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Linux 2.6 - man page for readonly (linux section 1posix)

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

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 prac-
       tice or particularly useful. Furthermore, functions must not be read-only  across  invoca-
       tions  to  preclude ``spoofing'' (spoofing is the term for the practice of creating a pro-
       gram 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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003				      READONLY(P)


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