xenial (1) readonly.1posix.gz

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


       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 .

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