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 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

       Special Built-In Utilities

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2003 Edition, Standard for Information Technology  --  Portable  Operating  System
       Interface  (POSIX), The Open Group Base Specifications 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
       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 .