readonly(1p) — Linux manual page

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

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

PROLOG         top

       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         top

       readonly — set the readonly attribute for variables

SYNOPSIS         top

       readonly name[=word]...

       readonly -p

DESCRIPTION         top

       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.

OPTIONS         top

       See the DESCRIPTION.

OPERANDS         top

       See the DESCRIPTION.

STDIN         top

       Not used.

INPUT FILES         top

       None.

ENVIRONMENT VARIABLES         top

       None.

ASYNCHRONOUS EVENTS         top

       Default.

STDOUT         top

       See the DESCRIPTION.

STDERR         top

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES         top

       None.

EXTENDED DESCRIPTION         top

       None.

EXIT STATUS         top

        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.

CONSEQUENCES OF ERRORS         top

       Default.

       The following sections are informative.

APPLICATION USAGE         top

       None.

EXAMPLES         top

       readonly HOME PWD

RATIONALE         top

       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.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       Section 2.14, Special Built-In Utilities

       The Base Definitions volume of POSIX.1‐2017, Section 12.2,
       Utility Syntax Guidelines

COPYRIGHT         top

       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)