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<h2 id="replaceregexp">ReplaceRegExp</h2>
<h3>Description</h3>
<p>ReplaceRegExp is a directory based task for replacing the
occurrence of a given regular expression with a substitution pattern
in a selected file or set of files.</p>

<p>The output file is only written if it differs from the existing
file.  This prevents spurious rebuilds based on unchanged files which
have been regenerated by this task.</p>

<p>Similar to <a href="../Types/mapper.html#regexp-mapper">regexp
type mappers</a> this task needs a supporting regular expression
library and an implementation of
<code>org.apache.tools.ant.util.regexp.Regexp</code>.
See details in the documentation of the <a href="../Types/regexp.html#implementation">Regexp Type</a>.</p>

<h3>Parameters</h3>
<table>
  <tr>
    <td valign="top"><b>Attribute</b></td>
    <td valign="top"><b>Description</b></td>
    <td align="center" valign="top"><b>Required</b></td>
  </tr>
  <tr>
    <td valign="top">file</td>
    <td valign="top">file for which the regular expression should be replaced.</td>
    <td align="center">Yes if no nested <code>&lt;fileset&gt;</code> is used</td>
  </tr>
  <tr>
    <td valign="top">match</td>
    <td valign="top">The regular expression pattern to match in the file(s)</td>
    <td align="center">Yes, if no nested <code>&lt;regexp&gt;</code> is used</td>
  </tr>
  <tr>
    <td valign="top">replace</td>
    <td valign="top">The substitution pattern to place in the file(s) in place
                     of the regular expression.</td>
    <td align="center">Yes, if no nested <code>&lt;substitution&gt;</code> is used</td>
  </tr>
  <tr>
    <td valign="top">flags</td>
    <td valign="top">The flags to use when matching the regular expression.  For more
                     information, consult the Perl5 syntax<br>
                     g : Global replacement.  Replace all occurrences found<br>
                     i : Case Insensitive.  Do not consider case in the match<br>
                     m : Multiline.  Treat the string as multiple lines of input, using "^" and "$" as the start or end of any line, respectively, rather than start or end of string.<br>
                     s : Singleline.  Treat the string as a single line of input, using "." to match any character, including a newline, which normally, it would not match.<br>
    </td>
    <td valign="top" align="center">No</td>
  </tr>
  <tr>
    <td valign="top">byline</td>
    <td valign="top">Process the file(s) one line at a time, executing the replacement
                     on one line at a time (<i>true/false</i>).  This is useful if you
                     want to only replace the first occurrence of a regular expression on
                     each line, which is not easy to do when processing the file as a whole.
                     Defaults to <i>false</i>.</td>
    <td valign="top" align="center">No</td>
  </tr>
  <tr>
    <td valign="top">encoding</td>
    <td valign="top">The encoding of the file. <em>since Apache Ant 1.6</em></td>
    <td align="center">No - defaults to default JVM encoding</td>
  </tr>
  <tr>
    <td valign="top">preserveLastModified</td>
    <td valign="top">Keep the file timestamp(s) even if the file(s)
      is(are) modified.  <em>since Ant 1.8.0</em>.</td>
    <td valign="top" align="center">No, defaults to false</td>
  </tr>
</table>
<h3>Examples</h3>
<pre>
&lt;replaceregexp file=&quot;${src}/build.properties&quot;
               match=&quot;OldProperty=(.*)&quot;
               replace=&quot;NewProperty=\1&quot;
               byline=&quot;true&quot;
/&gt;
</pre>
<p>replaces occurrences of the property name &quot;OldProperty&quot;
 with &quot;NewProperty&quot; in a properties file, preserving the existing
value, in the file <code>${src}/build.properties</code></p>

<h3>Parameters specified as nested elements</h3>
<p>This task supports a nested <a href="../Types/fileset.html">FileSet</a>
   element.</p>
<p><em>Since Ant 1.8.0</em>, this task supports any filesystem
  based <a href="../Types/resources.html#collection">resource
    collections</a> as nested elements.</p>
<p>This task supports a nested <i><a href="../Types/regexp.html">Regexp</a></i> element to specify
   the regular expression.  You can use this element to refer to a previously
   defined regular expression datatype instance.</p>
<blockquote>
     &lt;regexp id="id" pattern="alpha(.+)beta"/&gt;<br>
     &lt;regexp refid="id"/&gt;
</blockquote>
<p>This task supports a nested <i>Substitution</i> element to specify
   the substitution pattern.  You can use this element to refer to a previously
   defined substitution pattern datatype instance.</p>
<blockquote>
     &lt;substitution id="id" expression="beta\1alpha"/&gt;<br>
     &lt;substitution refid="id"/&gt;
</blockquote>


<h3>Examples</h3>

<blockquote>
  <pre>
&lt;replaceregexp byline=&quot;true&quot;&gt;
  &lt;regexp pattern=&quot;OldProperty=(.*)&quot;/&gt;
  &lt;substitution expression=&quot;NewProperty=\1&quot;/&gt;
  &lt;fileset dir=&quot;.&quot;&gt;
    &lt;include name=&quot;*.properties&quot;/&gt;
  &lt;/fileset&gt;
&lt;/replaceregexp&gt;
</pre></blockquote>
<p>replaces occurrences of the property name &quot;OldProperty&quot;
 with &quot;NewProperty&quot; in a properties file, preserving the existing
value, in all files ending in <code>.properties</code> in the current directory</p>

<br>
<blockquote>
<pre>&lt;replaceregexp match="\s+" replace=" " flags="g" byline="true"&gt;
    &lt;fileset dir="${html.dir}" includes="**/*.html"/&gt;
&lt;/replaceregexp&gt;
</pre></blockquote>
<p>replaces all whitespaces (blanks, tabs, etc) by one blank remaining the
line separator. So with input</p>
<blockquote>
<pre>
&lt;html&gt;    &lt;body&gt;
&lt;&lt;TAB&gt;&gt;&lt;h1&gt;    T E S T   &lt;/h1&gt;  &lt;&lt;TAB&gt;&gt;
&lt;&lt;TAB&gt;&gt; &lt;/body&gt;&lt;/html&gt;
</pre></blockquote>
<p>would converted to</p>
<blockquote>
<pre>
&lt;html&gt; &lt;body&gt;
 &lt;h1&gt; T E S T &lt;/h1&gt; &lt;/body&gt;&lt;/html&gt;
</pre>
</blockquote>

<br><!-- small distance from code of the previous example -->
<blockquote>
<pre>&lt;replaceregexp match="\\n" replace="${line.separator}" flags="g" byline="true"&gt;
    &lt;fileset dir="${dir}"/&gt;
&lt;/replaceregexp&gt;
</pre></blockquote>
<p>replaces all <tt>\n</tt> markers (beware the quoting of the backslash) by a line break.
So with input</p>
<blockquote>
<pre>
one\ntwo\nthree
</pre></blockquote>
<p>would converted to</p>
<blockquote>
<pre>
one
two
three
</pre>
</blockquote>
<p>Beware that inserting line breaks could break file syntax. For example in xml:</p>
<blockquote>
<pre>
&lt;root&gt;
  &lt;text&gt;line breaks \n should work in text&lt;/text&gt;
  &lt;attribute value=&quot;but breaks \n attributes&quot; /&gt;
&lt;/root&gt;
</pre>
</blockquote>

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