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unix 下的C开发手册,还用详细的例程。

into
<i>file2</i>.
The line numbers before the action letters pertain to
<i>file1</i>;
those after pertain to
<i>file2</i>.
Thus, by exchanging
a
for
d
and
reading the line in reverse order, one can also determine how to convert
<i>file2</i>
into
<i>file1</i>.
As in
<i><a href="ed.html">ed</a></i>,
identical pairs (where <i>num1</i><b>&nbsp;=&nbsp;</b><i>num2</i>)
are abbreviated as a single number.
<p>
Following each of these lines,
<i>diff</i>
will write to standard output
all lines affected in the first file using the format:
<p>
<code>
<tt>"&lt;<img src="../images/delta.gif" border=0>%s"</tt>, &lt;<i>line</i>&gt;
</code>
<p>
and all lines affected in the second file using the format:
<p>
<code>
<tt>"&gt;<img src="../images/delta.gif" border=0>%s"</tt>, &lt;<i>line</i>&gt;
</code>
<p>
If there are lines affected in both
<i>file1</i>
and
<i>file2</i>
(as with the
<b>c</b>
subcommand), the changes are separated with a
line consisting of three hyphens:
<pre>
<code>
"---\n"
</code>
</pre>
<h5><a name = "tag_001_014_424_003">&nbsp;</a>Diff -e Output Format</h5>
With the
<b>-e</b>
option,
a script will be produced that will,
when provided as input to
<i><a href="ed.html">ed</a></i>,
along with an appended
<b>w</b>
(write) command, convert
<i>file1</i>
into
<i>file2</i>.
Only the
<b>a</b>
(append),
<b>c</b>
(change),
<b>d</b>
(delete),
<b>i</b>
(insert), and
<b>s</b>
(substitute) commands of
<i><a href="ed.html">ed</a></i>
will be used in this script.
Text lines, except those consisting of the single character period
(.),
will be output as they appear in the file.
<h5><a name = "tag_001_014_424_004">&nbsp;</a>Diff -f Output Format</h5>
With the
<b>-f</b>
option,
an alternative format of script will be produced.
It will be similar to that produced by
<b>-e</b>,
with the following differences:
<ol>
<p>
<li>
It will be expressed in reverse sequence;
the output of
<b>-e</b>
will order changes from the end of the file to the beginning;
the
<b>-f</b>
from beginning to end.
<p>
<li>
The command form
&lt;<i>lines</i>&gt;
&lt;<i>command-letter</i>&gt;
used by
<b>-e</b>
will be reversed.
For example,
10c
with
<b>-e</b>
would be
c10
with
<b>-f</b>.
<p>
<li>
The form used for ranges of line numbers will be
space-character-separated,
rather than comma-separated.
<p>
</ol>
<h5><a name = "tag_001_014_424_005">&nbsp;</a>Diff -c or -C Output Format</h5>
With the
<b>-c</b>
or
<b>-C</b>
option, the output format will consist of affected lines along with
surrounding lines of context.
The affected lines will show which
ones need to be deleted or changed in
<i>file1</i>,
and those
added from
<i>file2</i>.
With the
<b>-c</b>
option,
three lines of context,
if available, will be written before and
after the affected lines.
With the
<b>-C</b>
option, the user
can specify how many lines of context will be written.
The exact format follows.
<p>
The name and last modification time
of each file will be output in the following format:
<p><code>
<pre>
<tt>"*** %s %s\n"</tt>, <i>file1</i>,
&lt;<i>file1&nbsp;time&nbsp;stamp</i>&gt;
<tt>"--- %s %s\n"</tt>, <i>file2</i>,
&lt;<i>file2&nbsp;time&nbsp;stamp</i>&gt;
</code>
</pre>
and a string of 15 asterisks:
<pre>
<code>
"***************\n"
</code>
</pre>
<p>
Each
&lt;<i>file</i>&gt;
field will be the pathname of the corresponding file being compared.
The pathname written for standard input is unspecified.
<p>
In the POSIX locale, each
&lt;<i>timestamp</i>&gt;
field will be equivalent to the
output from the following command:
<pre>
<code>
date "+%a %b %e %T %Y"
</code>
</pre>
without the trailing
newline character,
executed at the time of last modification
of the corresponding file
(or the current time, if the file is standard input).
<p>
Then, the following output formats will be applied for every set of changes.
<p>
First, the range of lines in
<i>file1</i>
will be written in the following format:
<p><code>
<tt>"*** %d,%d ****\n"</tt>, &lt;<i>beginning&nbsp;line&nbsp;number</i>&gt;,
&lt;<i>ending&nbsp;line&nbsp;number</i>&gt;
</code>
<p>
Next, the affected lines along with lines of context (unaffected lines)
will be written.
Unaffected lines will be written in the following format:
<p><code>
<tt>"<img src="../images/delta.gif" border=0>%s"</tt>, &lt;<i>unaffected_line</i>&gt;
</code>
<p>
Deleted lines will be written as:
<p><code>
<tt>"-<img src="../images/delta.gif" border=0>2%s"</tt>, &lt;<i>deleted_line</i>&gt;
</code>
<p>
Changed lines will be written as:
<p><code>
<tt>"!<img src="../images/delta.gif" border=0>%s"</tt>, &lt;<i>changed_line</i>&gt;
</code>
<p>
Next, the range of lines in
<i>file2</i>
will be written in the following format:
<p><code>
<tt>"--- %d,%d ----\n"</tt>, &lt;<i>beginning line number</i>&gt;,
&lt;<i>ending line number</i>&gt;
</code>
<p>
Then, lines of context and changed lines will be written as described
in the previous formats.
Lines added from
<i>file2</i>
will be written in the following format:
<p><code>
<tt>"+<img src="../images/delta.gif" border=0>%s"</tt>, &lt;<i>added_line</i>&gt;
</code>
</blockquote><h4><a name = "tag_001_014_425">&nbsp;</a>STDERR</h4><blockquote>
Used only for diagnostic messages.
</blockquote><h4><a name = "tag_001_014_426">&nbsp;</a>OUTPUT FILES</h4><blockquote>
None.
</blockquote><h4><a name = "tag_001_014_427">&nbsp;</a>EXTENDED DESCRIPTION</h4><blockquote>
None.
</blockquote><h4><a name = "tag_001_014_428">&nbsp;</a>EXIT STATUS</h4><blockquote>
The following exit values are returned:
<dl compact>

<dt>0<dd>No differences were found.

<dt>1<dd>Differences were found.

<dt>&gt;1<dd>An error occurred.

</dl>
</blockquote><h4><a name = "tag_001_014_429">&nbsp;</a>CONSEQUENCES OF ERRORS</h4><blockquote>
Default.
</blockquote><h4><a name = "tag_001_014_430">&nbsp;</a>APPLICATION USAGE</h4><blockquote>
If lines at the end of a file are changed and other lines are added,
<i>diff</i>
output may show this as a delete and add, as a change, or as a change and
add;
<i>diff</i>
is not expected to know which happened and users should not
care about the difference in output as long as it clearly shows the
differences between the files.
</blockquote><h4><a name = "tag_001_014_431">&nbsp;</a>EXAMPLES</h4><blockquote>
If
<b>dir1</b>
is a directory containing a directory named
<b>x</b>,
<b>dir2</b>
is a directory containing a directory named
<b>x</b>,
<b>dir1/x</b>
and
<b>dir2/x</b>
both contain files named
<b>date.out</b>,
and
<b>dir2/x</b>
contains a file named
<b>y</b>,
the command:
<pre>
<code>
diff -r dir1 dir2
</code>
</pre>
could produce output similar to:
<pre>
<code>
Common subdirectories: dir1/x and dir2/x
Only in dir2/x: y
diff -r dir1/x/date.out dir2/x/date.out
1c1
&lt; Mon Jul  2 13:12:16 PDT 1990
---
&gt; Tue Jun 19 21:41:39 PDT 1990
</code>
</pre>
</blockquote><h4><a name = "tag_001_014_432">&nbsp;</a>FUTURE DIRECTIONS</h4><blockquote>
The IEEE PASC 1003.2 Interpretations Committee has forwarded concerns about 
parts of this interface definition to the IEEE PASC Shell and Utilities Working Group
which is identifying the corrections.
A future revision of this specification will align with
IEEE Std. 1003.2b when finalised.
</blockquote><h4><a name = "tag_001_014_433">&nbsp;</a>SEE ALSO</h4><blockquote>
<i><a href="cmp.html">cmp</a></i>,
<i><a href="comm.html">comm</a></i>,
<i><a href="dircmp.html">dircmp</a></i>,
<i><a href="ed.html">ed</a></i>.
<br>
</blockquote><hr size=2 noshade>
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