298 lines
11 KiB
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298 lines
11 KiB
HTML
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<title>env</title>
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<basefont size="3"> <a name="env"></a> <a name="tag_04_43"></a><!-- env -->
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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_43_01"></a>NAME</h4>
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<blockquote>env - set the environment for command invocation</blockquote>
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<h4><a name="tag_04_43_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<p><code><tt>env</tt> <b>[</b><tt>-i</tt><b>][</b><i>name</i><tt>=</tt><i>value</i><b>]</b><tt>...</tt> <b>[</b><i>utility</i>
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<b>[</b><i>argument</i><tt>...</tt><b>]]</b></code></p>
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</blockquote>
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<h4><a name="tag_04_43_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>env</i> utility shall obtain the current environment, modify it according to its arguments, then invoke the utility named
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by the <i>utility</i> operand with the modified environment.</p>
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<p>Optional arguments shall be passed to <i>utility</i>.</p>
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<p>If no <i>utility</i> operand is specified, the resulting environment shall be written to the standard output, with one
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<i>name</i>= <i>value</i> pair per line.</p>
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</blockquote>
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<h4><a name="tag_04_43_04"></a>OPTIONS</h4>
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<blockquote>
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<p>The <i>env</i> utility shall conform to 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>The following options shall be supported:</p>
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<dl compact>
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<dt><b>-i</b></dt>
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<dd>Invoke <i>utility</i> with exactly the environment specified by the arguments; the inherited environment shall be ignored
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completely.</dd>
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</dl>
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</blockquote>
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<h4><a name="tag_04_43_05"></a>OPERANDS</h4>
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<blockquote>
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<p>The following operands shall be supported:</p>
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<dl compact>
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<dt><i>name</i>=<i>value</i></dt>
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<dd>Arguments of the form <i>name</i>= <i>value</i> shall modify the execution environment, and shall be placed into the inherited
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environment before the <i>utility</i> is invoked.</dd>
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<dt><i>utility</i></dt>
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<dd>The name of the utility to be invoked. If the <i>utility</i> operand names any of the special built-in utilities in <a href=
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"xcu_chap02.html#tag_02_14"><i>Special Built-In Utilities</i></a> , the results are undefined.</dd>
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<dt><i>argument</i></dt>
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<dd>A string to pass as an argument for the invoked utility.</dd>
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</dl>
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</blockquote>
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<h4><a name="tag_04_43_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_43_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_43_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>env</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 to standard
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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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<dt><i>PATH</i></dt>
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<dd>Determine the location of the <i>utility</i>, as described in the Base Definitions volume of IEEE Std 1003.1-2001, <a
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href="../basedefs/xbd_chap08.html">Chapter 8, Environment Variables</a>. If <i>PATH</i> is specified as a <i>name</i>= <i>value</i>
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operand to <i>env</i>, the <i>value</i> given shall be used in the search for <i>utility</i>.</dd>
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</dl>
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</blockquote>
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<h4><a name="tag_04_43_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_43_10"></a>STDOUT</h4>
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<blockquote>
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<p>If no <i>utility</i> operand is specified, each <i>name</i>= <i>value</i> pair in the resulting environment shall be written in
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the form:</p>
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<pre>
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<tt>"%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 the <i>utility</i> operand is specified, the <i>env</i> utility shall not write to standard output.</p>
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</blockquote>
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<h4><a name="tag_04_43_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_43_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_43_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_43_14"></a>EXIT STATUS</h4>
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<blockquote>
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<p>If <i>utility</i> is invoked, the exit status of <i>env</i> shall be the exit status of <i>utility</i>; otherwise, the
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<i>env</i> utility shall exit with one of the following values:</p>
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<dl compact>
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<dt> 0</dt>
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<dd>The <i>env</i> utility completed successfully.</dd>
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<dt>1-125</dt>
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<dd>An error occurred in the <i>env</i> utility.</dd>
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<dt> 126</dt>
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<dd>The utility specified by <i>utility</i> was found but could not be invoked.</dd>
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<dt> 127</dt>
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<dd>The utility specified by <i>utility</i> could not be found.</dd>
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</dl>
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</blockquote>
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<h4><a name="tag_04_43_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_43_16"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>The <a href="../utilities/command.html"><i>command</i></a>, <i>env</i>, <a href="../utilities/nice.html"><i>nice</i></a>, <a
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href="../utilities/nohup.html"><i>nohup</i></a>, <a href="../utilities/time.html"><i>time</i></a>, and <a href=
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"../utilities/xargs.html"><i>xargs</i></a> utilities have been specified to use exit code 127 if an error occurs so that
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applications can distinguish "failure to find a utility" from "invoked utility exited with an error indication". The value 127
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was chosen because it is not commonly used for other meanings; most utilities use small values for "normal error conditions" and
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the values above 128 can be confused with termination due to receipt of a signal. The value 126 was chosen in a similar manner to
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indicate that the utility could be found, but not invoked. Some scripts produce meaningful error messages differentiating the 126
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and 127 cases. The distinction between exit codes 126 and 127 is based on KornShell practice that uses 127 when all attempts to
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<i>exec</i> the utility fail with [ENOENT], and uses 126 when any attempt to <i>exec</i> the utility fails for any other
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reason.</p>
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<p>Historical implementations of the <i>env</i> utility use the <a href="../functions/execvp.html"><i>execvp</i>()</a> or <a href=
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"../functions/execlp.html"><i>execlp</i>()</a> functions defined in the System Interfaces volume of IEEE Std 1003.1-2001
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to invoke the specified utility; this provides better performance and keeps users from having to escape characters with special
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meaning to the shell. Therefore, shell functions, special built-ins, and built-ins that are only provided by the shell are not
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found.</p>
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</blockquote>
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<h4><a name="tag_04_43_17"></a>EXAMPLES</h4>
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<blockquote>
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<p>The following command:</p>
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<pre>
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<tt>env -i PATH=/mybin mygrep xyz myfile
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</tt>
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</pre>
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<p>invokes the command <i>mygrep</i> with a new <i>PATH</i> value as the only entry in its environment. In this case, <i>PATH</i>
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is used to locate <i>mygrep</i>, which then must reside in <b>/mybin</b>.</p>
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</blockquote>
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<h4><a name="tag_04_43_18"></a>RATIONALE</h4>
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<blockquote>
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<p>As with all other utilities that invoke other utilities, this volume of IEEE Std 1003.1-2001 only specifies what
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<i>env</i> does with standard input, standard output, standard error, input files, and output files. If a utility is executed, it
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is not constrained by the specification of input and output by <i>env</i>.</p>
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<p>The <b>-i</b> option was added to allow the functionality of the withdrawn <b>-</b> option in a manner compatible with the
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Utility Syntax Guidelines.</p>
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<p>Some have suggested that <i>env</i> is redundant since the same effect is achieved by:</p>
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<pre>
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<tt>name=value ... utility</tt> <b>[</b> <tt>argument ...</tt> <b>]</b>
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</pre>
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<p>The example is equivalent to <i>env</i> when an environment variable is being added to the environment of the command, but not
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when the environment is being set to the given value. The <i>env</i> utility also writes out the current environment if invoked
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without arguments. There is sufficient functionality beyond what the example provides to justify inclusion of <i>env</i>.</p>
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</blockquote>
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<h4><a name="tag_04_43_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_43_20"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="xcu_chap02.html#tag_02_05"><i>Parameters and Variables</i></a> , <a href="xcu_chap02.html#tag_02_14"><i>Special
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Built-In Utilities</i></a></p>
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</blockquote>
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<h4><a name="tag_04_43_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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<div class="box"><em>End of informative text.</em></div>
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<hr>
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POSIX ® is a registered Trademark of The IEEE.<br>
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