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 (consult the corresponding
Linux manual page for details of Linux behavior), or the interface may
not be implemented on Linux.
NAMEreadonly — set the readonly attribute for variables
SYNOPSISreadonly 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.
EXAMPLESreadonly 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 Syn‐
tax 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 Electri‐
cal 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.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 READONLY(1P)
