advanced: diff

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+---
+layout: page
+author: Alessandro Luini
+category-page: advanced
+category-title: Advanced commands
+tags: difference lines diff file separating
+title: diff
+---
+
+
+
+
+
+<p> diff analyzes two files and prints the lines that are different.
+   Essentially, it outputs a set of instructions for how to change one file to
+   make it identical to the second file.</p>
+
+
+
+
+
+
+
+   <h3>How to use</h3>
+
+     <p> To activate the diff command, we must take as parameters two or more
+       files that we want to compare and it will give us the output of
+        different lines. <br>
+        For example let's say we have two files, file1.txt and file2.txt.<br>
+        <br> If <b>file1.txt</b> contains the following four lines of text: </p>
+
+<ol><code><li>I need to buy apples.</li>
+<li>I need to run around the park.</li>
+<li>I need to wash the dog.</li>
+<li>I need to get the car detailed.</li></code></ol>
+
+<p> ...and <b>file2.txt</b> contains these four lines: </p>
+
+<ol><code><li> I need to buy apples.</li>
+<li>I need to do the laundry.</li>
+<li>I need to wash the dog.</li>
+<li>I need to get the dog detailed.</li></ol></code>
+
+<p>...then we can use diff to automatically display for us which lines differ
+   between the two files with this command:</p>
+
+   <pre>diff file1.txt file2.txt</pre>
+
+   <p> ...and the output will be:</p>
+
+   <pre> 2,4c2,4 <br>
+< I need to run the laundry.<br>
+< I need to wash the dog.<br>
+< I need to get the car detailed.<br>
+---<br>
+> I need to do the laundry.<br>
+> I need to wash the car.<br>
+> I need to get the dog detailed.</pre>
+
+<p> In our output above, "2,4c2,4" means: "Lines 2 through 4 in the first
+  file need to be changed to match lines 2 through 4 in the second file.</p>
+
+
+
+
+
+
+
+   <h3>Flags</h3>
+   <ul>
+     <li><h4> -c:</h4> <br>To view differences in context mode, use the -c option.
+        For instance, let's say <b>file1.txt</b> and <b>file2.txt</b> contain
+        the following:<br><br>
+
+<table>
+<tr>
+      <th> File1.txt </th> <th>File2.txt</th></tr>
+      <tr><td> apples </td> <td>apples</td></tr>
+      <tr><td>oranges</td> <td>kiwis</td></tr>
+      <tr><td>kiwis</td>   <td>carrots</td></tr>
+      <tr><td>carrots</td>  <td>grapefruits</td></tr></table>
+
+
+
+
+
+
+
+
+
+       <pre> diff -c file1.txt file2.txt </pre>
+
+       Our output will be like the following:
+  <pre>     *** file1.txt   2014-08-21 17:58:29.764656635 -0400<br>
+--- file2.txt   2014-08-21 17:58:50.768989841 -0400<br>
+***************<br>
+*** 1,4 ****<br>
+  apples<br>
+- oranges<br>
+  kiwis<br>
+  carrots<br>
+--- 1,4 ----<br>
+  apples<br>
+  kiwis<br>
+  carrots<br>
++ grapefruits< </pre>
+
+       The first two lines of this output show us information about our "from"
+       file (file 1) and our "to" file (file 2). It lists the file name,
+       modification date, and modification time of each of our files, one per
+       line. The "from" file is indicated by "***", and the "to" file is
+       indicated by "---"..<br>
+     <br> The line "***************" is just a separator.
+     <br><br> The next line has three asterisks ("***") followed by a line
+     range from the first file (in this case lines 1 through 4, separated by
+     a comma). Then four asterisks ("****").<br>
+   <br> Then it shows us the contents of those lines. If the line is unchanged,
+   it's prefixed by two spaces. If the line is changed, however, it's prefixed
+   by an indicative character and a space. The character meanings are as
+   follows:<br><br>
+
+
+
+
+
+<table> <tr>
+  <th>Character</th>
+  <th>Meaning</th></tr>
+  <tr> <td> <b>!</b></td>
+    <td>Indicates that this line is part of a group of one or more lines that
+      needs to change. There is a corresponding group of lines prefixed with
+      "!" in the other file's context as well.</td></tr>
+      <tr><td><b>+</b></td>
+        <td>Indicates a line in the second file that needs to be added to the
+          first file.</td></tr>
+          <tr><td><b>-</b></td>
+          <td>Indicates a line in the first file that needs to be deleted.</td>
+          </tr>
+        </table><br>
+
+        After the lines from the first file, there are three dashes ("---"),
+        then a line range, then four dashes ("----"). This indicates the
+        line range in the second file that will sync up with our changes
+        in the first file.<br><br>
+
+        If there is more than one section that needs to change, diff will
+        show these sections one after the other. Lines from the first file will
+        still be indicated with "***", and lines from the second file
+        with "---".
+
+ </li>
+
+  <li><h4> -u</h4>:Unified mode (the -u option) is similar to context mode,
+         but it doesn't display any redundant information. Here's an example,
+         using the same input files as our last example:
+        <pre>diff -u file1.txt file2.txt</pre>
+         will output:<br>
+         <pre> --- file1.txt   2014-08-21 17:58:29.764656635 -0400<br>
++++ file2.txt   2014-08-21 17:58:50.768989841 -0400<br>
+@@ -1,4 +1,4 @@<br>
+ apples<br>
+-oranges<br>
+ kiwis<br>
+ carrots<br>
++grapefruits</pre>
+
+The output is similar to above, but as you can see, the differences are
+ "unified" into one set.