/usr/share/doc/diffutils-doc/Invoking-cmp.html

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<title>Comparing and Merging Files: Invoking cmp</title>

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<a name="Invoking-cmp"></a>
<div class="header">
<p>
Next: <a href="Invoking-diff.html#Invoking-diff" accesskey="n" rel="next">Invoking diff</a>, Previous: <a href="Making-Patches.html#Making-Patches" accesskey="p" rel="prev">Making Patches</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index.html#Index" title="Index" rel="index">Index</a>]</p>
</div>
<a name="Invoking-cmp-1"></a>
<h2 class="chapter">12 Invoking <code>cmp</code></h2>
<a name="index-invoking-cmp"></a>
<a name="index-cmp-invocation"></a>

<p>The <code>cmp</code> command compares two files, and if they differ,
tells the first byte and line number where they differ or reports
that one file is a prefix of the other.  Bytes and
lines are numbered starting with 1.  The arguments of <code>cmp</code>
are as follows:
</p>
<div class="example">
<pre class="example">cmp <var>options</var>&hellip; <var>from-file</var> <span class="roman">[</span><var>to-file</var> <span class="roman">[</span><var>from-skip</var> <span class="roman">[</span><var>to-skip</var><span class="roman">]</span><span class="roman">]</span><span class="roman">]</span>
</pre></div>

<p>The file name <samp>-</samp> is always the standard input.  <code>cmp</code>
also uses the standard input if one file name is omitted.  The
<var>from-skip</var> and <var>to-skip</var> operands specify how many bytes to
ignore at the start of each file; they are equivalent to the
<samp>--ignore-initial=<var>from-skip</var>:<var>to-skip</var></samp> option.
</p>
<p>By default, <code>cmp</code> outputs nothing if the two files have the
same contents.  If one file is a prefix of the other, <code>cmp</code>
prints to standard error a message of the following form:
</p>
<div class="example">
<pre class="example">cmp: EOF on <var>shorter-file</var>
</pre></div>

<p>Otherwise, <code>cmp</code> prints to standard output a message of the
following form:
</p>
<div class="example">
<pre class="example"><var>from-file</var> <var>to-file</var> differ: char <var>byte-number</var>, line <var>line-number</var>
</pre></div>

<p>The message formats can differ outside the <acronym>POSIX</acronym> locale.
Also, <acronym>POSIX</acronym> allows the <acronym>EOF</acronym> message to be followed
by a blank and some additional information.
</p>
<p>An exit status of 0 means no differences were found, 1 means some
differences were found, and 2 means trouble.
</p>
<table class="menu" border="0" cellspacing="0">
<tr><td align="left" valign="top">&bull; <a href="#cmp-Options" accesskey="1">cmp Options</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Summary of options to <code>cmp</code>.
</td></tr>
</table>

<hr>
<a name="cmp-Options"></a>
<div class="header">
<p>
Up: <a href="#Invoking-cmp" accesskey="u" rel="up">Invoking cmp</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index.html#Index" title="Index" rel="index">Index</a>]</p>
</div>
<a name="Options-to-cmp"></a>
<h3 class="section">12.1 Options to <code>cmp</code></h3>
<a name="index-cmp-options"></a>
<a name="index-options-for-cmp"></a>

<p>Below is a summary of all of the options that <acronym>GNU</acronym>
<code>cmp</code> accepts.  Most options have two equivalent names, one of
which is a single letter preceded by &lsquo;<samp>-</samp>&rsquo;, and the other of which
is a long name preceded by &lsquo;<samp>--</samp>&rsquo;.  Multiple single letter options
(unless they take an argument) can be combined into a single command
line word: <samp>-bl</samp> is equivalent to <samp>-b -l</samp>.
</p>
<dl compact="compact">
<dt><samp>-b</samp></dt>
<dt><samp>--print-bytes</samp></dt>
<dd><p>Print the differing bytes.  Display control bytes as a
&lsquo;<samp>^</samp>&rsquo; followed by a letter of the alphabet and precede bytes
that have the high bit set with &lsquo;<samp>M-</samp>&rsquo; (which stands for &ldquo;meta&rdquo;).
</p>
</dd>
<dt><samp>--help</samp></dt>
<dd><p>Output a summary of usage and then exit.
</p>
</dd>
<dt><samp>-i <var>skip</var></samp></dt>
<dt><samp>--ignore-initial=<var>skip</var></samp></dt>
<dd><p>Ignore any differences in the first <var>skip</var> bytes of the input
files.  Treat files with fewer than <var>skip</var> bytes as if they are
empty.  If <var>skip</var> is of the form
<samp><var>from-skip</var>:<var>to-skip</var></samp>, skip the first <var>from-skip</var>
bytes of the first input file and the first <var>to-skip</var> bytes of the
second.
</p>
</dd>
<dt><samp>-l</samp></dt>
<dt><samp>--verbose</samp></dt>
<dd><p>Output the (decimal) byte numbers and (octal) values of all differing bytes,
instead of the default standard output.
Each output line contains a differing byte&rsquo;s number relative to the
start of the input, followed by the differing byte values.
Byte numbers start at 1.
Also, output the <acronym>EOF</acronym> message if one file is shorter than the other.
</p>
</dd>
<dt><samp>-n <var>count</var></samp></dt>
<dt><samp>--bytes=<var>count</var></samp></dt>
<dd><p>Compare at most <var>count</var> input bytes.
</p>
</dd>
<dt><samp>-s</samp></dt>
<dt><samp>--quiet</samp></dt>
<dt><samp>--silent</samp></dt>
<dd><p>Do not print anything; only return an exit status indicating whether
the files differ.
</p>
</dd>
<dt><samp>-v</samp></dt>
<dt><samp>--version</samp></dt>
<dd><p>Output version information and then exit.
</p></dd>
</dl>

<p>In the above table, operands that are byte counts are normally
decimal, but may be preceded by &lsquo;<samp>0</samp>&rsquo; for octal and &lsquo;<samp>0x</samp>&rsquo; for
hexadecimal.
</p>
<p>A byte count can be followed by a suffix to specify a multiple of that
count; in this case an omitted integer is understood to be 1.  A bare
size letter, or one followed by &lsquo;<samp>iB</samp>&rsquo;, specifies a multiple using
powers of 1024.  A size letter followed by &lsquo;<samp>B</samp>&rsquo; specifies powers
of 1000 instead.  For example, <samp>-n 4M</samp> and <samp>-n 4MiB</samp> are
equivalent to <samp>-n 4194304</samp>, whereas <samp>-n 4MB</samp> is
equivalent to <samp>-n 4000000</samp>.  This notation is upward compatible
with the <a href="http://www.bipm.fr/enus/3_SI/si-prefixes.html">SI
prefixes</a> for decimal multiples and with the
<a href="http://physics.nist.gov/cuu/Units/binary.html">IEC 60027-2
prefixes for binary multiples</a>.
</p>
<p>The following suffixes are defined.  Large sizes like <code>1Y</code> may be
rejected by your computer due to limitations of its arithmetic.
</p>
<dl compact="compact">
<dt>&lsquo;<samp>kB</samp>&rsquo;</dt>
<dd><a name="index-kilobyte_002c-definition-of"></a>
<p>kilobyte: <em>10^3 = 1000</em>.
</p></dd>
<dt>&lsquo;<samp>k</samp>&rsquo;</dt>
<dt>&lsquo;<samp>K</samp>&rsquo;</dt>
<dt>&lsquo;<samp>KiB</samp>&rsquo;</dt>
<dd><a name="index-kibibyte_002c-definition-of"></a>
<p>kibibyte: <em>2^10 = 1024</em>.  &lsquo;<samp>K</samp>&rsquo; is special: the SI prefix is
&lsquo;<samp>k</samp>&rsquo; and the IEC 60027-2 prefix is &lsquo;<samp>Ki</samp>&rsquo;, but tradition and
<acronym>POSIX</acronym> use &lsquo;<samp>k</samp>&rsquo; to mean &lsquo;<samp>KiB</samp>&rsquo;.
</p></dd>
<dt>&lsquo;<samp>MB</samp>&rsquo;</dt>
<dd><a name="index-megabyte_002c-definition-of"></a>
<p>megabyte: <em>10^6 = 1,000,000</em>.
</p></dd>
<dt>&lsquo;<samp>M</samp>&rsquo;</dt>
<dt>&lsquo;<samp>MiB</samp>&rsquo;</dt>
<dd><a name="index-mebibyte_002c-definition-of"></a>
<p>mebibyte: <em>2^20 = 1,048,576</em>.
</p></dd>
<dt>&lsquo;<samp>GB</samp>&rsquo;</dt>
<dd><a name="index-gigabyte_002c-definition-of"></a>
<p>gigabyte: <em>10^9 = 1,000,000,000</em>.
</p></dd>
<dt>&lsquo;<samp>G</samp>&rsquo;</dt>
<dt>&lsquo;<samp>GiB</samp>&rsquo;</dt>
<dd><a name="index-gibibyte_002c-definition-of"></a>
<p>gibibyte: <em>2^30 = 1,073,741,824</em>.
</p></dd>
<dt>&lsquo;<samp>TB</samp>&rsquo;</dt>
<dd><a name="index-terabyte_002c-definition-of"></a>
<p>terabyte:  <em>10^12 = 1,000,000,000,000</em>.
</p></dd>
<dt>&lsquo;<samp>T</samp>&rsquo;</dt>
<dt>&lsquo;<samp>TiB</samp>&rsquo;</dt>
<dd><a name="index-tebibyte_002c-definition-of"></a>
<p>tebibyte: <em>2^40 = 1,099,511,627,776</em>.
</p></dd>
<dt>&lsquo;<samp>PB</samp>&rsquo;</dt>
<dd><a name="index-petabyte_002c-definition-of"></a>
<p>petabyte: <em>10^15 = 1,000,000,000,000,000</em>.
</p></dd>
<dt>&lsquo;<samp>P</samp>&rsquo;</dt>
<dt>&lsquo;<samp>PiB</samp>&rsquo;</dt>
<dd><a name="index-pebibyte_002c-definition-of"></a>
<p>pebibyte: <em>2^50 = 1,125,899,906,842,624</em>.
</p></dd>
<dt>&lsquo;<samp>EB</samp>&rsquo;</dt>
<dd><a name="index-exabyte_002c-definition-of"></a>
<p>exabyte: <em>10^18 = 1,000,000,000,000,000,000</em>.
</p></dd>
<dt>&lsquo;<samp>E</samp>&rsquo;</dt>
<dt>&lsquo;<samp>EiB</samp>&rsquo;</dt>
<dd><a name="index-exbibyte_002c-definition-of"></a>
<p>exbibyte: <em>2^60 = 1,152,921,504,606,846,976</em>.
</p></dd>
<dt>&lsquo;<samp>ZB</samp>&rsquo;</dt>
<dd><a name="index-zettabyte_002c-definition-of"></a>
<p>zettabyte: <em>10^21 = 1,000,000,000,000,000,000,000</em>
</p></dd>
<dt>&lsquo;<samp>Z</samp>&rsquo;</dt>
<dt>&lsquo;<samp>ZiB</samp>&rsquo;</dt>
<dd><p><em>2^70 = 1,180,591,620,717,411,303,424</em>.
(&lsquo;<samp>Zi</samp>&rsquo; is a GNU extension to IEC 60027-2.)
</p></dd>
<dt>&lsquo;<samp>YB</samp>&rsquo;</dt>
<dd><a name="index-yottabyte_002c-definition-of"></a>
<p>yottabyte: <em>10^24 = 1,000,000,000,000,000,000,000,000</em>.
</p></dd>
<dt>&lsquo;<samp>Y</samp>&rsquo;</dt>
<dt>&lsquo;<samp>YiB</samp>&rsquo;</dt>
<dd><p><em>2^80 = 1,208,925,819,614,629,174,706,176</em>.
(&lsquo;<samp>Yi</samp>&rsquo; is a GNU extension to IEC 60027-2.)
</p></dd>
</dl>

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