sort.html

IEEE 1003.1-2003, Single Unix Specification v3

<pre>
<i>field_number</i><b>[</b><tt>.</tt><i>first_character</i><b>]</b>
</pre>

<p>Fields and characters within fields shall be numbered starting with 1. The <i>field_number</i> and <i>first_character</i>
pieces, interpreted as positive decimal integers, shall specify the first character to be used as part of a sort key. If
<i>.first_character</i> is omitted, it shall refer to the first character of the field.</p>

<p>The <i>field_end</i> portion of the <i>keydef</i> option-argument shall have the form:</p>

<pre>
<i>field_number</i><b>[</b><tt>.</tt><i>last_character</i><b>]</b>
</pre>

<p>The <i>field_number</i> shall be as described above for <i>field_start.</i> The <i>last_character</i> piece, interpreted as a
non-negative decimal integer, shall specify the last character to be used as part of the sort key. If <i>last_character</i>
evaluates to zero or <i>.last_character</i> is omitted, it shall refer to the last character of the field specified by
<i>field_number</i>.</p>

<p>If the <b>-b</b> option or <b>b</b> type modifier is in effect, characters within a field shall be counted from the first non-
&lt;blank&gt; in the field. (This shall apply separately to <i>first_character</i> and <i>last_character</i>.)</p>
</blockquote>

<h4><a name="tag_04_131_14"></a>EXIT STATUS</h4>

<blockquote>
<p>The following exit values shall be returned:</p>

<dl compact>
<dt>&nbsp;0</dt>

<dd>All input files were output successfully, or <b>-c</b> was specified and the input file was correctly sorted.</dd>

<dt>&nbsp;1</dt>

<dd>Under the <b>-c</b> option, the file was not ordered as specified, or if the <b>-c</b> and <b>-u</b> options were both
specified, two input lines were found with equal keys.</dd>

<dt>&gt;1</dt>

<dd>An error occurred.</dd>
</dl>
</blockquote>

<h4><a name="tag_04_131_15"></a>CONSEQUENCES OF ERRORS</h4>

<blockquote>
<p>Default.</p>
</blockquote>

<hr>
<div class="box"><em>The following sections are informative.</em></div>

<h4><a name="tag_04_131_16"></a>APPLICATION USAGE</h4>

<blockquote>
<p>The default value for <b>-t</b>, &lt;blank&gt;, has different properties from, for example, <b>-t</b> "&lt;space&gt;". If a line
contains:</p>

<pre>
<tt>&lt;space&gt;&lt;space&gt;foo
</tt>
</pre>

<p>the following treatment would occur with default separation as opposed to specifically selecting a &lt;space&gt;:</p>

<center>
<table border="1" cellpadding="3" align="center">
<tr valign="top">
<th align="center">
<p class="tent"><b>Field</b></p>
</th>
<th align="center">
<p class="tent"><b>Default</b></p>
</th>
<th align="center">
<p class="tent"><b>-t "&lt;space&gt;"</b></p>
</th>
</tr>

<tr valign="top">
<td align="left">
<p class="tent">1</p>
</td>
<td align="left">
<p class="tent">&lt;space&gt;&lt;space&gt;foo</p>
</td>
<td align="left">
<p class="tent"><i>empty</i></p>
</td>
</tr>

<tr valign="top">
<td align="left">
<p class="tent">2</p>
</td>
<td align="left">
<p class="tent"><i>empty</i></p>
</td>
<td align="left">
<p class="tent"><i>empty</i></p>
</td>
</tr>

<tr valign="top">
<td align="left">
<p class="tent">3</p>
</td>
<td align="left">
<p class="tent"><i>empty</i></p>
</td>
<td align="left">
<p class="tent">foo</p>
</td>
</tr>
</table>
</center>

<p>The leading field separator itself is included in a field when <b>-t</b> is not used. For example, this command returns an exit
status of zero, meaning the input was already sorted:</p>

<pre>
<tt>sort -c -k 2 &lt;&lt;eof
y&lt;tab&gt;b
x&lt;space&gt;a
eof
</tt>
</pre>

<p>(assuming that a &lt;tab&gt; precedes the &lt;space&gt; in the current collating sequence). The field separator is not included
in a field when it is explicitly set via <b>-t</b>. This is historical practice and allows usage such as:</p>

<pre>
<tt>sort -t "|" -k 2n &lt;&lt;eof
Atlanta|425022|Georgia
Birmingham|284413|Alabama
Columbia|100385|South Carolina
eof
</tt>
</pre>

<p>where the second field can be correctly sorted numerically without regard to the non-numeric field separator.</p>

<p>The wording in the OPTIONS section clarifies that the <b>-b</b>, <b>-d</b>, <b>-f</b>, <b>-i</b>, <b>-n</b>, and <b>-r</b>
options have to come before the first sort key specified if they are intended to apply to all specified keys. The way it is
described in this volume of IEEE&nbsp;Std&nbsp;1003.1-2001 matches historical practice, not historical documentation. The results
are unspecified if these options are specified after a <b>-k</b> option.</p>

<p>The <b>-f</b> option might not work as expected in locales where there is not a one-to-one mapping between an uppercase and a
lowercase letter.</p>
</blockquote>

<h4><a name="tag_04_131_17"></a>EXAMPLES</h4>

<blockquote>
<ol>
<li>
<p>The following command sorts the contents of <b>infile</b> with the second field as the sort key:</p>

<pre>
<tt>sort -k 2,2 infile
</tt>
</pre>
</li>

<li>
<p>The following command sorts, in reverse order, the contents of <b>infile1</b> and <b>infile2</b>, placing the output in
<b>outfile</b> and using the second character of the second field as the sort key (assuming that the first character of the second
field is the field separator):</p>

<pre>
<tt>sort -r -o outfile -k 2.2,2.2 infile1 infile2
</tt>
</pre>
</li>

<li>
<p>The following command sorts the contents of <b>infile1</b> and <b>infile2</b> using the second non- &lt;blank&gt; of the second
field as the sort key:</p>

<pre>
<tt>sort -k 2.2b,2.2b infile1 infile2
</tt>
</pre>
</li>

<li>
<p>The following command prints the System&nbsp;V password file (user database) sorted by the numeric user ID (the third
colon-separated field):</p>

<pre>
<tt>sort -t : -k 3,3n /etc/passwd
</tt>
</pre>
</li>

<li>
<p>The following command prints the lines of the already sorted file <b>infile</b>, suppressing all but one occurrence of lines
having the same third field:</p>

<pre>
<tt>sort -um -k 3.1,3.0 infile
</tt>
</pre>
</li>
</ol>
</blockquote>

<h4><a name="tag_04_131_18"></a>RATIONALE</h4>

<blockquote>
<p>Examples in some historical documentation state that options <b>-um</b> with one input file keep the first in each set of lines
with equal keys. This behavior was deemed to be an implementation artifact and was not standardized.</p>

<p>The <b>-z</b> option was omitted; it is not standard practice on most systems and is inconsistent with using <i>sort</i> to sort
several files individually and then merge them together. The text concerning <b>-z</b> in historical documentation appeared to
require implementations to determine the proper buffer length during the sort phase of operation, but not during the merge.</p>

<p>The <b>-y</b> option was omitted because of non-portability. The <b>-M</b> option, present in System V, was omitted because of
non-portability in international usage.</p>

<p>An undocumented <b>-T</b> option exists in some implementations. It is used to specify a directory for intermediate files.
Implementations are encouraged to support the use of the <i>TMPDIR</i> environment variable instead of adding an option to support
this functionality.</p>

<p>The <b>-k</b> option was added to satisfy two objections. First, the zero-based counting used by <i>sort</i> is not consistent
with other utility conventions. Second, it did not meet syntax guideline requirements.</p>

<p>Historical documentation indicates that &quot;setting <b>-n</b> implies <b>-b</b>&quot;. The description of <b>-n</b> already states
that optional leading &lt;blank&gt;s are tolerated in doing the comparison. If <b>-b</b> is enabled, rather than implied, by
<b>-n</b>, this has unusual side effects. When a character offset is used in a column of numbers (for example, to sort modulo 100),
that offset is measured relative to the most significant digit, not to the column. Based upon a recommendation from the author of
the original <i>sort</i> utility, the <b>-b</b> implication has been omitted from this volume of IEEE&nbsp;Std&nbsp;1003.1-2001,
and an application wishing to achieve the previously mentioned side effects has to code the <b>-b</b> flag explicitly.</p>
</blockquote>

<h4><a name="tag_04_131_19"></a>FUTURE DIRECTIONS</h4>

<blockquote>
<p>None.</p>
</blockquote>

<h4><a name="tag_04_131_20"></a>SEE ALSO</h4>

<blockquote>
<p><a href="comm.html"><i>comm</i></a> , <a href="join.html"><i>join</i></a> , <a href="uniq.html"><i>uniq</i></a> , the System
Interfaces volume of IEEE&nbsp;Std&nbsp;1003.1-2001, <a href="../functions/toupper.html"><i>toupper</i>()</a></p>
</blockquote>

<h4><a name="tag_04_131_21"></a>CHANGE HISTORY</h4>

<blockquote>
<p>First released in Issue 2.</p>
</blockquote>

<h4><a name="tag_04_131_22"></a>Issue 6</h4>

<blockquote>
<p>IEEE PASC Interpretation 1003.2 #174 is applied, updating the DESCRIPTION of comparisons.</p>

<p>IEEE PASC Interpretation 1003.2 #168 is applied.</p>
</blockquote>

<div class="box"><em>End of informative text.</em></div>

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