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<title>Comparing and Merging Files: Adjusting Output</title>

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<a name="Adjusting-Output"></a>
<div class="header">
<p>
Next: <a href="diff-Performance.html#diff-Performance" accesskey="n" rel="next">diff Performance</a>, Previous: <a href="Comparing-Directories.html#Comparing-Directories" accesskey="p" rel="prev">Comparing Directories</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="Making-diff-Output-Prettier"></a>
<h2 class="chapter">5 Making <code>diff</code> Output Prettier</h2>

<p><code>diff</code> provides several ways to adjust the appearance of its output.
These adjustments can be applied to any output format.
</p>
<table class="menu" border="0" cellspacing="0">
<tr><td align="left" valign="top">&bull; <a href="#Tabs" accesskey="1">Tabs</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Preserving the alignment of tab stops.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="#Trailing-Blanks" accesskey="2">Trailing Blanks</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Suppressing blanks before empty output lines.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="#Pagination" accesskey="3">Pagination</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Page numbering and time-stamping <code>diff</code> output.
</td></tr>
</table>

<hr>
<a name="Tabs"></a>
<div class="header">
<p>
Next: <a href="#Trailing-Blanks" accesskey="n" rel="next">Trailing Blanks</a>, Up: <a href="#Adjusting-Output" accesskey="u" rel="up">Adjusting Output</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="Preserving-Tab-Stop-Alignment"></a>
<h3 class="section">5.1 Preserving Tab Stop Alignment</h3>
<a name="index-tab-stop-alignment"></a>
<a name="index-aligning-tab-stops"></a>

<p>The lines of text in some of the <code>diff</code> output formats are
preceded by one or two characters that indicate whether the text is
inserted, deleted, or changed.  The addition of those characters can
cause tabs to move to the next tab stop, throwing off the alignment of
columns in the line.  <acronym>GNU</acronym> <code>diff</code> provides two ways
to make tab-aligned columns line up correctly.
</p>
<p>The first way is to have <code>diff</code> convert all tabs into the correct
number of spaces before outputting them; select this method with the
<samp>--expand-tabs</samp> (<samp>-t</samp>) option.  To use this form of output with
<code>patch</code>, you must give <code>patch</code> the <samp>-l</samp> or
<samp>--ignore-white-space</samp> option (see <a href="Merging-with-patch.html#Changed-White-Space">Changed White Space</a>, for more
information).  <code>diff</code> normally assumes that tab stops are set
every 8 print columns, but this can be altered by the
<samp>--tabsize=<var>columns</var></samp> option.
</p>
<p>The other method for making tabs line up correctly is to add a tab
character instead of a space after the indicator character at the
beginning of the line.  This ensures that all following tab characters
are in the same position relative to tab stops that they were in the
original files, so that the output is aligned correctly.  Its
disadvantage is that it can make long lines too long to fit on one line
of the screen or the paper.  It also does not work with the unified
output format, which does not have a space character after the change
type indicator character.  Select this method with the <samp>-T</samp> or
<samp>--initial-tab</samp> option.
</p>
<hr>
<a name="Trailing-Blanks"></a>
<div class="header">
<p>
Next: <a href="#Pagination" accesskey="n" rel="next">Pagination</a>, Previous: <a href="#Tabs" accesskey="p" rel="prev">Tabs</a>, Up: <a href="#Adjusting-Output" accesskey="u" rel="up">Adjusting Output</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="Omitting-trailing-blanks"></a>
<h3 class="section">5.2 Omitting trailing blanks</h3>
<a name="index-trailing-blanks"></a>
<p>When outputting lines in normal or context format, or outputting an
unchanged line in unified format, <code>diff</code> normally outputs a
blank just before each line.  If the line is empty, the output of
<code>diff</code> therefore contains trailing blanks even though the
input does not contain them.  For example, when outputting an
unchanged empty line in context format, <code>diff</code> normally
outputs a line with two leading spaces.
</p>
<p>Some text editors and email agents routinely delete trailing blanks,
so it can be a problem to deal with diff output files that contain
them.  You can avoid this problem with the
<samp>--suppress-blank-empty</samp> option.  It causes <code>diff</code> to
omit trailing blanks at the end of output lines in normal, context,
and unified format, unless the trailing blanks were already present in
the input.  This changes the output format slightly, so that output
lines are guaranteed to never end in a blank unless an input line ends
in a blank.  This format is less likely to be munged by text editors
or by transmission via email.  It is accepted by <acronym>GNU</acronym>
<code>patch</code> as well.
</p>
<hr>
<a name="Pagination"></a>
<div class="header">
<p>
Previous: <a href="#Trailing-Blanks" accesskey="p" rel="prev">Trailing Blanks</a>, Up: <a href="#Adjusting-Output" accesskey="u" rel="up">Adjusting Output</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="Paginating-diff-Output"></a>
<h3 class="section">5.3 Paginating <code>diff</code> Output</h3>
<a name="index-paginating-diff-output"></a>

<p>It can be convenient to have long output page-numbered and time-stamped.
The <samp>--paginate</samp> (<samp>-l</samp>) option does this by sending the
<code>diff</code> output through the <code>pr</code> program.  Here is what the page
header might look like for &lsquo;<samp>diff -lc lao tzu</samp>&rsquo;:
</p>
<div class="example">
<pre class="example">2002-02-22 14:20                 diff -lc lao tzu                 Page 1
</pre></div>

<hr>
<div class="header">
<p>
Previous: <a href="#Trailing-Blanks" accesskey="p" rel="prev">Trailing Blanks</a>, Up: <a href="#Adjusting-Output" accesskey="u" rel="up">Adjusting Output</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>
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