248 lines
8.1 KiB
HTML
248 lines
8.1 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<meta name="generator" content="HTML Tidy, see www.w3.org">
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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>mesg</title>
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</head>
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<body bgcolor="white">
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<script type="text/javascript" language="JavaScript" src="../jscript/codes.js">
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<basefont size="3"> <a name="mesg"></a> <a name="tag_04_86"></a><!-- mesg -->
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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_86_01"></a>NAME</h4>
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<blockquote>mesg - permit or deny messages</blockquote>
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<h4><a name="tag_04_86_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<div class="box"><code><tt><sup>[<a href="javascript:open_code('UP')">UP</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> mesg</tt> <b>[</b><tt>y|n</tt><b>]</b><tt><img src="../images/opt-end.gif" alt="[Option End]" border=
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"0"></tt></code></div>
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</blockquote>
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<h4><a name="tag_04_86_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>mesg</i> utility shall control whether other users are allowed to send messages via <a href=
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"../utilities/write.html"><i>write</i></a>, <a href="../utilities/talk.html"><i>talk</i></a>, or other utilities to a terminal
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device. The terminal device affected shall be determined by searching for the first terminal in the sequence of devices associated
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with standard input, standard output, and standard error, respectively. With no arguments, <i>mesg</i> shall report the current
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state without changing it. Processes with appropriate privileges may be able to send messages to the terminal independent of the
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current state.</p>
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</blockquote>
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<h4><a name="tag_04_86_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_86_05"></a>OPERANDS</h4>
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<blockquote>
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<p>The following operands shall be supported in the POSIX locale:</p>
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<dl compact>
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<dt><i>y</i></dt>
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<dd>Grant permission to other users to send messages to the terminal device.</dd>
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<dt><i>n</i></dt>
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<dd>Deny permission to other users to send messages to the terminal device.</dd>
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</dl>
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</blockquote>
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<h4><a name="tag_04_86_06"></a>STDIN</h4>
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<blockquote>
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<p>Not used.</p>
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</blockquote>
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<h4><a name="tag_04_86_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_86_08"></a>ENVIRONMENT VARIABLES</h4>
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<blockquote>
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<p>The following environment variables shall affect the execution of <i>mesg</i>:</p>
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<dl compact>
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<dt><i>LANG</i></dt>
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<dd>Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of
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IEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap08.html#tag_08_02">Section 8.2, Internationalization Variables</a> for
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the precedence of internationalization variables used to determine the values of locale categories.)</dd>
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<dt><i>LC_ALL</i></dt>
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<dd>If set to a non-empty string value, override the values of all the other internationalization variables.</dd>
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<dt><i>LC_CTYPE</i></dt>
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<dd>Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as
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opposed to multi-byte characters in arguments).</dd>
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<dt><i>LC_MESSAGES</i></dt>
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<dd>Determine the locale that should be used to affect the format and contents of diagnostic messages written (by <i>mesg</i>) to
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standard error.</dd>
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<dt><i>NLSPATH</i></dt>
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<dd><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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Determine the location of message catalogs for the processing of <i>LC_MESSAGES .</i> <img src="../images/opt-end.gif" alt=
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"[Option End]" border="0"></dd>
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</dl>
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</blockquote>
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<h4><a name="tag_04_86_09"></a>ASYNCHRONOUS EVENTS</h4>
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<blockquote>
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<p>Default.</p>
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</blockquote>
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<h4><a name="tag_04_86_10"></a>STDOUT</h4>
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<blockquote>
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<p>If no operand is specified, <i>mesg</i> shall display the current terminal state in an unspecified format.</p>
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</blockquote>
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<h4><a name="tag_04_86_11"></a>STDERR</h4>
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<blockquote>
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<p>The standard error shall be used only for diagnostic messages.</p>
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</blockquote>
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<h4><a name="tag_04_86_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_86_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_86_14"></a>EXIT STATUS</h4>
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<blockquote>
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<p>The following exit values shall be returned:</p>
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<dl compact>
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<dt> 0</dt>
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<dd>Receiving messages is allowed.</dd>
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<dt> 1</dt>
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<dd>Receiving messages is not allowed.</dd>
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<dt>>1</dt>
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<dd>An error occurred.</dd>
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</dl>
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</blockquote>
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<h4><a name="tag_04_86_15"></a>CONSEQUENCES OF ERRORS</h4>
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<blockquote>
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<p>Default.</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_86_16"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>The mechanism by which the message status of the terminal is changed is unspecified. Therefore, unspecified actions may cause
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the status of the terminal to change after <i>mesg</i> has successfully completed. These actions may include, but are not limited
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to: another invocation of the <i>mesg</i> utility, login procedures; invocation of the <a href=
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"../utilities/stty.html"><i>stty</i></a> utility, invocation of the <a href="../utilities/chmod.html"><i>chmod</i></a> utility or
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<a href="../functions/chmod.html"><i>chmod</i>()</a> function, and so on.</p>
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</blockquote>
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<h4><a name="tag_04_86_17"></a>EXAMPLES</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_86_18"></a>RATIONALE</h4>
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<blockquote>
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<p>The terminal changed by <i>mesg</i> is that associated with the standard input, output, or error, rather than the controlling
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terminal for the session. This is because users logged in more than once should be able to change any of their login terminals
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without having to stop the job running in those sessions. This is not a security problem involving the terminals of other users
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because appropriate privileges would be required to affect the terminal of another user.</p>
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<p>The method of checking each of the first three file descriptors in sequence until a terminal is found was adopted from System
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V.</p>
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<p>The file <b>/dev/tty</b> is not specified for the terminal device because it was thought to be too restrictive. Typical
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environment changes for the <i>n</i> operand are that write permissions are removed for <i>others</i> and <i>group</i> from the
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appropriate device. It was decided to leave the actual description of what is done as unspecified because of potential differences
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between implementations.</p>
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<p>The format for standard output is unspecified because of differences between historical implementations. This output is
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generally not useful to shell scripts (they can use the exit status), so exact parsing of the output is unnecessary.</p>
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</blockquote>
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<h4><a name="tag_04_86_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_86_20"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="talk.html"><i>talk</i></a> , <a href="write.html"><i>write</i>()</a></p>
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</blockquote>
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<h4><a name="tag_04_86_21"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 2.</p>
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</blockquote>
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<h4><a name="tag_04_86_22"></a>Issue 6</h4>
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<blockquote>
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<p>This utility is marked as part of the User Portability Utilities option.</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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<hr size="2" noshade>
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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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]</font></center>
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