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518.

Set variable values and attributes.

Declare variables and give them attributes. If no NAMEs are given,
display the attributes and values of all variables.

Options:
-f[tab]restrict action or display to function names and definitions
-F[tab]restrict display to function names only (plus line number and
[tab][tab]source file when debugging)
-g[tab]create global variables when used in a shell function; otherwise
[tab][tab]ignored
-p[tab]display the attributes and value of each NAME

Options which set attributes:
-a[tab]to make NAMEs indexed arrays (if supported)
-A[tab]to make NAMEs associative arrays (if supported)
-i[tab]to make NAMEs have the `integer' attribute
-l[tab]to convert NAMEs to lower case on assignment
-n[tab]make NAME a reference to the variable named by its value
-r[tab]to make NAMEs readonly
-t[tab]to make NAMEs have the `trace' attribute
-u[tab]to convert NAMEs to upper case on assignment
-x[tab]to make NAMEs export

Using `+' instead of `-' turns off the given attribute.

Variables with the integer attribute have arithmetic evaluation (see
the `let' command) performed when the variable is assigned a value.

When used in a function, `declare' makes NAMEs local, as with the `local'
command. The `-g' option suppresses this behavior.

Exit Status:
Returns success unless an invalid option is supplied or a variable
assignment error occurs.

519.

Set variable values and attributes.

A synonym for `declare'. See `help declare'.

520.

Define local variables.

Create a local variable called NAME, and give it VALUE. OPTION can
be any option accepted by `declare'.

Local variables can only be used within a function; they are visible
only to the function where they are defined and its children.

Exit Status:
Returns success unless an invalid option is supplied, a variable
assignment error occurs, or the shell is not executing a function.

521.

Write arguments to the standard output.

Display the ARGs, separated by a single space character and followed by a
newline, on the standard output.

Options:
-n[tab]do not append a newline
-e[tab]enable interpretation of the following backslash escapes
-E[tab]explicitly suppress interpretation of backslash escapes

`echo' interprets the following backslash-escaped characters:
\a[tab]alert (bell)
\b[tab]backspace
\c[tab]suppress further output
\e[tab]escape character
\E[tab]escape character
\f[tab]form feed
\n[tab]new line
\r[tab]carriage return
\t[tab]horizontal tab
\v[tab]vertical tab
\\[tab]backslash
\0nnn[tab]the character whose ASCII code is NNN (octal). NNN can be
[tab][tab]0 to 3 octal digits
\xHH[tab]the eight-bit character whose value is HH (hexadecimal). HH
[tab][tab]can be one or two hex digits

Exit Status:
Returns success unless a write error occurs.

522.

Write arguments to the standard output.

Display the ARGs on the standard output followed by a newline.

Options:
-n[tab]do not append a newline

Exit Status:
Returns success unless a write error occurs.

523.

Enable and disable shell builtins.

Enables and disables builtin shell commands. Disabling allows you to
execute a disk command which has the same name as a shell builtin
without using a full pathname.

Options:
-a[tab]print a list of builtins showing whether or not each is enabled
-n[tab]disable each NAME or display a list of disabled builtins
-p[tab]print the list of builtins in a reusable format
-s[tab]print only the names of Posix `special' builtins

Options controlling dynamic loading:
-f[tab]Load builtin NAME from shared object FILENAME
-d[tab]Remove a builtin loaded with -f

Without options, each NAME is enabled.

To use the `test' found in $PATH instead of the shell builtin
version, type `enable -n test'.

Exit Status:
Returns success unless NAME is not a shell builtin or an error occurs.

524.

Execute arguments as a shell command.

Combine ARGs into a single string, use the result as input to the shell,
and execute the resulting commands.

Exit Status:
Returns exit status of command or success if command is null.

525.

Parse option arguments.

Getopts is used by shell procedures to parse positional parameters
as options.

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 will place 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 shell
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 shell variable OPTARG.

getopts reports errors in one of two ways. If the first character
of OPTSTRING is a colon, getopts uses silent error reporting. In
this mode, no error messages are printed. If an invalid option is
seen, getopts places the option character found into OPTARG. If a
required argument is not found, getopts places a ':' into NAME and
sets OPTARG to the option character found. If getopts is not in
silent mode, and an invalid option is seen, getopts places '?' into
NAME and unsets OPTARG. If a required argument is not found, a '?'
is placed in NAME, OPTARG is unset, and a diagnostic message is
printed.

If the shell variable OPTERR has the value 0, getopts disables the
printing of error messages, even if the first character of
OPTSTRING is not a colon. OPTERR has the value 1 by default.

Getopts normally parses the positional parameters ($0 - $9), but if
more arguments are given, they are parsed instead.

Exit Status:
Returns success if an option is found; fails if the end of options is
encountered or an error occurs.

526.

Replace the shell with the given command.

Execute COMMAND, replacing this shell with the specified program.
ARGUMENTS become the arguments to COMMAND. If COMMAND is not specified,
any redirections take effect in the current shell.

Options:
-a name[tab]pass NAME as the zeroth argument to COMMAND
-c[tab]execute COMMAND with an empty environment
-l[tab]place a dash in the zeroth argument to COMMAND

If the command cannot be executed, a non-interactive shell exits, unless
the shell option `execfail' is set.

Exit Status:
Returns success unless COMMAND is not found or a redirection error occurs.

527.

Exit the shell.

Exits the shell with a status of N. If N is omitted, the exit status
is that of the last command executed.