<?xml version="1.0" encoding="UTF-8"?>
<article id="Filters">
  <title>Using Filters<indexterm>
      <primary>filters</primary>

      <seealso>file filters</seealso>

      <seealso>file masks</seealso>

      <seealso>line filters</seealso>
    </indexterm></title>

  <para>When you compare files or folders, you can use filters to narrow the
  scope of the comparison. This can be useful when you want to simplify the
  comparison result by eliminating differences that you are not interested in.
  Filters are rules based on regular expressions. WinMerge uses the popular PCRE
  (Perl Compatible Regular Expressions) regular expression engine.<indexterm>
      <primary>regular expressions</primary>

      <secondary>supported engine</secondary>
    </indexterm><indexterm>
      <primary>PCRE regular expression engine</primary>
    </indexterm><indexterm>
      <primary>regexp</primary>

      <see>regular expressions</see>
    </indexterm></para>

  <para>The basic function of filtering is simple: evaluate each item that would
  normally be compared (a folder, file, or line within a file), and if the
  filter expression matches the target item, apply the filter. Depending on the
  type of filter, the item is either included or excluded in the
  comparison.</para>

  <para>There are different WinMerge filters for folder compare and file compare
  operations:</para>

  <variablelist>
    <varlistentry>
      <term>Folder comparison: File masks and file filters<indexterm>
          <primary>comparing folders</primary>

          <secondary>filtering</secondary>
        </indexterm></term>

      <listitem>
        <para>You can specify files to include in a folder comparison by using
        simple file masks, or, for more complex filtering, by applying multiple
        rules specified in a file filter. You cannot apply both a file mask and
        a file filter in the same operation.</para>

        <para>Files and folders that are filtered are hidden in the result by
        default, which is typically what you want. You can click <menuchoice>
            <guimenu>View</guimenu>

            <guimenuitem>Show Skipped Items</guimenuitem>
          </menuchoice> to unhide filtered items, but the Folder Compare window
        shows only minimal information about them. For example, you cannot tell
        whether a skipped file is a text file or binary.</para>
      </listitem>
    </varlistentry>

    <varlistentry>
      <term>File comparisons: Line filters<indexterm>
          <primary>comparing files</primary>

          <secondary>filtering</secondary>
        </indexterm></term>

      <listitem>
        <para>Line filters are applied only to file compare operations. They let
        you ignore single line differences.</para>
      </listitem>
    </varlistentry>
  </variablelist>

  <section id="Filters_Mask">
    <title>Using file masks<indexterm>
        <primary>file masks</primary>
      </indexterm><indexterm>
        <primary>filters</primary>

        <secondary>file masks</secondary>
      </indexterm><indexterm>
        <primary>filters</primary>

        <secondary>in folder comparisons</secondary>
      </indexterm></title>

    <para>You can use one or more <glossterm>file masks</glossterm> that specify
    file extensions to include in a folder comparison. All other files are
    omitted from your selection.</para>

    <section id="Filters_MaskApply">
      <title>Defining and applying file masks<indexterm>
          <primary>command line</primary>

          <secondary>applying file masks</secondary>
        </indexterm></title>

      <para>Define and apply a file mask at the time you launch your folder
      compare operation:</para>

      <itemizedlist>
        <listitem>
          <para>If you are using the Select Files or Folders dialog, after
          choosing the <guilabel>Left</guilabel> and <guilabel>Right</guilabel>
          folders, enter one or more file masks in the
          <guilabel>Filter</guilabel> field. The masks are applied when you
          start the folder compare operation.</para>
        </listitem>

        <listitem>
          <para>If you are using the WinMerge command line, use the
          <option>-f</option> flag to specify file masks (see the example in the
          next section).</para>
        </listitem>
      </itemizedlist>

      <para>Remember, you cannot specify both a file mask and a file filter in
      the field or command line.</para>
    </section>

    <section id="Filters_MaskSyntax">
      <title>File mask syntax and example<indexterm>
          <primary>rules</primary>

          <secondary>file masks</secondary>
        </indexterm><indexterm>
          <primary>filters</primary>

          <secondary>file masks</secondary>
        </indexterm><indexterm>
          <primary>regular expressions</primary>

          <secondary>in file masks</secondary>
        </indexterm></title>

      <para>Use this syntax for file masks:</para>

      <synopsis>*.[<replaceable>extension</replaceable>][<replaceable>delimiter</replaceable> *.<replaceable>extension</replaceable> ...]</synopsis>

      <para>Valid delimiters are spaces, commas, colons or semicolons.</para>

      <para>A mask with no extension ( <filename>*.</filename> ) selects files
      without any extension, such as
      <filename><filename>README</filename></filename>.</para>

      <example>
        <title>File mask</title>

        <para>In this command-line example, the folder compare operation
        includes only files with <filename>xml</filename> or
        <filename>txt</filename> extensions. All other files are omitted:</para>

        <para><userinput>WinMergeU c:\project\docs c:\temp /f
        *.xml;*.txt</userinput></para>
      </example>
    </section>
  </section>

  <section id="Filters_FileFilter">
    <title>Using file filters<indexterm>
        <primary>filters</primary>

        <secondary>file filters</secondary>
      </indexterm><indexterm>
        <primary>filters</primary>

        <secondary>in folder comparisons</secondary>
      </indexterm></title>

    <para><glossterm>File filters</glossterm> are text files with an extension
    of <filename>flt</filename>. They enable you to apply multiple filtering
    rules to a folder comparison. Unlike file masks, file filters can either
    include or exclude matches.</para>

    <para><indexterm>
        <primary>file filters</primary>

        <secondary>template</secondary>
      </indexterm>WinMerge installs a number of predefined file filters. If
    these file filters do not provide the filtering you need, you can create
    your own. To make that task easier, WinMerge also provides a template file
    named <filename>FileFilter.tmpl</filename>. This section describes how to
    apply file filters to comparisons, and documents the file filter syntax.
    <xref linkend="Filters_dlg" /> describes how to add, edit, and manage
    filters.</para>

    <section id="Filters_FileFilterLoc">
      <title>File filter locations<indexterm>
          <primary>Filters folders</primary>

          <secondary>locations</secondary>
        </indexterm><indexterm>
          <primary>file filters</primary>

          <secondary>locations</secondary>
        </indexterm></title>

      <para>WinMerge automatically detects file filters in these
      locations:</para>

      <variablelist>
        <varlistentry>
          <term>Filters subfolder in the WinMerge installation folder</term>

          <listitem>
            <para>This is where the predefined file filters are installed. For
            example, <filename>C:\Program Files\WinMerge\Filters</filename>. You
            can create or copy filter files in this location to make them
            available to all users on your system.</para>

            <para>Before creating a new file filter, see if the predefined ones
            already contain what you need. If not, you might find useful rule
            examples in the existing files.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term>Default private filter folder</term>

          <listitem>
            <para>The location of this folder is defined in the System page of
            WinMerge options. By default, it is specified as a subfolder in your
            user profile folder (for example, <filename>My
            Documents\WinMerge\Filters</filename> in Windows XP). Filters that
            are created or copied here are normally visible only to you. If you
            create new file filters, you can copy them here to keep them
            private.</para>
          </listitem>
        </varlistentry>
      </variablelist>

      <para>Before you can apply file filters that exist in any other folder,
      you must first install them.</para>
    </section>

    <section id="Filters_FileFilterApply">
      <title>Applying file filters<indexterm>
          <primary>file filters</primary>

          <secondary>applying</secondary>
        </indexterm></title>

      <para>You can apply a file filter using any of these methods:</para>

      <itemizedlist>
        <listitem>
          <para>When you launch a folder compare from the Select Files or
          Folders dialog:</para>

          <orderedlist>
            <listitem>
              <para>After choosing the <guilabel>Left</guilabel> and
              <guilabel>Right</guilabel> folders, click
              <guibutton>Select</guibutton> next to the
              <guilabel>Filter</guilabel> field.</para>
            </listitem>

            <listitem>
              <para>In the Filters dialog, use the Filefilters tab to choose a
              file filter and load it in the <guilabel>Filter</guilabel>
              field.</para>

              <note>
                <para>If a file filter is currently enabled, the selected file
                filter is already loaded in the <guilabel>Filter</guilabel>
                field.</para>
              </note>
            </listitem>

            <listitem>
              <para>Proceed with the compare operation. The file in the
              <guilabel>Filter</guilabel> field is applied when you start the
              operation.</para>
            </listitem>
          </orderedlist>
        </listitem>

        <listitem>
          <para>To change file filtering after you have already launched a
          folder compare operation (for example, applying a different filter or
          disabling filtering):</para>

          <orderedlist>
            <listitem>
              <para>Click <menuchoice>
                  <guimenu>Tools</guimenu>

                  <guimenuitem>Filters</guimenuitem>
                </menuchoice>.</para>
            </listitem>

            <listitem>
              <para>In the Filters dialog, configure your new file filter
              setting, and click <guibutton>OK</guibutton>.</para>
            </listitem>

            <listitem>
              <para>The new filtering is not automatically applied when you
              close the Filters dialog: press <keycap>F5</keycap> to see the new
              results in the Folder Compare window.</para>
            </listitem>
          </orderedlist>
        </listitem>

        <listitem>
          <para><indexterm>
              <primary>command line</primary>

              <secondary>applying file filters</secondary>
            </indexterm>When you launch a folder compare from the WinMerge
          command line, use the <option>-f</option> flag to specify a file
          filter.</para>
        </listitem>
      </itemizedlist>

      <para>Remember, you cannot apply both a file mask and a file filter in the
      field or command line.</para>
    </section>

    <section id="Filters_FileFilterSyntax">
      <title>File filter syntax<indexterm>
          <primary>rules</primary>

          <secondary>file filter</secondary>
        </indexterm><indexterm>
          <primary>file filters</primary>

          <secondary>syntax</secondary>
        </indexterm></title>

      <para>This section describes the syntax of WinMerge file filters and
      provides guidelines for writing them.</para>

      <para>The comment delimiter is <code>##</code>. After a comment delimiter,
      all characters in a line are ignored. WinMerge ignores most whitespace
      characters in rules. However, a comment must always be preceded by one or
      more whitespace (space or tab) characters. To use <code>##</code> as
      characters in a rule, omit the whitespace prefix.</para>

      <para>The first two required lines of a file filter are:</para>

      <variablelist>
        <varlistentry>
          <term>name</term>

          <listitem>
            <para>The filter name that is listed in the Files dialog</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term>def</term>

          <listitem>
            <para>The type of filtering to be applied. Specify one of these
            values:</para>

            <variablelist>
              <varlistentry>
                <term>include</term>

                <listitem>
                  <para>Includes everything except items matching the specified
                  rule.</para>
                </listitem>
              </varlistentry>

              <varlistentry>
                <term>exclude</term>

                <listitem>
                  <para>Excludes everything except items matching the specified
                  rule.</para>

                  <para>When you choose the exclude method, you must also add a
                  <guilabel>d</guilabel> (directory) rule that specifies the
                  subfolders. It's usually a good idea to specify all
                  subfolders, like this:</para>

                  <screen>d: \\*$ ## Subfolders</screen>
                </listitem>
              </varlistentry>
            </variablelist>

            <tip>
              <para>Don't confuse these terms. Remember, in file filters, an
              <guilabel>include</guilabel> rule does not specify what to
              include, it specifies what <emphasis>not</emphasis> to include.
              Similarly, <guilabel>exclude</guilabel> does not specify what to
              exclude, it specifies what not to exclude.</para>
            </tip>
          </listitem>
        </varlistentry>
      </variablelist>

      <para>Next, your file should contain one or more filter rules. You can add
      as many rules as you like. There must be one rule per line, and each rule
      must be entirely on one line (no line breaks are allowed in a rule). Each
      rule consists of either an <guilabel>f:</guilabel> or a
      <guilabel>d:</guilabel> type designator, followed by a reqular expression,
      where:</para>

      <variablelist>
        <varlistentry>
          <term>f: <replaceable>regexp</replaceable></term>

          <listitem>
            <para>matches for files, or</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term>d: <replaceable>regexp</replaceable></term>

          <listitem>
            <para>matches for folders</para>
          </listitem>
        </varlistentry>
      </variablelist>

      <para>Among the many regexp special characters, the following are
      particularly important in file filter rules:<indexterm>
          <primary>regular expressions</primary>

          <secondary>special characters in filters</secondary>
        </indexterm><indexterm>
          <primary>regular expressions</primary>

          <secondary>in file filters</secondary>
        </indexterm></para>

      <variablelist>
        <varlistentry>
          <term>^ (beginning of line)</term>

          <listitem>
            <para>Frequently required for rules to work correctly.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term>$ (end of line)</term>

          <listitem>
            <para>Frequently required for rules to work correctly. For
            example:</para>

            <screen>\.c$ ## matches only file names with the extension, <filename>c</filename>.
\.c  ## matches any extension beginning with <filename>c</filename>, like <filename>cpp</filename> and <filename>com</filename>.</screen>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term>\ (escape)</term>

          <listitem>
            <para>Forces special characters to match normal characters. For
            example, to match a folder name, precede the folder backslash
            delimiter with a backslash (<code>\\</code>). To match the dot in a
            file name, specify a backslash followed by a dot
            (<code>\.</code>).</para>
          </listitem>
        </varlistentry>
      </variablelist>

      <para>No special characters or wildcards are used to match file names. To
      match all filenames of a certain type, simply omit the filename.</para>

      <para>Rules are case-insensitive. For example, <code>f: \.bat$</code>
      matches <filename>winmerge.bat</filename> and
      <filename>compare.BAT</filename>.</para>

      <example>
        <title>File filter rule examples</title>

        <para>Some simple file filter rules:</para>

        <screen>f: \.cpp$ ## Match <filename>*.cpp</filename> files
f: \.h$ ## Match <filename>*.h</filename> files
f: ^My ## Match <filename>My*.*</filename> files
f: Dlg\. ## Match <filename>*Dlg.*</filename> files
d: \\test$ ## Match <filename>test</filename> folders
d: ^\\Build$ ## Match <filename>Build</filename> folders
d: Temp$ ## Match <filename>*Temp</filename> folders (for example, <filename>FirstTemp</filename>)
d: Src ## Match <filename>*Src*</filename> folders</screen>

        <para>Some rules with more complex regular expressions:</para>

        <screen format="linespecific">f: ^\.#.*$ ## <filename>.#filename.version</filename> files
f: Dlg\.c(pp)?$ ## <filename>*Dlg.c</filename> and <filename>*Dlg.cpp</filename> files
f: ^I.*\.h$ ## <filename>I*.h</filename> files
f: Srv[1-9]\.def$ ## <filename>*Srv1.def</filename> to <filename>*Srv9.def</filename> files
f: ^[h,k,m] ## <filename>h*.*</filename>, <filename>k*.*</filename>, and <filename>m*.*</filename> files</screen>
      </example>
    </section>
  </section>

  <section id="Filters_LineFilter">
    <title>Using line filters<indexterm>
        <primary>filters</primary>

        <secondary>line</secondary>
      </indexterm><indexterm>
        <primary>filters</primary>

        <secondary>in file comparisons</secondary>
      </indexterm></title>

    <para>In a file comparison, you can use line filters to ignore single lines.
    For example, you might use line filters to ignore comments or certain type
    of generated code, like version control system timestamps. Each line filter
    is a rule, and you can apply any number of line filters to a file
    comparison.</para>

    <para>To learn how to add, edit, and manage filters, see <xref
    linkend="Filters_dlg" />.</para>

    <section id="Filters_LineFilterApply">
      <title>Applying line filters</title>

      <para>You can apply line filters using any of these methods:</para>

      <itemizedlist>
        <listitem>
          <para>When you launch a file compare from the Select Files or Folders
          dialog</para>

          <orderedlist>
            <listitem>
              <para>After choosing the <guilabel>Left</guilabel> and
              <guilabel>Right</guilabel> files, click
              <guibutton>Select</guibutton> next to the
              <guilabel>Filter</guilabel> field.</para>
            </listitem>

            <listitem>
              <para>In the Filters dialog, use the Linefilters tab to enable the
              line filters you want to use (if any), or to see what line filters
              are currently enabled.</para>

              <note>
                <para>The <guilabel>Filter</guilabel> field does not indicate
                what line filters are enabled.</para>
              </note>
            </listitem>

            <listitem>
              <para>Proceed with the file compare operation. The enabled line
              filters are applied when you start the operation.</para>
            </listitem>
          </orderedlist>
        </listitem>

        <listitem>
          <para>After you have already launched a file compare operation (for
          example, to apply different filters or disabling filtering)</para>

          <orderedlist>
            <listitem>
              <para>Click <menuchoice>
                  <guimenu>Tools</guimenu>

                  <guimenuitem>Filters</guimenuitem>
                </menuchoice>.</para>
            </listitem>

            <listitem>
              <para>Open the Filefilters tab.</para>
            </listitem>

            <listitem>
              <para>Check the individual line filters you want to apply, and
              uncheck filters that you don't want to apply.</para>

              <para>You can also add, edit, and remove filters from the list by
              using the <guibutton>New</guibutton>, <guibutton>Edit</guibutton>,
              and <guibutton>Remove</guibutton> buttons.</para>
            </listitem>

            <listitem>
              <para>To turn on line filtering, check the <guilabel>Enable Line
              Filters</guilabel>. To turn line filtering off, uncheck the
              option.</para>
            </listitem>

            <listitem>
              <para>Click <guibutton>OK</guibutton> to dismiss the File Filters
              dialog.</para>
            </listitem>

            <listitem>
              <para>Click <keycap>F5</keycap> to apply your changes and refresh
              the File Compare window.</para>
            </listitem>
          </orderedlist>
        </listitem>
      </itemizedlist>
    </section>

    <section id="Filters_LineFilterSyntax">
      <title>Line filter syntax<indexterm>
          <primary>rules</primary>

          <secondary>line filter</secondary>
        </indexterm><indexterm>
          <primary>filters</primary>

          <secondary>line</secondary>
        </indexterm><indexterm>
          <primary>regular expressions</primary>

          <secondary>in line filters</secondary>
        </indexterm></title>

      <para>A line filter is a rule that is evaluated against each single-line
      difference in your compared files, if line filter rules are enabled. When
      a rule matches a single-line difference, the difference is ignored.</para>

      <para>Ignored differences are marked in the File Compare window with the
      <guilabel>Ignored Difference</guilabel> color (as defined in the Colors
      page of WinMerge Options). This enables you to distinguish ignored
      differences from other types. However, you cannot select or merge ignored
      difference.</para>

      <para>Line filter matching can be described in terms of two ideas:</para>

      <itemizedlist>
        <listitem>
          <para>When a rule matches any part of the line, the entire difference
          is ignored. Therefore, you cannot filter just part of a line. For
          example, suppose two files have the following single-line
          difference:</para>

          <formalpara>
            <title>File1:</title>

            <para><screen># Jean Sibelius</screen></para>
          </formalpara>

          <formalpara>
            <title>File2:</title>

            <para><screen># Janne Sibelius</screen></para>
          </formalpara>

          <para>With no filtering, the line is detected as a difference. But if
          we apply a line filter rule with the expression, <code>^#</code>, the
          lines are reported as identical, because the expression specifies only
          the first character, which matches in both files.</para>
        </listitem>

        <listitem>
          <para>A rule is applied to a multi-line difference only if all the
          lines match. For example, consider this two-line difference:</para>

          <formalpara>
            <title>File1:</title>

            <para><screen># Jean Sibelius
# Pekka Himanen</screen></para>
          </formalpara>

          <formalpara>
            <title>File2:</title>

            <para><screen># Janne Sibelius
Pekka Himanen</screen></para>
          </formalpara>

          <para>The same <code>^#</code> rule matches the first line, but not
          the second line. Therefore, the difference is not ignored.</para>
        </listitem>
      </itemizedlist>

      <tip>
        <para>It's usually good practice to use the beginning of line (
        <code>^</code> ) and end of line ( <code>$</code> ) markers to
        control your patterns precisely, because the rule is applied if any part
        of a line matches the expression.</para>
      </tip>

      <example>
        <title>Sample line filters</title>

        <screen format="linespecific">^MYTAG$</screen>

        <para>Filters lines that exactly match <literal>MYTAG</literal></para>

        <screen format="linespecific">^::</screen>

        <para>Filters lines beginning with <literal>::</literal></para>

        <screen format="linespecific">^/\*.*\*/$</screen>

        <para>Filters lines beginning with
        <literal><constant>/*</constant></literal> and ending with
        <literal>*/</literal></para>

        <screen format="linespecific">^[1-5]00</screen>

        <para>Filters lines beginning with numbers 100, 200, 300, 400, and
        500</para>
      </example>

      <example>
        <title>Line filter rule matching CVS Id lines</title>

        <para>CVS Id lines look like this:</para>

        <screen>// $Id: Filters.xml 7591 2013-01-20 15:47:42Z christianlist $</screen>

        <para>... and can be filtered with this rule:</para>

        <screen>^// \WId: .*\$</screen>
      </example>

      <example>
        <title>Filter line number comments in po files</title>

        <para>po line number comments look like this:</para>

        <screen>#: src/filename.c:766</screen>

        <para>... and can be filtered with this rule:</para>

        <screen>^#</screen>
      </example>
    </section>
  </section>

  <section id="Filters_dlg">
    <title>Using the Filters dialog<indexterm>
        <primary>Filters dialog</primary>
      </indexterm><indexterm>
        <primary>filters</primary>

        <secondary>managing and enabling</secondary>
      </indexterm></title>

    <para>This section describes the Filters dialog, which provides functions to
    create and manage file filters and line filters.</para>

    <para>To open the Filters dialog, use either of these methods:</para>

    <itemizedlist>
      <listitem>
        <para>In the Select Files or Folders dialog, click
        <guibutton>Select</guibutton> to the right of the
        <guilabel>Filter</guilabel> field. You use this method when you want to
        apply a file filter to a folder compare operation.</para>
      </listitem>

      <listitem>
        <para>Click <menuchoice>
            <guimenu>Tools</guimenu>

            <guimenuitem>Filters</guimenuitem>
          </menuchoice>. This method can be used at any time except when the
        Select Files or Folders dialog is open.</para>
      </listitem>
    </itemizedlist>

    <para>The Filters dialog has a tab for each type of WinMerge filter:</para>

    <variablelist>
      <varlistentry>
        <term>Filefilters</term>

        <listitem>
          <para>Choose this tab to work with file filters for folder compare
          operations.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>Linefilters</term>

        <listitem>
          <para>Choose this tab to work with line filters for file compare
          operations.</para>
        </listitem>
      </varlistentry>
    </variablelist>

    <section id="Filters_FileFiltersTab">
      <title>Using the Filefilters tab<indexterm>
          <primary>file filters</primary>

          <secondary>enabling</secondary>
        </indexterm></title>

      <para>The main part of this tab is a list of file filters that are
      available for folder compare operations. The list includes shared,
      private, and installed file filters that WinMerge knows about, as
      described in <xref linkend="Filters_FileFilterLoc" />.</para>

      <section id="Filters_FileFilterEnabling">
        <title>Enabling and disabling file filters</title>

        <para>You must enable a file filter to make it available in a folder
        comparison operation, or to disable a current filter to stop it from
        being used:</para>

        <orderedlist>
          <listitem>
            <para>Open the Filters dialog, if it is not already open.</para>
          </listitem>

          <listitem>
            <para>Select a file filter or
            <guimenuitem>&lt;None&gt;</guimenuitem> from the list.</para>
          </listitem>

          <listitem>
            <para>Click <guibutton>OK</guibutton> to dismiss the Filters
            dialog.</para>
          </listitem>
        </orderedlist>

        <para>There are several ways to apply file filters after enabling them.
        For details, see <xref linkend="Filters_FileFilterApply" />.</para>
      </section>

      <section id="Filters_FileFilterCfg">
        <title>Configuring file filters</title>

        <para>Use these buttons to manage your <guilabel>Filefilters</guilabel>
        list and create new file filters:</para>

        <variablelist>
          <varlistentry>
            <term>Test</term>

            <listitem>
              <para>Select a file filter in the list and click
              <guibutton>Test</guibutton> to quickly see how the filter works.
              See <xref linkend="Filters_TestingDlg" /> for details.</para>
            </listitem>
          </varlistentry>

          <varlistentry>
            <term>Install</term>

            <listitem>
              <para>Enables you to locate a file filter and adds it to the
              Filters list. File filters that are not in either the shared or
              default private folder are not detected unless you install
              them.</para>
            </listitem>
          </varlistentry>

          <varlistentry>
            <term>New</term>

            <listitem>
              <para>Creates a new copy of a file template in either the shared
              or private filter folders, and opens it in your default editor.
              Edit the template and add your rules, as described in <xref
              linkend="Filters_CreatingFile" />.</para>
            </listitem>
          </varlistentry>

          <varlistentry>
            <term>Edit</term>

            <listitem>
              <para>Select a file filter in the list and click
              <guibutton>Edit</guibutton> to open the file in your default
              editor.</para>
            </listitem>
          </varlistentry>

          <varlistentry>
            <term>Delete</term>

            <listitem>
              <para>Select a file filter in the list and click
              <guibutton>Delete</guibutton> to delete the file and remove it
              from the list. Yes, the file is really deleted!</para>
            </listitem>
          </varlistentry>
        </variablelist>

        <para>Your changes are saved when you click <guibutton>OK</guibutton> to
        dismiss the Filters dialog. Line filters are stored in the Windows
        registry.</para>
      </section>

      <section id="Filters_CreatingFile">
        <title>Creating a file filter</title>

        <para>If the file filters that are installed with WinMerge do not
        provide the filtering you need, you can create your own:</para>

        <orderedlist>
          <listitem>
            <para>Click <menuchoice>
                <guimenu>Tools</guimenu>

                <guimenuitem>Filters</guimenuitem>
              </menuchoice>. Or, from the Select Files or Folders dialog, click
            <guibutton>Select</guibutton> to the right of the
            <guilabel>Filter</guilabel> field.</para>
          </listitem>

          <listitem id="Filters_New_step">
            <para>In the Filters dialog Filefilters tab, click
            <guibutton>New</guibutton>.</para>
          </listitem>

          <listitem>
            <para>In the Shared or Private Filter dialog, choose
            <guilabel>Shared Filter</guilabel> or <guilabel>Private
            Filter</guilabel> (see <xref linkend="Filters_FileFilterLoc" /> for
            their uses) and click <keycap>OK</keycap>.</para>

            <para>The Select filename for new filter dialog opens in the shared
            or private files folder on your system (if the private folder does
            not exist, WinMerge creates it).</para>
          </listitem>

          <listitem>
            <para>In the Select filename for new filter dialog, enter a new file
            name and click <guibutton>Save</guibutton>.</para>

            <note>
              <para>Don't choose an existing file name: to edit an existing
              file, go back to Step <xref linkend="Filters_New_step" /> and
              click Edit instead of New.</para>
            </note>

            <para>WinMerge initializes the new file with the contents of the
            <filename>FileFilter.tmpl</filename> tempate, and opens it in your
            default text editor.</para>
          </listitem>

          <listitem>
            <para>Follow the template instructions to edit the template,
            updating the placeholder name and description and adding filter
            rules as described in <xref linkend="Filters_FileFilterSyntax" />.
            Save the file in your text editor.</para>

            <tip>
              <para>If you want to quickly test a rule that you are defining,
              try clicking Test in the Filters dialog. See <xref
              linkend="Filters_TestingDlg" /> for details.</para>
            </tip>
          </listitem>

          <listitem>
            <para>If you created your file filter in one of the standard
            <filename>Filters</filename> folders, and the Filters dialog does
            not list your new file filter, try clicking
            <guibutton>OK</guibutton> to close it, then click <menuchoice>
                <guimenu>Tools</guimenu>

                <guimenuitem>Filters</guimenuitem>
              </menuchoice> again to reopen it. The
            <guilabel>Filefilters</guilabel> list should now include the new
            file filter.</para>

            <para>If you saved the file in an alternate location on your file
            system), WinMerge cannot detect it unless you install it. To make a
            file filter detectable anywhere on your system:</para>

            <orderedlist numeration="loweralpha">
              <listitem>
                <para>Click <guibutton>Install</guibutton> in the Filters
                dialog.</para>
              </listitem>

              <listitem>
                <para>In the Locate filter file to install dialog, navigate to
                the <filename>flt</filename> file on your system, and click
                <guibutton>Open</guibutton>. The Filefilters list should now
                include the installed file filter.</para>
              </listitem>
            </orderedlist>
          </listitem>
        </orderedlist>
      </section>

      <section id="Filters_TestingDlg">
        <title>Testing file filter rules<indexterm>
            <primary>file filters</primary>

            <secondary>testing</secondary>
          </indexterm><indexterm>
            <primary>testing file filters</primary>
          </indexterm></title>

        <para>Use the Test Filter dialog to quickly test a file filter against
        sample data, to help you develop new rules or to understand how existing
        rules work. It can be easier than running a full compare
        operation.</para>

        <para>Starting from the Filters dialog:</para>

        <orderedlist>
          <listitem>
            <para>In the Filefilters tab, choose the file filter you want to
            test.</para>
          </listitem>

          <listitem>
            <para>If you want to see the rules you will be testing,click
            <guibutton>Edit</guibutton> now to open the file so that you can
            view it during the next steps.</para>
          </listitem>

          <listitem>
            <para>Click <guibutton>Test</guibutton>.</para>
          </listitem>

          <listitem>
            <para>In the Test Filter dialog, choose the type of rule to
            test:</para>

            <itemizedlist>
              <listitem>
                <para>To test an <guilabel>f:</guilabel> file rule in your file
                filter, uncheck the <guilabel>Folder Name</guilabel>
                option.</para>
              </listitem>

              <listitem>
                <para>To test a <guilabel>d:</guilabel> folder rule, check the
                <guilabel>Folder Name</guilabel> option.</para>
              </listitem>
            </itemizedlist>
          </listitem>

          <listitem>
            <para>Enter the text to test.</para>

            <para>The text should be appropriate for the type of rule you are
            testing. For example, if you have checked the <guilabel>Folder
            Name</guilabel> option, you probably want to enter a folder name,
            such as \temp.</para>

            <para>The <guilabel>Result</guilabel> box displays your entry,
            followed by its status: either
            <computeroutput>passed</computeroutput> or
            <computeroutput>failed</computeroutput>.</para>
          </listitem>
        </orderedlist>
      </section>
    </section>

    <section id="Filters_LineFiltersTab">
      <title>Using the Linefilters tab<indexterm>
          <primary>line filters</primary>

          <secondary>enabling</secondary>
        </indexterm></title>

      <para>Use this tab to configure and enable line filters for file compare
      operations. The tab features a list of rules. Each rule contains a single
      regular expression. You can apply any combination of rules from the list
      to a file comparison.</para>

      <section id="Filters_LineFilterCfg">
        <title>Configuring line filters</title>

        <para>Below the <guilabel>Regular Expressions</guilabel> list is an edit
        box and buttons that you can use to maintain the list at any time by
        adding, editing, and removing rules.</para>

        <para>To add a new rule:</para>

        <orderedlist>
          <listitem>
            <para>Click <guibutton>New</guibutton>. Your edit cursor is
            automatically enabled in the edit box.</para>
          </listitem>

          <listitem>
            <para>Enter an expression in the edit box below the
            <guilabel>Regular Expressions</guilabel> list.</para>
          </listitem>

          <listitem>
            <para>Click <guibutton>Save</guibutton> to load the expression in a
            new line in the list.</para>
          </listitem>
        </orderedlist>

        <para>To edit an existing rule:</para>

        <orderedlist>
          <listitem>
            <para>Select the line and click <guibutton>Edit</guibutton>.</para>
          </listitem>

          <listitem>
            <para>Edit the expression in the edit box.</para>
          </listitem>

          <listitem>
            <para>Click <guibutton>Save</guibutton><guibutton> </guibutton>when
            you're done.</para>
          </listitem>
        </orderedlist>

        <para>To delete an existing rule, select (check) the rule and click
        <guibutton>Remove</guibutton>.</para>
      </section>

      <section id="Filters_LineFilterEnabling">
        <title>Enabling and disabling line filters<indexterm>
            <primary>line filters</primary>

            <secondary>list of available</secondary>
          </indexterm></title>

        <orderedlist>
          <listitem>
            <para>In the <guilabel>Regular Expressions</guilabel> list, check
            just the filters that you want to apply, and uncheck any filters you
            do not want to apply.</para>
          </listitem>

          <listitem>
            <para>Check or uncheck the <guilabel>Enable Line Filters</guilabel>
            option. If you turn filtering on, all the rules that are currently
            checked in the <guilabel>Regular Expression</guilabel> list are
            used. If filtering is off, no rules are used even if they are
            checked.</para>
          </listitem>

          <listitem>
            <para>Click <guibutton>OK</guibutton> to dismiss the Filters dialog
            and save your settings.</para>
          </listitem>
        </orderedlist>

        <para>There are several ways to apply file filters after enabling them.
        For details, see <xref linkend="Filters_LineFilterApply" />.</para>
      </section>
    </section>
  </section>

  <section id="AboutFilters_regexp">
    <title>Getting help with regular expressions<indexterm>
        <primary>regular expressions</primary>

        <secondary>getting help</secondary>
      </indexterm></title>

    <para>Regular expressions can be very complex. Fortunately, most file
    filters in WinMerge involve simple extension expressions, as shown in the
    examples in this topic. The filter files installed with WinMerge include
    many other useful examples.</para>

    <para>Finally, there are lots of resources on the Web for help with regexps,
    including these sites:</para>

    <variablelist>
      <varlistentry>
        <term>Good site devoted to regexps:</term>

        <listitem>
          <simpara><ulink
          url="https://www.regular-expressions.info/">http://www.regular-expressions.info/</ulink></simpara>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>Tutorial:</term>

        <listitem>
          <simpara><ulink
          url="http://www.zvon.org/comp/r/tut-Regexp.html">http://www.zvon.org/comp/r/tut-Regexp.html</ulink></simpara>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>PDF quick reference:</term>

        <listitem>
          <simpara><ulink
          url="https://github.com/GordonMcKinney/gist-assets/raw/master/regex.pdf">
          https://github.com/GordonMcKinney/gist-assets/raw/master/regex.pdf</ulink></simpara>
        </listitem>
      </varlistentry>
    </variablelist>
  </section>
</article>
