NAME

readonly - set the readonly attribute for variables

SYNOPSIS

readonly name[=word]...

readonly -p


DESCRIPTION

The variables whose names are specified shall be given the readonly attribute. The values of variables with the readonly attribute cannot be changed by subsequent assignment, nor can those variables be unset by the unset utility.

The readonly special built-in shall support the Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.

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 shall format 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 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 reinput to the shell.

When no arguments are given, the results are unspecified.

OPTIONS

None.

OPERANDS

None.

STDIN

None.

INPUT FILES

None.

ENVIRONMENT VARIABLES

None.

ASYNCHRONOUS EVENTS

None.

STDOUT

None.

STDERR

None.

OUTPUT FILES

None.

EXTENDED DESCRIPTION

None.

EXIT STATUS

Zero.

CONSEQUENCES OF ERRORS

None.

APPLICATION USAGE

None.

EXAMPLES

readonly HOME PWD

RATIONALE

Some historical shells preserve the readonly attribute across separate invocations. This volume of IEEE Std 1003.1-2001 allows this behavior, but does not require it.

The -p option allows portable access to the values that can be saved and then later restored using, for example, a dot script. Also see the RATIONALE for export for a description of the no-argument and -p output cases and a related example.

Read-only functions were considered, but they were omitted as not being historical practice or particularly useful. Furthermore, functions must not be read-only across invocations to preclude ``spoofing'' (spoofing is the term for the practice of creating a program that acts like a well-known utility with the intent of subverting the real intent of the user) of administrative or security-relevant (or security-conscious) shell scripts.

FUTURE DIRECTIONS

None.

SEE ALSO

Special Built-In Utilities

CHANGE HISTORY

Issue 6

IEEE PASC Interpretation 1003.2 #203 is applied, clarifying the format when a variable is unset.