READONLY
Section: POSIX Programmer's Manual (1P)
Updated: 2013
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 POSIX.1-2008,
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 POSIX.1-2008 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
Section 2.14,
Special Built-In Utilities
The Base Definitions volume of POSIX.1-2008,
Section 12.2,
Utility Syntax Guidelines
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.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
-
|
|
- Running on 
-
:
: 