READONLY(1) User Commands READONLY(1)

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)