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» Finding duplicated code with CPD
<a
target="_blank"
href="https://github.com/pmd/pmd/blob/master/docs/pages/pmd/userdocs/cpd/cpd.md"
class="pull-right"
role="button"
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<h1 class="post-title-main">Finding duplicated code with CPD</h1>
</div>
<div class="post-content" data-github-edit-url="https://github.com/pmd/pmd/blob/master/docs/pages/pmd/userdocs/cpd/cpd.md">
<div class="summary">Learn how to use CPD, the copy-paste detector shipped with PMD.</div>
<div id="inline-toc"><!-- empty, move TOC here when screen size too small --></div>
<h2 id="overview">Overview</h2>
<p>Duplicate code can be hard to find, especially in a large project.
But PMD’s <strong>Copy/Paste Detector (CPD)</strong> can find it for you!</p>
<p>CPD works with Java, JSP, C/C++, C#, Go, Kotlin, Ruby, Swift and <a href="#supported-languages">many more languages</a>.
It can be used via <a href="#cli-usage">command-line</a>, or via an <a href="#ant-task">Ant task</a>.
It can also be run with Maven by using the <code class="language-plaintext highlighter-rouge">cpd-check</code> goal on the <a href="pmd_userdocs_tools_maven.html">Maven PMD Plugin</a>.</p>
<p>Your own language is missing?
See how to add it <a href="pmd_devdocs_major_adding_new_cpd_language.html">here</a>.</p>
<h3 id="why-should-you-care-about-duplicates">Why should you care about duplicates?</h3>
<p>It’s certainly important to know where to get CPD, and how to call it, but it’s worth stepping back for a moment and asking yourself why you should care about this, being the occurrence of duplicate code blocks.</p>
<p>Assuming duplicated blocks of code are supposed to do the same thing, any refactoring, even simple, must be duplicated too – which is unrewarding grunt work, and puts pressure on the developer to find every place in which to perform the refactoring. Automated tools like CPD can help with that to some extent.</p>
<p>However, failure to keep the code in sync may mean automated tools will no longer recognise these blocks as duplicates. This means the task of finding duplicates to keep them in sync when doing subsequent refactorings can no longer be entrusted to an automated tool – adding more burden on the maintainer. Segments of code initially supposed to do the same thing may grow apart undetected upon further refactoring.</p>
<p>Now, if the code may never change in the future, then this is not a problem.</p>
<p>Otherwise, the most viable solution is to not duplicate. If the duplicates are already there, then they should be refactored out. We thus advise developers to use CPD to <strong>help remove duplicates</strong>, not to help keep duplicates in sync.</p>
<h3 id="refactoring-duplicates">Refactoring duplicates</h3>
<p>Once you have located some duplicates, several refactoring strategies may apply depending of the scope and extent of the duplication. Here’s a quick summary:</p>
<ul>
<li>If the duplication is local to a method or single class:
<ul>
<li>Extract a local variable if the duplicated logic is not prohibitively long</li>
<li>Extract the duplicated logic into a private method</li>
</ul>
</li>
<li>If the duplication occurs in siblings within a class hierarchy:
<ul>
<li>Extract a method and pull it up in the class hierarchy, along with common fields</li>
<li>Use the <a href="https://sourcemaking.com/design_patterns/template_method">Template Method</a> design pattern</li>
</ul>
</li>
<li>If the duplication occurs consistently in unrelated hierarchies:
<ul>
<li>Introduce a common ancestor to those class hierarchies</li>
</ul>
</li>
</ul>
<p>Novice as much as advanced readers may want to <a href="https://refactoring.guru/smells/duplicate-code">read on on Refactoring Guru</a> for more in-depth strategies, use cases and explanations.</p>
<h2 id="cli-usage">CLI Usage</h2>
<h3 id="cli-options-reference">CLI options reference</h3>
<table>
<tr>
<th>Option</th>
<th>Description</th>
<th>Default</th>
<th>Applies to</th>
</tr>
<!-- Row of the CLI reference table, describing an option -->
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<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="-minimum-tokens"><code>--minimum-tokens</code></a></td>
<td><span class="label label-primary">Required</span> The minimum token length which should be reported as a duplicate.</td>
<td><code></code></td>
<td></td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="-files"><code>--files</code></a></td>
<td><span class="label label-primary">Required</span> List of files and directories to process</td>
<td><code></code></td>
<td></td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="-file-list"><code>--file-list</code></a></td>
<td>Path to file containing a comma delimited list of files to analyze. If this is given, then you don't need to provide <code>--files</code>.</td>
<td><code></code></td>
<td></td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="-language"><code>--language</code></a></td>
<td>Sources code language.</td>
<td><code>java</code></td>
<td></td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="-debug"><code>--debug</code><br /><code>--verbose</code></a></td>
<td>Debug mode. Prints more log output.</td>
<td><code></code></td>
<td></td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="-encoding"><code>--encoding</code></a></td>
<td>Character encoding to use when processing files. If not specified, CPD uses the system default encoding.</td>
<td><code></code></td>
<td></td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="-skip-duplicate-files"><code>--skip-duplicate-files</code></a></td>
<td>Ignore multiple copies of files of the same name and length in comparison.</td>
<td><code>false</code></td>
<td></td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="-exclude"><code>--exclude</code></a></td>
<td>Files to be excluded from CPD check</td>
<td><code></code></td>
<td></td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="-non-recursive"><code>--non-recursive</code></a></td>
<td>Don't scan subdirectories</td>
<td><code>false</code></td>
<td></td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="-skip-lexical-errors"><code>--skip-lexical-errors</code></a></td>
<td>Skip files which can't be tokenized due to invalid characters instead of aborting CPD</td>
<td><code>false</code></td>
<td></td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="-format"><code>--format</code></a></td>
<td>Report format.</td>
<td><code>text</code></td>
<td></td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="-fail-on-violation"><code>--fail-on-violation&nbsp;&lt;bool&gt;</code></a></td>
<td>By default CPD exits with status 4 if code duplications are found.
Disable this option with <code>--fail-on-violation false</code> to exit with 0 instead and just write the report.</td>
<td><code>true</code></td>
<td></td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="-ignore-literals"><code>--ignore-literals</code></a></td>
<td>Ignore number values and string contents when comparing text</td>
<td><code>false</code></td>
<td>Java</td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="-ignore-identifiers"><code>--ignore-identifiers</code></a></td>
<td>Ignore constant and variable names when comparing text</td>
<td><code>false</code></td>
<td>Java</td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="-ignore-annotations"><code>--ignore-annotations</code></a></td>
<td>Ignore language annotations (Java) or attributes (C#) when comparing text</td>
<td><code>false</code></td>
<td>C#, Java</td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="-ignore-literal-sequences"><code>--ignore-literal-sequences</code></a></td>
<td>Ignore sequences of literals (common e.g. in list initializers)</td>
<td><code>false</code></td>
<td>C#, C++, Lua</td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="-ignore-usings"><code>--ignore-usings</code></a></td>
<td>Ignore <code>using</code> directives in C# when comparing text</td>
<td><code>false</code></td>
<td>C#</td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="-no-skip-blocks"><code>--no-skip-blocks</code></a></td>
<td>Do not skip code blocks matched by <code>--skip-blocks-pattern</code></td>
<td><code>false</code></td>
<td>C++</td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="-skip-blocks-pattern"><code>--skip-blocks-pattern</code></a></td>
<td>Pattern to find the blocks to skip. It is a string property and contains of two parts,
separated by <code>|</code>. The first part is the start pattern, the second part is the ending pattern.</td>
<td><code>#if&nbsp;0|#endif</code></td>
<td>C++</td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="-uri"><code>--uri</code></a></td>
<td>URI to process</td>
<td><code></code></td>
<td>PLSQL</td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="-help"><code>--help</code><br /><code>-h</code></a></td>
<td>Print help text</td>
<td><code>false</code></td>
<td></td>
</tr>
</table>
<h3 id="examples">Examples</h3>
<p><em>Note:</em> The following example use the Linux start script. For Windows, just replace “./run.sh cpd” by “cpd.bat”.</p>
<p>Minimum required options: Just give it the minimum duplicate size and the source directory:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>$ ./run.sh cpd --minimum-tokens 100 --files /usr/local/java/src/java
</code></pre></div></div>
<p>You can also specify the language:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>$ ./run.sh cpd --minimum-tokens 100 --files /path/to/c/source --language cpp
</code></pre></div></div>
<p>You may wish to check sources that are stored in different directories:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>$ ./run.sh cpd --minimum-tokens 100 --files /path/to/other/source --files /path/to/other/source --files /path/to/other/source --language fortran
</code></pre></div></div>
<p><em>There should be no limit to the number of ‘–files’, you may add… But if you stumble one, please tell us !</em></p>
<p>And if you’re checking a C source tree with duplicate files in different architecture directories
you can skip those using –skip-duplicate-files:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>$ ./run.sh cpd --minimum-tokens 100 --files /path/to/c/source --language cpp --skip-duplicate-files
</code></pre></div></div>
<p>You can also specify the encoding to use when parsing files:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>$ ./run.sh cpd --minimum-tokens 100 --files /usr/local/java/src/java --encoding utf-16le
</code></pre></div></div>
<p>You can also specify a report format - here we’re using the XML report:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>$ ./run.sh cpd --minimum-tokens 100 --files /usr/local/java/src/java --format xml
</code></pre></div></div>
<p>The default format is a text report, and there’s also a <code class="language-plaintext highlighter-rouge">csv</code> report.</p>
<p>Note that CPD is pretty memory-hungry; you may need to give Java more memory to run it, like this:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>$ export PMD_JAVA_OPTS=-Xmx512m
$ ./run.sh cpd --minimum-tokens 100 --files /usr/local/java/src/java
</code></pre></div></div>
<p>In order to change the heap size under Windows, you’ll need to edit the batch file <code class="language-plaintext highlighter-rouge">cpd.bat</code> or
set the environment variable <code class="language-plaintext highlighter-rouge">PMD_JAVA_OPTS</code> prior to starting CPD:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>C:\ &gt; cd C:\pmd-bin-6.50.0-SNAPSHOT\bin
C:\...\bin &gt; set PMD_JAVA_OPTS=-Xmx512m
C:\...\bin &gt; .\cpd.bat --minimum-tokens 100 --files c:\temp\src
</code></pre></div></div>
<p>If you specify a source directory but don’t want to scan the sub-directories, you can use the non-recursive option:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>$ ./run.sh cpd --minimum-tokens 100 --non-recursive --files /usr/local/java/src/java
</code></pre></div></div>
<h3 id="exit-status">Exit status</h3>
<p>Please note that if CPD detects duplicated source code, it will exit with status 4 (since 5.0).
This behavior has been introduced to ease CPD integration into scripts or hooks, such as SVN hooks.</p>
<table>
<tr><td>0</td><td>Everything is fine, no code duplications found</td></tr>
<tr><td>1</td><td>Couldn't understand command line parameters or CPD exited with an exception</td></tr>
<tr><td>4</td><td>At least one code duplication has been detected unless '--fail-on-violation false' is used.</td></tr>
</table>
<h2 id="supported-languages">Supported Languages</h2>
<ul>
<li>C#</li>
<li>C/C++</li>
<li>Dart</li>
<li>EcmaScript (JavaScript)</li>
<li>Fortran</li>
<li>Go</li>
<li>Groovy</li>
<li>Java</li>
<li>Jsp</li>
<li>Kotlin</li>
<li>Lua</li>
<li>Matlab</li>
<li>Modelica</li>
<li>Objective-C</li>
<li>Perl</li>
<li>PHP</li>
<li>PL/SQL</li>
<li>Python</li>
<li>Ruby</li>
<li>Salesforce.com Apex</li>
<li>Scala</li>
<li>Swift</li>
<li>Visualforce</li>
<li>XML</li>
</ul>
<h2 id="available-report-formats">Available report formats</h2>
<ul>
<li>text : Default format</li>
<li>xml</li>
<li>csv</li>
<li>csv_with_linecount_per_file</li>
<li>vs</li>
</ul>
<p>For details, see <a href="pmd_userdocs_cpd_report_formats.html">CPD Report Formats</a>.</p>
<h2 id="ant-task">Ant task</h2>
<p>Andy Glover wrote an Ant task for CPD; here’s how to use it:</p>
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt">&lt;target</span> <span class="na">name=</span><span class="s">"cpd"</span><span class="nt">&gt;</span>
<span class="nt">&lt;taskdef</span> <span class="na">name=</span><span class="s">"cpd"</span> <span class="na">classname=</span><span class="s">"net.sourceforge.pmd.cpd.CPDTask"</span> <span class="nt">/&gt;</span>
<span class="nt">&lt;cpd</span> <span class="na">minimumTokenCount=</span><span class="s">"100"</span> <span class="na">outputFile=</span><span class="s">"/home/tom/cpd.txt"</span><span class="nt">&gt;</span>
<span class="nt">&lt;fileset</span> <span class="na">dir=</span><span class="s">"/home/tom/tmp/ant"</span><span class="nt">&gt;</span>
<span class="nt">&lt;include</span> <span class="na">name=</span><span class="s">"**/*.java"</span><span class="nt">/&gt;</span>
<span class="nt">&lt;/fileset&gt;</span>
<span class="nt">&lt;/cpd&gt;</span>
<span class="nt">&lt;/target&gt;</span>
</code></pre></div></div>
<!-- TODO avoid duplicating the descriptions! -->
<h3 id="attribute-reference">Attribute reference</h3>
<table>
<tr>
<th>Attribute</th>
<th>Description</th>
<th>Default</th>
<th>Applies to</th>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="minimumtokencount"><code>minimumtokencount</code></a></td>
<td><span class="label label-primary">Required</span> A positive integer indicating the minimum duplicate size.</td>
<td><code></code></td>
<td></td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="encoding"><code>encoding</code></a></td>
<td>The character set encoding (e.g., UTF-8) to use when reading the source code files, but also when
producing the report. A piece of warning, even if you set properly the encoding value,
let's say to UTF-8, but you are running CPD encoded with CP1252, you may end up with not UTF-8 file.
Indeed, CPD copy piece of source code in its report directly, therefore, the source files
keep their encoding.<br />
If not specified, CPD uses the system default encoding.</td>
<td><code></code></td>
<td></td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="format"><code>format</code></a></td>
<td>The format of the report (e.g. <code>csv</code>, <code>text</code>, <code>xml</code>).</td>
<td><code>text</code></td>
<td></td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="ignoreLiterals"><code>ignoreLiterals</code></a></td>
<td>if <code>true</code>, CPD ignores literal value differences when evaluating a duplicate
block. This means that <code>foo=42;</code> and <code>foo=43;</code> will be seen as equivalent. You may want
to run PMD with this option off to start with and then switch it on to see what it turns up.</td>
<td><code>false</code></td>
<td>Java</td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="ignoreIdentifiers"><code>ignoreIdentifiers</code></a></td>
<td>Similar to <code>ignoreLiterals</code> but for identifiers; i.e., variable names, methods names, and so forth.</td>
<td><code>false</code></td>
<td>Java</td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="ignoreAnnotations"><code>ignoreAnnotations</code></a></td>
<td>Ignore annotations. More and more modern frameworks use annotations on classes and methods,
which can be very redundant and trigger CPD matches. With J2EE (CDI, Transaction Handling, etc)
and Spring (everything) annotations become very redundant. Often classes or methods have the
same 5-6 lines of annotations. This causes false positives.</td>
<td><code>false</code></td>
<td>Java</td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="ignoreUsings"><code>ignoreUsings</code></a></td>
<td>Ignore using directives in C#.</td>
<td><code>false</code></td>
<td>C#</td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="skipDuplicateFiles"><code>skipDuplicateFiles</code></a></td>
<td>Ignore multiple copies of files of the same name and length in comparison.</td>
<td><code>false</code></td>
<td></td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="skipLexicalErrors"><code>skipLexicalErrors</code></a></td>
<td>Skip files which can't be tokenized due to invalid characters instead of aborting CPD.</td>
<td><code>false</code></td>
<td></td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="skipBlocks"><code>skipBlocks</code></a></td>
<td>Enables or disabled skipping of blocks like a pre-processor. See also option skipBlocksPattern.</td>
<td><code>true</code></td>
<td>C++</td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="skipBlocksPattern"><code>skipBlocksPattern</code></a></td>
<td>Configures the pattern, to find the blocks to skip. It is a string property and contains of two parts,
separated by <code>|</code>. The first part is the start pattern, the second part is the ending pattern.</td>
<td><code>#if&nbsp;0|#endif</code></td>
<td>C++</td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="language"><code>language</code></a></td>
<td>Flag to select the appropriate language (e.g. <code>c</code>, <code>cpp</code>, <code>cs</code>, <code>java</code>, <code>jsp</code>, <code>php</code>, <code>ruby</code>, <code>fortran</code>
<code>ecmascript</code>, and <code>plsql</code>).</td>
<td><code>java</code></td>
<td></td>
</tr>
<!-- Row of the CLI reference table, describing an option -->
<!-- Rows can be linked to the name of the option (without leading dash) -->
<!-- Argument summary: -->
<!-- options: comma separated list of aliases for the option.-->
<!-- option_arg: optional name for the argument of the option, eg 'arg', will be formatted eg to '<arg>'-->
<!-- description: description, you can use "some" inline markdown -->
<!-- required: whether the option is required, if specified, whatever the value, it's considered required -->
<!-- languages: languages to which the option applies -->
<!-- default: default value -->
<!-- fragment id in the page -->
<tr>
<td><a style="pointer-events: none; cursor: default;" name="outputfile"><code>outputfile</code></a></td>
<td>The destination file for the report. If not specified the console will be used instead.</td>
<td><code></code></td>
<td></td>
</tr>
</table>
<p>Also, you can get verbose output from this task by running ant with the <code class="language-plaintext highlighter-rouge">-v</code> flag; i.e.:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>ant -v -f mybuildfile.xml cpd
</code></pre></div></div>
<p>Also, you can get an HTML report from CPD by using the XSLT script in pmd/etc/xslt/cpdhtml.xslt. Just run
the CPD task as usual and right after it invoke the Ant XSLT script like this:</p>
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt">&lt;xslt</span> <span class="na">in=</span><span class="s">"cpd.xml"</span> <span class="na">style=</span><span class="s">"etc/xslt/cpdhtml.xslt"</span> <span class="na">out=</span><span class="s">"cpd.html"</span> <span class="nt">/&gt;</span>
</code></pre></div></div>
<h2 id="gui">GUI</h2>
<p>CPD also comes with a simple GUI. You can start it via some scripts in the <code class="language-plaintext highlighter-rouge">bin</code> folder:</p>
<p>For Windows:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>cpdgui.bat
</code></pre></div></div>
<p>For Linux:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>./run.sh cpdgui
</code></pre></div></div>
<p>Here’s a screenshot of CPD after running on the JDK 8 java.lang package:</p>
<figure><img class="docimage" src="images/userdocs/screenshot_cpd.png" alt="CPD Screenshot after running on the JDK 8 java.lang package" /></figure>
<h2 id="suppression">Suppression</h2>
<p>Arbitrary blocks of code can be ignored through comments on <strong>Java</strong>, <strong>C/C++</strong>, <strong>Dart</strong>, <strong>Go</strong>, <strong>Javascript</strong>,
<strong>Kotlin</strong>, <strong>Lua</strong>, <strong>Matlab</strong>, <strong>Objective-C</strong>, <strong>PL/SQL</strong>, <strong>Python</strong>, <strong>Scala</strong>, <strong>Swift</strong> and <strong>C#</strong> by including the keywords <code class="language-plaintext highlighter-rouge">CPD-OFF</code> and <code class="language-plaintext highlighter-rouge">CPD-ON</code>.</p>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="nc">Object</span> <span class="nf">someParameterizedFactoryMethod</span><span class="o">(</span><span class="kt">int</span> <span class="n">x</span><span class="o">)</span> <span class="kd">throws</span> <span class="nc">Exception</span> <span class="o">{</span>
<span class="c1">// some unignored code</span>
<span class="c1">// tell cpd to start ignoring code - CPD-OFF</span>
<span class="c1">// mission critical code, manually loop unroll</span>
<span class="n">goDoSomethingAwesome</span><span class="o">(</span><span class="n">x</span> <span class="o">+</span> <span class="n">x</span> <span class="o">/</span> <span class="mi">2</span><span class="o">);</span>
<span class="n">goDoSomethingAwesome</span><span class="o">(</span><span class="n">x</span> <span class="o">+</span> <span class="n">x</span> <span class="o">/</span> <span class="mi">2</span><span class="o">);</span>
<span class="n">goDoSomethingAwesome</span><span class="o">(</span><span class="n">x</span> <span class="o">+</span> <span class="n">x</span> <span class="o">/</span> <span class="mi">2</span><span class="o">);</span>
<span class="n">goDoSomethingAwesome</span><span class="o">(</span><span class="n">x</span> <span class="o">+</span> <span class="n">x</span> <span class="o">/</span> <span class="mi">2</span><span class="o">);</span>
<span class="n">goDoSomethingAwesome</span><span class="o">(</span><span class="n">x</span> <span class="o">+</span> <span class="n">x</span> <span class="o">/</span> <span class="mi">2</span><span class="o">);</span>
<span class="n">goDoSomethingAwesome</span><span class="o">(</span><span class="n">x</span> <span class="o">+</span> <span class="n">x</span> <span class="o">/</span> <span class="mi">2</span><span class="o">);</span>
<span class="c1">// resume CPD analysis - CPD-ON</span>
<span class="c1">// further code will *not* be ignored</span>
<span class="o">}</span>
</code></pre></div></div>
<p>Additionally, <strong>Java</strong> allows to toggle suppression by adding the annotations
<strong><code class="language-plaintext highlighter-rouge">@SuppressWarnings("CPD-START")</code></strong> and <strong><code class="language-plaintext highlighter-rouge">@SuppressWarnings("CPD-END")</code></strong>
all code within will be ignored by CPD.</p>
<p>This approach however, is limited to the locations were <code class="language-plaintext highlighter-rouge">@SuppressWarnings</code> is accepted.
It’s legacy and the new comment’s based approach should be favored.</p>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="c1">//enable suppression</span>
<span class="nd">@SuppressWarnings</span><span class="o">(</span><span class="s">"CPD-START"</span><span class="o">)</span>
<span class="kd">public</span> <span class="nc">Object</span> <span class="nf">someParameterizedFactoryMethod</span><span class="o">(</span><span class="kt">int</span> <span class="n">x</span><span class="o">)</span> <span class="kd">throws</span> <span class="nc">Exception</span> <span class="o">{</span>
<span class="c1">// any code here will be ignored for the duplication detection</span>
<span class="o">}</span>
<span class="c1">//disable suppression</span>
<span class="nd">@SuppressWarnings</span><span class="o">(</span><span class="err">"</span><span class="no">CPD</span><span class="o">-</span><span class="no">END</span><span class="o">)</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">nextMethod</span><span class="o">()</span> <span class="o">{</span>
<span class="o">}</span>
</code></pre></div></div>
<p>Other languages currently have no support to suppress CPD reports. In the future,
the comment based approach will be extended to those of them that can support it.</p>
<h2 id="credits">Credits</h2>
<p>CPD has been through three major incarnations:</p>
<ul>
<li>
<p>First we wrote it using a variant of Michael Wise’s Greedy String Tiling algorithm (our variant is described
<a href="http://www.onjava.com/pub/a/onjava/2003/03/12/pmd_cpd.html">here</a>).</p>
</li>
<li>
<p>Then it was completely rewritten by Brian Ewins using the
<a href="http://dogma.net/markn/articles/bwt/bwt.htm">Burrows-Wheeler transform</a>.</p>
</li>
<li>
<p>Finally, it was rewritten by Steve Hawkins to use the
<a href="http://www.nist.gov/dads/HTML/karpRabin.html">Karp-Rabin</a> string matching algorithm.</p>
</li>
</ul>
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