<?xml version="1.0" encoding="UTF-8"?>
<article id="Intro_diffs">
  <title>Overview of file comparing and merging</title>

  <para>This topic describes how WinMerge detects and displays differences
  within text files, and demonstrates simple file comparing and merging
  operations. See <xref linkend="Intro_diffs" /> for related information about
  hex files. </para>

  <section id="Intro_diffs_comparing">
    <title>Comparing files<indexterm>
        <primary>comparing files</primary>

        <secondary>overview</secondary>
      </indexterm></title>

    <para>We usually compare two files that are related in some way, such as two
    versions that were edited at different times, or by different people. If you
    examine two such files you can usually see some similar areas, and also
    identify several types of differences: different characters and words,
    different lines, even entire blocks of text that are different. But trying
    to understanding all the differences between two files by scanning them in
    your favorite editor can be tedious and error-prone. Specialized
    difference/merging tools like WinMerge are designed make this work more
    systematic and efficient.</para>

    <para>A simple difference utility that most people have used is a spell
    checker: it systematically steps you through a document, highlights words
    that are different from those in its dictionary, and helps you resolve each
    spelling problem. However, looking only at characters and words is not an
    effective way to understand differences between multiple files. For this
    reason, many difference utilities use lines as the basic unit of comparison
    instead.</para>

    <para>WinMerge also uses lines as its basic unit of difference. Words and
    characters are not treated individually in comparing and merging operations.
    To illustrate, consider two files that are identical except for one line
    that is different. If the two versions of the line have four words that are
    different and one version has an extra space, then we say that the file has
    one difference, not five.</para>

    <para>If it's quicker to compare lines than words, sometimes it's also
    useful to treat an entire block of lines as a single difference, instead of
    comparing one line at a time. As we will see later, detecting multiple-line
    differences makes merging more efficient too.</para>

    <section>
      <title>Simple compare operation</title>

      <para>This section offers a simple example that demonstrates how to
      compare line differences between two files in WinMerge:</para>

      <orderedlist>
        <listitem>
          <para>Using a text editor, create two files with the names and
          contents shown here, being careful to preserve the words and line
          breaks exactly:</para>

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

            <para><screen>It's slow comparing words 
and characters. Instead,  
WinMerge compares lines.
Believe it or else.</screen></para>
          </formalpara>

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

            <para><screen>It's slow comparing words.
WinMerge compares lines.
Believe it or not.</screen></para>
          </formalpara>
        </listitem>

        <listitem>
          <para>Start WinMerge. For example, double-click the <inlinemediaobject>
              <imageobject>
                <imagedata contentwidth="32" fileref="screenshots/wm_icon.png" />
              </imageobject>

              <textobject>
                <phrase>WinMerge desktop shortcut</phrase>
              </textobject>
            </inlinemediaobject> WinMerge desktop shortcut.</para>
        </listitem>

        <listitem>
          <para>In the Select Files and Folders dialog, specify
          <filename>File1</filename> as the <guilabel>1st</guilabel> file and
          <filename>File2</filename> as the <guilabel>2nd</guilabel> file,
          then click <guibutton>Compare</guibutton>. The File Compare window displays
          the two files in the left and right File pane, like this:</para>

          <mediaobject>
            <imageobject>
              <imagedata contentwidth="600"
                         fileref="screenshots/missing_lines.png" />
            </imageobject>

            <textobject>
              <phrase>Compare Files screen shot</phrase>
            </textobject>
          </mediaobject>

          <para>The elements are described in more detail in <xref
          linkend="Compare_files" />. Here are some features you should notice
          in this example:</para>

          <variablelist>
            <varlistentry>
              <term>Number of differences</term>

              <listitem>
                <para>The message in the status bar at the bottom of the
                WinMerge window tells you that two differences were
                detected.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term>Difference colors</term>

              <listitem>
                <para>Difference blocks are marked with the difference
                background color (gold, by default).</para>

                <para>Line differences can be enabled to mark changed text
                within differences blocks, using the word background color
                (light yellow, by default).</para>

                <para>Identical lines are unmarked: they have white backgrounds,
                like the third line in the example.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term>Blank lines</term>

              <listitem>
                <para>Notice that in the left comparison pane, the second line
                has text: the other pane has a blank gray line in the same
                location. This blank line does not exist in the
                <filename>File2</filename> source file, so what is it doing in
                WinMerge?</para>

                <para>WinMerge inserts one or more gray blank lines in one
                version of a difference when the other version has more lines.
                These empty gray lines do not represent blank lines in the
                source file; they are only placeholders in the display. The
                purpose of placeholder lines is to keep the left and right
                versions of differences vertically aligned. Thus in our example,
                the text, <computeroutput>WinMerge compares
                lines</computeroutput>, appears side by side in the Comparison
                window, even though they are on different lines in the source
                files. This makes it easier to compare differences in WinMerge
                than in a conventional editor.</para>

                <tip>
                  <para>One consequence of the blank lines is that both panes in
                  the File Compare window always display the same total number
                  of lines, even if their source files do not.</para>
                </tip>
              </listitem>
            </varlistentry>
          </variablelist>

          <para>Now that you understand how WinMerge detects and displays
          differences, you can use the comparing functions effectively, as shown
          in the next steps.</para>
        </listitem>

        <listitem>
          <para>Click <inlinemediaobject>
              <imageobject>
                <imagedata contentdepth="15"
                           fileref="screenshots/currentdiff_btn.png" />
              </imageobject>

              <textobject>
                <phrase>Current Difference button</phrase>
              </textobject>
            </inlinemediaobject> <guibutton>Current Difference</guibutton> in
          the toolbar (or press <keycombo>
              <keycap>Alt</keycap>

              <keycap>Enter</keycap>
            </keycombo>). If this button is not enabled (for example, if your
          cursor is in a different line), click <inlinemediaobject>
              <imageobject>
                <imagedata contentdepth="15"
                           fileref="screenshots/firstdiff_btn.png" />
              </imageobject>

              <textobject>
                <phrase>First Difference button</phrase>
              </textobject>
            </inlinemediaobject> First Difference (or press <keycombo>
              <keycap>Alt</keycap>

              <keycap>Home</keycap>
            </keycombo>) instead.</para>

          <para>When you select a difference, the two versions are loaded in the
          Diff pane. The Diff pane confirms which lines are included in a
          difference, and lets you examine them in isolation from the rest of
          the file. In our example, Difference 1 clearly has two lines.</para>

          <mediaobject>
            <imageobject>
              <imagedata contentwidth="588"
                         fileref="screenshots/filecomp_diffpane1.png" />
            </imageobject>

            <textobject>
              <phrase>Compare Files Diff Pane</phrase>
            </textobject>
          </mediaobject>
        </listitem>

        <listitem>
          <para>Click <inlinemediaobject>
              <imageobject>
                <imagedata contentdepth="15"
                           fileref="screenshots/nextdiff_btn.png" />
              </imageobject>

              <textobject>
                <phrase>Current Difference button</phrase>
              </textobject>
            </inlinemediaobject> <guibutton>Next Difference</guibutton> in the
          toolbar (or click <keycombo>
              <keycap>Alt</keycap>

              <keycap>Enter</keycap>
            </keycombo>). This jumps over the identical line (which is not a
          difference) and selects the last line.</para>

          <para>You have reached the end of the file and had a chance to examine
          every difference. This was a trivial example — there were only two
          differences — and there are other ways to compare differences in
          WinMerge. But it demonstrates the efficiency of using the WinMerge
          navigation controls.</para>
        </listitem>
      </orderedlist>
    </section>
  </section>

  <section id="Intro_diffs_merging">
    <title>Merging files<indexterm>
        <primary>merging differences</primary>

        <secondary>overview and example</secondary>
      </indexterm></title>

    <para>The purpose of merging is to combine changes from two files into one
    file. Merging extends the concepts and functions used in comparing
    operation: please read the preceding section before beginning this section.
    In addition to detecting differences between two file versions, we resolve
    the differences and save the result in a single
    <glossterm>target</glossterm> version.</para>

    <para>Merging files makes concurrent development possible, and it is a
    common task in team environments. For example, suppose you and another
    person want to add code to the same program file at the same time. You both
    begin with an identical copy of the file, but during development you create
    separate versions that are not identical. At some point, the two versions
    must be merged into one version that preserves the changes from each
    contributor.</para>

    <para>Merging can be prompted (or even initiated) by version control systems
    like Subversion and Git. For example, your version control system
    might prevent you from submitting changes to its repository because of merge
    conflicts. A conflict can occur if someone else checked in a different
    version of the same file while you were working on your version, and the
    version control system was not able to automatically merge the differences.
    When that happens, you might need to merge the conflicting versions before
    trying again to contribute your version. Many systems have integrated
    difference and merge tools, but you might prefer to use WinMerge
    instead.</para>

    <para>Just as with comparing, you use WinMerge's toolbar controls (or
    keyboard shortcuts) to systematically step through the differences. Resolve
    each difference by copying either its left or right
    <glossterm>candidate</glossterm> to the other side. When you have resolved
    all the differences, WinMerge lets you know that all differences are
    resolved (the versions are identical), and you are done merging.</para>

    <section>
      <title>Simple merge operation</title>

      <para>This short exercise demonstrates how to use the controls in the File
      Compare window in a systematic way to merge the simple files shown
      earlier:</para>

      <orderedlist>
        <listitem>
          <para>Click <inlinemediaobject>
              <imageobject>
                <imagedata contentdepth="15"
                           fileref="screenshots/currentdiff_btn.png" />
              </imageobject>

              <textobject>
                <phrase>Current Difference button</phrase>
              </textobject>
            </inlinemediaobject> <guibutton>Current Difference</guibutton> in
          the toolbar to select the first difference. If this button is not
          enabled, click <inlinemediaobject>
              <imageobject>
                <imagedata contentdepth="15"
                           fileref="screenshots/firstdiff_btn.png" />
              </imageobject>

              <textobject>
                <phrase>First Difference button</phrase>
              </textobject>
            </inlinemediaobject> <guibutton>First Difference</guibutton>
          instead.</para>
        </listitem>

        <listitem>
          <para>Click <inlinemediaobject>
              <imageobject>
                <imagedata contentwidth="17"
                           fileref="screenshots/copyr_button.png" />
              </imageobject>

              <textobject>
                <phrase>Copy Right button</phrase>
              </textobject>
            </inlinemediaobject> <guibutton>Copy Right</guibutton> to merge
          difference 1 from <filename>File1</filename> to
          <filename>File2</filename>. In <filename>File</filename>2, notice that
          the single difference line is replaced by the two lines from
          <filename>File1</filename>, and the gray blank line is now
          gone.</para>
        </listitem>

        <listitem>
          <para>Click <inlinemediaobject>
              <imageobject>
                <imagedata contentdepth="15"
                           fileref="screenshots/nextdiff_btn.png" />
              </imageobject>

              <textobject>
                <phrase>Next Difference button</phrase>
              </textobject>
            </inlinemediaobject> <guibutton>Next Difference</guibutton> to
          select Difference 2. This is easier than finding and selecting the
          difference yourself. It's especially useful if you want to step
          through all differences without accidentally missing any.</para>
        </listitem>

        <listitem>
          <para>Click <inlinemediaobject>
              <imageobject>
                <imagedata contentwidth="17"
                           fileref="screenshots/copyl_button.png" />
              </imageobject>

              <textobject>
                <phrase>Copy Left button</phrase>
              </textobject>
            </inlinemediaobject> <guibutton>Copy Left</guibutton> to merge
          Difference 2 from <filename>File2</filename> to
          <filename>File1</filename>.</para>

          <para>The message that the files are identical tells you that the
          merge is complete:</para>

          <mediaobject>
            <imageobject>
              <imagedata contentwidth="600"
                         fileref="screenshots/filemerged1.png" format="PNG" />
            </imageobject>
          </mediaobject>
        </listitem>

        <listitem>
          <para>Click <guibutton>OK</guibutton> to dismiss the message. The
          status Difference message changes from <computeroutput>Difference 1 of
          1</computeroutput> to
          <computeroutput>identical</computeroutput>.</para>
        </listitem>

        <listitem>
          <para>Press <keycombo>
              <keycap>Ctrl</keycap>

              <keycap>S</keycap>
            </keycombo> to save your changes.</para>
        </listitem>
      </orderedlist>

      <para>While very simple, this example demonstrates a basic methodology
      that you can use to step through a comparison of any length, merging each
      difference one by one until you have the result that you want.</para>
    </section>

    <section>
      <title>Choosing a merge result file <indexterm>
          <primary>merging differences</primary>

          <secondary>result file</secondary>
        </indexterm><indexterm>
          <primary>result file, in merge</primary>
        </indexterm></title>

      <para>You control where your merge result is preserved. The WinMerge File
      Compare window does not have a separate result pane, as some merge tools
      do. So the simplest strategy is to save your changes to one or both source
      files. Press <keycombo>
          <keycap>Ctrl</keycap>

          <keycap>S</keycap>
        </keycombo> at any time to save the current changes to both files;
      alternatively, click <menuchoice>
          <guimenu>File</guimenu>

          <guimenuitem>Save Left</guimenuitem>
        </menuchoice> or <menuchoice>
          <guimenu>File</guimenu>

          <guimenuitem>Save Right</guimenuitem>
        </menuchoice> to save only one file.</para>

      <para>To write to a third file instead of either source file, use
      <menuchoice>
          <guimenu>File</guimenu>

          <guimenuitem>Save As</guimenuitem>
        </menuchoice>. For example, your target file might be the difference or
      conflict file generated by a version control system.</para>

      <para>Similarly, in the WinMerge command line, you can leave both source
      versions unchanged by using the optional <option>outputfile</option>
      argument, as described in <xref linkend="Command_line" />.</para>
    </section>
  </section>
</article>