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READONLY(1P) POSIX Programmer's Manual READONLY(1P)

PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (con-
sult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on
Linux.

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. If the name
of a variable is followed by = word, then the value of that variable shall be set to word.

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 fol-
lowing 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
See the DESCRIPTION.

OPERANDS
See the DESCRIPTION.

STDIN
Not used.

INPUT FILES
None.

ENVIRONMENT VARIABLES
None.

ASYNCHRONOUS EVENTS
Default.

STDOUT
See the DESCRIPTION.

STDERR
The standard error shall be used only for diagnostic messages.

OUTPUT FILES
None.

EXTENDED DESCRIPTION
None.

EXIT STATUS
Zero.

CONSEQUENCES OF ERRORS
Default.

The following sections are informative.

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 exam-
ple.

Read-only functions were considered, but they were omitted as not being historical practice or particularly useful. Fur-
thermore, functions must not be read-only across invocations to preclude ``spoofing'' (spoofing is the term for the prac-
tice 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.