219 lines
6.1 KiB
HTML
219 lines
6.1 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<meta name="generator" content="HTML Tidy, see www.w3.org">
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 -->
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<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
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<title>readonly</title>
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<body bgcolor="white">
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<basefont size="3"> <a name="readonly"></a> <a name="tag_04_118"></a><!-- readonly -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_04_118_01"></a>NAME</h4>
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<blockquote>readonly - set the readonly attribute for variables</blockquote>
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<h4><a name="tag_04_118_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<p><code><tt>readonly name</tt><b>[</b><tt>=</tt><i>word</i><b>]</b><tt>...<br>
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<br>
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readonly -p<br>
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</tt></code></p>
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</blockquote>
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<h4><a name="tag_04_118_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The variables whose <i>name</i>s are specified shall be given the <i>readonly</i> attribute. The values of variables with the
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<i>readonly</i> attribute cannot be changed by subsequent assignment, nor can those variables be unset by the <a href=
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"../utilities/unset.html"><i>unset</i></a> utility.</p>
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<p>The <i>readonly</i> special built-in shall support the Base Definitions volume of IEEE Std 1003.1-2001, <a href=
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"../basedefs/xbd_chap12.html#tag_12_02">Section 12.2, Utility Syntax Guidelines</a>.</p>
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<p>When <b>-p</b> is specified, <i>readonly</i> writes to the standard output the names and values of all read-only variables, in
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the following format:</p>
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<pre>
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<tt>"readonly %s=%s\n", <</tt><i>name</i><tt>>, <</tt><i>value</i><tt>>
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</tt>
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</pre>
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<p>if <i>name</i> is set, and</p>
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<pre>
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<tt>"readonly %s\n", <</tt><i>name</i><tt>>
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</tt>
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</pre>
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<p>if <i>name</i> is unset.</p>
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<p>The shell shall format the output, including the proper use of quoting, so that it is suitable for reinput to the shell as
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commands that achieve the same value and <i>readonly</i> attribute-setting results in a shell execution environment in which:</p>
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<ol>
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<li>
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<p>Variables with values at the time they were output do not have the <i>readonly</i> attribute set.</p>
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</li>
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<li>
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<p>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
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the shell.</p>
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</li>
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</ol>
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<p>When no arguments are given, the results are unspecified.</p>
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</blockquote>
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<h4><a name="tag_04_118_04"></a>OPTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_118_05"></a>OPERANDS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_118_06"></a>STDIN</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_118_07"></a>INPUT FILES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_118_08"></a>ENVIRONMENT VARIABLES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_118_09"></a>ASYNCHRONOUS EVENTS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_118_10"></a>STDOUT</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_118_11"></a>STDERR</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_118_12"></a>OUTPUT FILES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_118_13"></a>EXTENDED DESCRIPTION</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_118_14"></a>EXIT STATUS</h4>
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<blockquote>
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<p>Zero.</p>
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</blockquote>
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<h4><a name="tag_04_118_15"></a>CONSEQUENCES OF ERRORS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_04_118_16"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_118_17"></a>EXAMPLES</h4>
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<blockquote>
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<pre>
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<tt>readonly HOME PWD
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</tt>
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</pre>
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</blockquote>
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<h4><a name="tag_04_118_18"></a>RATIONALE</h4>
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<blockquote>
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<p>Some historical shells preserve the <i>readonly</i> attribute across separate invocations. This volume of
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IEEE Std 1003.1-2001 allows this behavior, but does not require it.</p>
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<p>The <b>-p</b> option allows portable access to the values that can be saved and then later restored using, for example, a <a
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href="../utilities/dot.html"><i>dot</i></a> script. Also see the RATIONALE for <a href="export.html#tag_04_49"><i>export</i></a>
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for a description of the no-argument and <b>-p</b> output cases and a related example.</p>
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<p>Read-only functions were considered, but they were omitted as not being historical practice or particularly useful. Furthermore,
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functions must not be read-only across invocations to preclude ``spoofing'' (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 the real intent of the user) of administrative or
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security-relevant (or security-conscious) shell scripts.</p>
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</blockquote>
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<h4><a name="tag_04_118_19"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_118_20"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="xcu_chap02.html#tag_02_14"><i>Special Built-In Utilities</i></a></p>
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</blockquote>
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<h4><a name="tag_04_118_21"></a>CHANGE HISTORY</h4>
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<h4><a name="tag_04_118_22"></a>Issue 6</h4>
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<blockquote>
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<p>IEEE PASC Interpretation 1003.2 #203 is applied, clarifying the format when a variable is unset.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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<hr>
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<center><font size="2"><!--footer start-->
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UNIX ® is a registered Trademark of The Open Group.<br>
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POSIX ® is a registered Trademark of The IEEE.<br>
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[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href=
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"../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>
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