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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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READONLY(1P) POSIX Programmer's Manual READONLY(1P)
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.
readonly — set the readonly attribute for variables
readonly name[=word]...
readonly -p
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.1‐2017, 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.
See the DESCRIPTION.
See the DESCRIPTION.
Not used.
None.
None.
Default.
See the DESCRIPTION.
The standard error shall be used only for diagnostic messages.
None.
None.
0 All name operands were successfully marked readonly.
>0 At least one name could not be marked readonly, or the -p
option was specified and an error occurred.
Default.
The following sections are informative.
None.
readonly HOME PWD
Some historical shells preserve the readonly attribute across
separate invocations. This volume of POSIX.1‐2017 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(1p) 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.
None.
Section 2.14, Special Built-In Utilities
The Base Definitions volume of POSIX.1‐2017, Section 12.2,
Utility Syntax Guidelines
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 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 .
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 .
IEEE/The Open Group 2017 READONLY(1P)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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