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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 dif-
       fer (consult the corresponding Linux manual page for details of Linux behavior), or the interface  may  not  be
       implemented on Linux.

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 IEEE Std 1003.1-2001, 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.

EXAMPLES
              readonly HOME PWD

RATIONALE
       Some   historical  shells  preserve  the  readonly  attribute  across  separate  invocations.  This  volume  of
       IEEE Std 1003.1-2001 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  exam-
       ple,  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 subvert-
       ing  the real intent of the user) of administrative or security-relevant (or security-conscious) shell scripts.

FUTURE DIRECTIONS
       None.

SEE ALSO
       Special Built-In Utilities

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Stan-
       dard  for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica-
       tions Issue 6, Copyright (C) 2001-2003 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 Stan-
       dard, 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 .



IEEE/The Open Group                  2003                         READONLY(1P)