
        z  )   echo  "-z is there"  ;;
        ?)     echo "Usagei: script3 [-x] [-y arg] [-z] ;;
        esac
    done
   

would output:

   -y is there with arg 13
   -z is there
   

let arg [arg ...]

Each arg is an arithmetic expression to be evaluated If the last arg evaluates to 0, let returns 1; 0 is returned otherwise.

let x=$z+5
let a=3 b=4 c=2

local [name[=value] ...]

For each argument, create a local variable named name, and assign it value. When local is used within a function, it causes the variable name to have a visible scope restricted to that function

local NAME COUNT=0

read [-r] [name ...]

One line is read from the standard input, and the first word is assigned to the first name, the second word to the second name, and so on, with leftover words assigned to the last name. Only the characters in IFS are recognized as word delimiters. If no names are supplied, the line read is assigned to the variable REPLY. The return code is zero, unless end-of-file is encountered. There are several options:
• -r do not ignore a backslash-newline pair.
• -e use readline for input
• -s do not echo
• -t to   -   timeout after to seconds
• -a name   -   assign values to array name
• -p prompt   -   prompt user with string prompt

read -p "Enter your name" NAME
read -p "Enter your password: -s PASSWORD
read -p "Enter the dimensions" -a DIM

readonly [-f] [name ...]
readonly -p

The given names are marked readonly and the values of these names may not be changed by subsequent assignment. If the -f option is supplied, the functions corresponding to the names are so marked. If no arguments are given, or if the -p option is supplied, a list of all readonly names is printed. The return status is 0 unless an illegal option is encountered.

readonly NAME PASSWORD
readonly -f GetName

return [n]

Causes a function to exit with the return value specified by n. If n is omitted, the return status is that of the last command executed in the function body. If used outside a function, but during execution of a script by the . (source) command, it causes the shell to stop executing that script

return -1

set [--abefhkmnptuvxldCHP] [-o option] [arg ...]

set is the most complicated built-in function. Its purpose is to set the properties of the shell, and since there are lots of properties, set has lots of options. If no options are given, it displays the names and values of the shell variables Otherwise it sets the desired shell properties. A small subset of the options is:
-a Automatically mark variables which are mod­ ified or created for export to the environment of subsequent commands.
-b Cause the status of terminated background jobs to be reported immediately, rather than before the next primary prompt.
-e Exit immediately if a simple-command exits with a non-zero status. The shell does not exit if the command that fails is part of an until or while loop, part of an if statement, part of a && or || list, or if the command's return value is being inverted via !.
-f Disable pathname expansion.
-h Locate and remember function commands as functions are defined. Function commands are normally looked up when the function is executed.
-k All keyword arguments are placed in the environment for a command, not just those that precede the command name.
-m Monitor mode. Job control is enabled. This flag is on by default for interactive shells on systems that support it (see JOB CONTROL above). Background processes run in a separate process group and a line con­ taining their exit status is printed upon their completion.
-n Read commands but do not execute them. This may be used to check a shell script for syntax errors. This is ignored for interactive shells.
-o option-name The option-name can be one of the follow­ ing:

allexport
Same as -a.
braceexpand


set
set -f -b

shift [n]

The positional parameters from n+1 ... are renamed to $1 .... Parameters represented by the numbers $# down to $#-n+1 are unset. If n is 0, no parameters are changed. If n is not given, it is assumed to be 1. n must be a non-negative number less than or equal to $#. If n is greater than $#, the positional parameters are not changed. The return status is greater than 0 if n is greater than $# or less than 0; otherwise 0.

shift 5

test expr
[ expr ]

Return a status of 0 (true) or 1 (false) depending on the evaluation of the conditional expression expr. Expressions may be unary or binary. Unary expressions are often used to examine the status of a file. There are string operators and numeric comparison operators as well. Each operator and operand must be a separate argument. If file is of the form /dev/fd/n, then file descriptor n is checked.

-b file True if file exists and is block special.
-c file True if file exists and is character special.
-d file True if file exists and is a directory.
-e file True if file exists.
-f file True if file exists and is a regular file.
-g file True if file exists and is set-group-id.
-k file True if file has its ``sticky'' bit set.
-L file True if file exists and is a symbolic link.
-p file True if file exists and is a named pipe.
-r file True if file exists and is readable.
-s file True if file exists and has a size greater than zero.
-S file True if file exists and is a socket.
-t fd True if fd is opened on a terminal.
-u file True if file exists and its set-user-id bit is set.
-w file True if file exists and is writable.
-x file True if file exists and is executable.
-O file True if file exists and is owned by the effective user id.
-G file True if file exists and is owned by the effective group id.
file1 -nt file2 True if file1 is newer (according to modifi­ cation date) than file2.
file1 -ot file2 True if file1 is older than file2.
file1 -ef file True if file1 and file2 have the same device and inode numbers.
-z string True if the length of string is zero.
-n string string True if the length of string is non-zero.
string1 = string2 True if the strings are equal.
string1 != string2 True if the strings are not equal.
! expr True if expr is false.
expr1 -a expr2 True if both expr1 AND expr2 are true.
expr1 -o expr2 True if either expr1 OR expr2 is true.
arg1 OP arg2 OP is one of -eq, -ne, -lt, -le, -gt, or -ge


These arithmetic binary operators return true if arg1 is equal, not-equal, less-than, less-than-or-equal, greater-than, or greater-than-or-equal than arg2, respectively. Arg1 and arg2 may be positive integers, negative integers, or the special expression -l string, which evaluates to the length of string.

test -e /etc/nologin
test $NAME="Dilbert"

unset [-fv] [name ...]

For each name, remove the corresponding variable or, given the -f option, function. An argument of -- disables option checking for the rest of the arguments. Note that PATH, IFS, PPID, PS1, PS2, UID, and EUID cannot be unset. If any of RANDOM, SECONDS, LINENO, or HISTCMD are unset, they lose their special properties, even if they are subse­

unset PATH
unset NAME COUNT
unset -f ValueCheck

wait [n]

Termination status. n may be a process ID or a job specification; if a job spec is given, all processes in that job's pipeline are waited for. If n is not given, all currently active child processes are waited for, and the return status is zero. If n specifies a non-existant process or job, the return status is 127. Otherwise, the return status is the exit status of the last process or job waited for.

wait 3154