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



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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.1-2017, 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
       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
        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
       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.1-2017 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 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.1-2017, Section 12.2, Utility
       Syntax Guidelines

COPYRIGHT
       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(1)
