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<body lang="en">
<a name="Projects"></a>
<div class="header">
<p>
Next: <a href="Copying-This-Manual.html#Copying-This-Manual" accesskey="n" rel="next">Copying This Manual</a>, Previous: <a href="Standards-conformance.html#Standards-conformance" accesskey="p" rel="prev">Standards conformance</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="Future-Projects"></a>
<h2 class="chapter">18 Future Projects</h2>

<p>Here are some ideas for improving <acronym>GNU</acronym> <code>diff</code> and
<code>patch</code>.  The <acronym>GNU</acronym> project has identified some
improvements as potential programming projects for volunteers.  You
can also help by reporting any bugs that you find.
</p>
<p>If you are a programmer and would like to contribute something to the
<acronym>GNU</acronym> project, please consider volunteering for one of these
projects.  If you are seriously contemplating work, please write to
<a href="mailto:gvc@gnu.org">gvc@gnu.org</a> to coordinate with other volunteers.
</p>
<table class="menu" border="0" cellspacing="0">
<tr><td align="left" valign="top">&bull; <a href="#Shortcomings" accesskey="1">Shortcomings</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Suggested projects for improvements.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="#Bugs" accesskey="2">Bugs</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Reporting bugs.
</td></tr>
</table>

<hr>
<a name="Shortcomings"></a>
<div class="header">
<p>
Next: <a href="#Bugs" accesskey="n" rel="next">Bugs</a>, Up: <a href="#Projects" accesskey="u" rel="up">Projects</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="Suggested-Projects-for-Improving-GNU-diff-and-patch"></a>
<h3 class="section">18.1 Suggested Projects for Improving <acronym>GNU</acronym> <code>diff</code> and <code>patch</code></h3>
<a name="index-projects-for-directories"></a>

<p>One should be able to use <acronym>GNU</acronym> <code>diff</code> to generate a
patch from any pair of directory trees, and given the patch and a copy
of one such tree, use <code>patch</code> to generate a faithful copy of
the other.  Unfortunately, some changes to directory trees cannot be
expressed using current patch formats; also, <code>patch</code> does not
handle some of the existing formats.  These shortcomings motivate the
following suggested projects.
</p>
<table class="menu" border="0" cellspacing="0">
<tr><td align="left" valign="top">&bull; <a href="#Internationalization" accesskey="1">Internationalization</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Handling multibyte and varying-width characters.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="#Changing-Structure" accesskey="2">Changing Structure</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Handling changes to the directory structure.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="#Special-Files" accesskey="3">Special Files</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Handling symbolic links, device special files, etc.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="#Unusual-File-Names" accesskey="4">Unusual File Names</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Handling file names that contain unusual characters.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="#Time-Stamp-Order" accesskey="5">Time Stamp Order</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Outputting diffs in time stamp order.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="#Ignoring-Changes" accesskey="6">Ignoring Changes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Ignoring certain changes while showing others.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="#Speedups" accesskey="7">Speedups</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Improving performance.
</td></tr>
</table>

<hr>
<a name="Internationalization"></a>
<div class="header">
<p>
Next: <a href="#Changing-Structure" accesskey="n" rel="next">Changing Structure</a>, Up: <a href="#Shortcomings" accesskey="u" rel="up">Shortcomings</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="Handling-Multibyte-and-Varying_002dWidth-Characters"></a>
<h4 class="subsection">18.1.1 Handling Multibyte and Varying-Width Characters</h4>
<a name="index-multibyte-characters"></a>
<a name="index-varying_002dwidth-characters"></a>

<p><code>diff</code>, <code>diff3</code> and <code>sdiff</code> treat each line of
input as a string of unibyte characters.  This can mishandle multibyte
characters in some cases.  For example, when asked to ignore spaces,
<code>diff</code> does not properly ignore a multibyte space character.
</p>
<p>Also, <code>diff</code> currently assumes that each byte is one column
wide, and this assumption is incorrect in some locales, e.g., locales
that use UTF-8 encoding.  This causes problems with the <samp>-y</samp> or
<samp>--side-by-side</samp> option of <code>diff</code>.
</p>
<p>These problems need to be fixed without unduly affecting the
performance of the utilities in unibyte environments.
</p>
<p>The IBM GNU/Linux Technology Center Internationalization Team has
proposed
<a href="http://oss.software.ibm.com/developer/opensource/linux/patches/i18n/diffutils-2.7.2-i18n-0.1.patch.gz">patches
to support internationalized <code>diff</code></a>.
Unfortunately, these patches are incomplete and are to an older
version of <code>diff</code>, so more work needs to be done in this area.
</p>
<hr>
<a name="Changing-Structure"></a>
<div class="header">
<p>
Next: <a href="#Special-Files" accesskey="n" rel="next">Special Files</a>, Previous: <a href="#Internationalization" accesskey="p" rel="prev">Internationalization</a>, Up: <a href="#Shortcomings" accesskey="u" rel="up">Shortcomings</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="Handling-Changes-to-the-Directory-Structure"></a>
<h4 class="subsection">18.1.2 Handling Changes to the Directory Structure</h4>
<a name="index-directory-structure-changes"></a>

<p><code>diff</code> and <code>patch</code> do not handle some changes to directory
structure.  For example, suppose one directory tree contains a directory
named &lsquo;<samp>D</samp>&rsquo; with some subsidiary files, and another contains a file
with the same name &lsquo;<samp>D</samp>&rsquo;.  &lsquo;<samp>diff -r</samp>&rsquo; does not output enough
information for <code>patch</code> to transform the directory subtree into
the file.
</p>
<p>There should be a way to specify that a file has been removed without
having to include its entire contents in the patch file.  There should
also be a way to tell <code>patch</code> that a file was renamed, even if
there is no way for <code>diff</code> to generate such information.
There should be a way to tell <code>patch</code> that a file&rsquo;s time stamp
has changed, even if its contents have not changed.
</p>
<p>These problems can be fixed by extending the <code>diff</code> output format
to represent changes in directory structure, and extending <code>patch</code>
to understand these extensions.
</p>
<hr>
<a name="Special-Files"></a>
<div class="header">
<p>
Next: <a href="#Unusual-File-Names" accesskey="n" rel="next">Unusual File Names</a>, Previous: <a href="#Changing-Structure" accesskey="p" rel="prev">Changing Structure</a>, Up: <a href="#Shortcomings" accesskey="u" rel="up">Shortcomings</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="Files-that-are-Neither-Directories-Nor-Regular-Files"></a>
<h4 class="subsection">18.1.3 Files that are Neither Directories Nor Regular Files</h4>
<a name="index-special-files"></a>

<p>Some files are neither directories nor regular files: they are unusual
files like symbolic links, device special files, named pipes, and
sockets.  Currently, <code>diff</code> treats symbolic links as if they
were the pointed-to files, except that a recursive <code>diff</code>
reports an error if it detects infinite loops of symbolic links (e.g.,
symbolic links to <samp>..</samp>).  <code>diff</code> treats other special
files like regular files if they are specified at the top level, but
simply reports their presence when comparing directories.  This means
that <code>patch</code> cannot represent changes to such files.  For
example, if you change which file a symbolic link points to,
<code>diff</code> outputs the difference between the two files, instead
of the change to the symbolic link.
</p>
<p><code>diff</code> should optionally report changes to special files specially,
and <code>patch</code> should be extended to understand these extensions.
</p>
<hr>
<a name="Unusual-File-Names"></a>
<div class="header">
<p>
Next: <a href="#Time-Stamp-Order" accesskey="n" rel="next">Time Stamp Order</a>, Previous: <a href="#Special-Files" accesskey="p" rel="prev">Special Files</a>, Up: <a href="#Shortcomings" accesskey="u" rel="up">Shortcomings</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="File-Names-that-Contain-Unusual-Characters"></a>
<h4 class="subsection">18.1.4 File Names that Contain Unusual Characters</h4>
<a name="index-file-names-with-unusual-characters"></a>

<p>When a file name contains an unusual character like a newline or
white space, &lsquo;<samp>diff -r</samp>&rsquo; generates a patch that <code>patch</code> cannot
parse.  The problem is with format of <code>diff</code> output, not just with
<code>patch</code>, because with odd enough file names one can cause
<code>diff</code> to generate a patch that is syntactically correct but
patches the wrong files.  The format of <code>diff</code> output should be
extended to handle all possible file names.
</p>
<hr>
<a name="Time-Stamp-Order"></a>
<div class="header">
<p>
Next: <a href="#Ignoring-Changes" accesskey="n" rel="next">Ignoring Changes</a>, Previous: <a href="#Unusual-File-Names" accesskey="p" rel="prev">Unusual File Names</a>, Up: <a href="#Shortcomings" accesskey="u" rel="up">Shortcomings</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="Outputting-Diffs-in-Time-Stamp-Order"></a>
<h4 class="subsection">18.1.5 Outputting Diffs in Time Stamp Order</h4>

<p>Applying <code>patch</code> to a multiple-file diff can result in files
whose time stamps are out of order.  <acronym>GNU</acronym> <code>patch</code> has
options to restore the time stamps of the updated files
(see <a href="Merging-with-patch.html#Patching-Time-Stamps">Patching Time Stamps</a>), but sometimes it is useful to generate
a patch that works even if the recipient does not have <acronym>GNU</acronym> patch,
or does not use these options.  One way to do this would be to
implement a <code>diff</code> option to output diffs in time stamp order.
</p>
<hr>
<a name="Ignoring-Changes"></a>
<div class="header">
<p>
Next: <a href="#Speedups" accesskey="n" rel="next">Speedups</a>, Previous: <a href="#Time-Stamp-Order" accesskey="p" rel="prev">Time Stamp Order</a>, Up: <a href="#Shortcomings" accesskey="u" rel="up">Shortcomings</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="Ignoring-Certain-Changes"></a>
<h4 class="subsection">18.1.6 Ignoring Certain Changes</h4>

<p>It would be nice to have a feature for specifying two strings, one in
<var>from-file</var> and one in <var>to-file</var>, which should be considered to
match.  Thus, if the two strings are &lsquo;<samp>foo</samp>&rsquo; and &lsquo;<samp>bar</samp>&rsquo;, then if
two lines differ only in that &lsquo;<samp>foo</samp>&rsquo; in file 1 corresponds to
&lsquo;<samp>bar</samp>&rsquo; in file 2, the lines are treated as identical.
</p>
<p>It is not clear how general this feature can or should be, or
what syntax should be used for it.
</p>
<p>A partial substitute is to filter one or both files before comparing,
e.g.:
</p>
<div class="example">
<pre class="example">sed 's/foo/bar/g' file1 | diff - file2
</pre></div>

<p>However, this outputs the filtered text, not the original.
</p>
<hr>
<a name="Speedups"></a>
<div class="header">
<p>
Previous: <a href="#Ignoring-Changes" accesskey="p" rel="prev">Ignoring Changes</a>, Up: <a href="#Shortcomings" accesskey="u" rel="up">Shortcomings</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="Improving-Performance"></a>
<h4 class="subsection">18.1.7 Improving Performance</h4>

<p>When comparing two large directory structures, one of which was
originally copied from the other with time stamps preserved (e.g.,
with &lsquo;<samp>cp -pR</samp>&rsquo;), it would greatly improve performance if an option
told <code>diff</code> to assume that two files with the same size and
time stamps have the same content.  See <a href="diff-Performance.html#diff-Performance">diff Performance</a>.
</p>
<hr>
<a name="Bugs"></a>
<div class="header">
<p>
Previous: <a href="#Shortcomings" accesskey="p" rel="prev">Shortcomings</a>, Up: <a href="#Projects" accesskey="u" rel="up">Projects</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="Reporting-Bugs"></a>
<h3 class="section">18.2 Reporting Bugs</h3>
<a name="index-bug-reports"></a>
<a name="index-reporting-bugs"></a>

<p>If you think you have found a bug in <acronym>GNU</acronym> <code>cmp</code>,
<code>diff</code>, <code>diff3</code>, or <code>sdiff</code>, please report it
by electronic mail to the
<a href="http://mail.gnu.org/mailman/listinfo/bug-diffutils">GNU utilities
bug report mailing list</a> <a href="mailto:bug-diffutils@gnu.org">bug-diffutils@gnu.org</a>.  Please send
bug reports for <acronym>GNU</acronym> <code>patch</code> to
<a href="mailto:bug-patch@gnu.org">bug-patch@gnu.org</a>.  Send as precise a description of the
problem as you can, including the output of the <samp>--version</samp>
option and sample input files that produce the bug, if applicable.  If
you have a nontrivial fix for the bug, please send it as well.  If you
have a patch, please send it too.  It may simplify the maintainer&rsquo;s
job if the patch is relative to a recent test release, which you can
find in the directory <a href="ftp://alpha.gnu.org/gnu/diffutils/">ftp://alpha.gnu.org/gnu/diffutils/</a>.
</p>
<hr>
<div class="header">
<p>
Previous: <a href="#Shortcomings" accesskey="p" rel="prev">Shortcomings</a>, Up: <a href="#Projects" accesskey="u" rel="up">Projects</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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