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NAME


readonly - shell built-in function to protect the value of the given
variable from reassignment

SYNOPSIS


sh
readonly [name]...


ksh
**readonly [name [= value]]...


**readonly -p


ksh93
++readonly [-p] [name [= value]]...


DESCRIPTION


sh
The given names are marked readonly and the values of these names may not
be changed by subsequent assignment. If no arguments are given, a list of
all readonly names is printed.

ksh
The given names are marked readonly and these names cannot be changed by
subsequent assignment.


When -p is specified, readonly writes to the standard output the names
and values of all read-only variables, in the following format:

"readonly %s=%s\n", name, value


if name is set, and:

"readonly $s\n", name


if name is unset.


The shell formats the output, including the proper use of quoting, so
that it is suitable for reinput to the shell as commands that achieve the
same value and readonly attribute-setting results in a shell execution
environment in which:

1. Variables with values set at the time they were output do not
have the readonly attribute set.

2. Variables that were unset at the time they were output do not
have a value at the time at which the saved output is re-input
to the shell.


On this manual page, ksh(1) commands that are preceded by one or two **
(asterisks) are treated specially in the following ways:

1. Variable assignment lists preceding the command remain in
effect when the command completes.

2. I/O redirections are processed after variable assignments.

3. Errors cause a script that contains them to abort.

4. Words, following a command preceded by ** that are in the
format of a variable assignment, are expanded with the same
rules as a variable assignment. This means that tilde
substitution is performed after the = sign and word splitting
and file name generation are not performed.

ksh93
readonly sets the readonly attribute on each of the variables specified
by name which prevents their values from being changed. If =value is
specified, the variable name is set to value before the variable is made
readonly.


If no names are specified then the names and values of all readonly
variables are written to standard output.


readonly is built-in to the shell as a declaration command so that field
splitting and pathname expansion are not performed on the arguments.
Tilde expansion occurs on value.

-p
Causes the output to be in a form of readonly commands that can be
used as input to the shell to recreate the current set of readonly
variables.


On this manual page, ksh93(1) commands that are preceded by one or two +
symbols are treated specially in the following ways:

1. Variable assignment lists preceding the command remain in
effect when the command completes.

2. I/O redirections are processed after variable assignments.

3. Errors cause a script that contains them to abort.

4. They are not valid function names.

5. Words, following a command preceded by ++ that are in the
format of a variable assignment, are expanded with the same
rules as a variable assignment. This means that tilde
substitution is performed after the = sign and field splitting
and file name generation are not performed.

EXIT STATUS


ksh93
The following exit values are returned:

0
Successful completion.


>0
An error occurred.


SEE ALSO


ksh(1), ksh93(1), sh(1), typeset(1), attributes(7)


April 9, 2016 READONLY(1)