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.1‐2008, 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         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

       Zero.

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.1‐2008 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(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.1‐2008, Section 12.2, Utility
       Syntax Guidelines

COPYRIGHT         top

       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 .
IEEE/The Open Group                 2013                        READONLY(1P)