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READONLY
Section: POSIX Programmer's Manual (1P)
Updated: 2003
Index
Return to Main Contents
PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
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 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
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 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
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- OPTIONS
-
- OPERANDS
-
- STDIN
-
- INPUT FILES
-
- ENVIRONMENT VARIABLES
-
- ASYNCHRONOUS EVENTS
-
- STDOUT
-
- STDERR
-
- OUTPUT FILES
-
- EXTENDED DESCRIPTION
-
- EXIT STATUS
-
- CONSEQUENCES OF ERRORS
-
- APPLICATION USAGE
-
- EXAMPLES
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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