The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.

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

CHANGE HISTORY

Issue 6

IEEE PASC Interpretation 1003.2 #203 is applied, clarifying the format when a variable is unset.

IEEE Std 1003.1-2001/Cor 1-2002, item XCU/TC1/D6/5 is applied so that the reference page sections use terms as described in the Utility Description Defaults ( Utility Description Defaults ). No change in behavior is intended.

IEEE Std 1003.1-2001/Cor 1-2002, item XCU/TC1/D6/7 is applied, adding the following text to the end of the first paragraph of the DESCRIPTION: ``If the name of a variable is followed by = word, then the value of that variable shall be set to word.''. The reason for this change is that the SYNOPSIS for readonly includes:

readonly name[=word]...

but the meaning of the optional ``= word'' is never explained in the text.

End of informative text.

UNIX ® is a registered Trademark of The Open Group.
POSIX ® is a registered Trademark of The IEEE.
[ Main Index | XBD | XCU | XSH | XRAT ]