mirror of https://github.com/mkerrisk/man-pages
152 lines
3.9 KiB
Groff
152 lines
3.9 KiB
Groff
.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.TH "READONLY" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.\" readonly
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.SH NAME
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readonly \- set the readonly attribute for variables
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.SH SYNOPSIS
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.LP
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\fBreadonly name\fP\fB[\fP\fB=\fP\fIword\fP\fB]\fP\fB...
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.br
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.sp
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readonly -p
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.br
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\fP
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.SH DESCRIPTION
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.LP
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The variables whose \fIname\fPs are specified shall be given the \fIreadonly\fP
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attribute. The values of variables with the
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\fIreadonly\fP attribute cannot be changed by subsequent assignment,
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nor can those variables be unset by the \fIunset\fP utility. If the
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name of a variable is followed by = \fIword\fP, then the value of
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that
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variable shall be set to \fIword\fP.
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.LP
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The \fIreadonly\fP special built-in shall support the Base Definitions
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volume of IEEE\ Std\ 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
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.LP
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When \fB-p\fP is specified, \fIreadonly\fP writes to the standard
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output the names and values of all read-only variables, in
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the following format:
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.sp
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.RS
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.nf
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\fB"readonly %s=%s\\n", <\fP\fIname\fP\fB>, <\fP\fIvalue\fP\fB>
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\fP
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.fi
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.RE
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.LP
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if \fIname\fP is set, and
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.sp
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.RS
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.nf
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\fB"readonly %s\\n", <\fP\fIname\fP\fB>
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\fP
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.fi
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.RE
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.LP
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if \fIname\fP is unset.
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.LP
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The shell shall format the output, including the proper use of quoting,
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so that it is suitable for reinput to the shell as
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commands that achieve the same value and \fIreadonly\fP attribute-setting
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results in a shell execution environment in which:
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.IP " 1." 4
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Variables with values at the time they were output do not have the
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\fIreadonly\fP attribute set.
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.LP
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.IP " 2." 4
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Variables that were unset at the time they were output do not have
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a value at the time at which the saved output is reinput to
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the shell.
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.LP
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.LP
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When no arguments are given, the results are unspecified.
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.SH OPTIONS
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.LP
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See the DESCRIPTION.
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.SH OPERANDS
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.LP
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See the DESCRIPTION.
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.SH STDIN
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.LP
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Not used.
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.SH INPUT FILES
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.LP
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None.
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.SH ENVIRONMENT VARIABLES
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.LP
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None.
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.SH ASYNCHRONOUS EVENTS
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.LP
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Default.
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.SH STDOUT
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.LP
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See the DESCRIPTION.
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.SH STDERR
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.LP
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The standard error shall be used only for diagnostic messages.
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.SH OUTPUT FILES
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.LP
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None.
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.SH EXTENDED DESCRIPTION
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.LP
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None.
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.SH EXIT STATUS
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.LP
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Zero.
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.SH CONSEQUENCES OF ERRORS
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.LP
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Default.
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.LP
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\fIThe following sections are informative.\fP
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.SH APPLICATION USAGE
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.LP
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None.
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.SH EXAMPLES
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.sp
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.RS
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.nf
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\fBreadonly HOME PWD
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\fP
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.fi
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.RE
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.SH RATIONALE
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.LP
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Some historical shells preserve the \fIreadonly\fP attribute across
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separate invocations. This volume of
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IEEE\ Std\ 1003.1-2001 allows this behavior, but does not require
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it.
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.LP
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The \fB-p\fP option allows portable access to the values that can
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be saved and then later restored using, for example, a \fIdot\fP script.
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Also see the RATIONALE for \fIexport\fP
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for a description of the no-argument and \fB-p\fP output cases and
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a related example.
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.LP
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Read-only functions were considered, but they were omitted as not
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being historical practice or particularly useful. Furthermore,
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functions must not be read-only across invocations to preclude ``spoofing''
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(spoofing is the term for the practice of creating a
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program that acts like a well-known utility with the intent of subverting
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the real intent of the user) of administrative or
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security-relevant (or security-conscious) shell scripts.
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.SH FUTURE DIRECTIONS
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.LP
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None.
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.SH SEE ALSO
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.LP
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\fISpecial Built-In Utilities\fP
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document. The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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