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git-svn-id: svn+ssh://atelier.inf.usi.ch/home/bevilj/group-1@181 a672b425-5310-4d7a-af5c-997e18724b81
168 lines
5 KiB
HTML
168 lines
5 KiB
HTML
---
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layout: page
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author: Alessandro Luini
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category-page: advanced
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category-title: Advanced commands
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tags: difference lines diff file separating
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title: diff
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---
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<p> diff analyzes two files and prints the lines that are different.
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Essentially, it outputs a set of instructions for how to change one file to
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make it identical to the second file.</p>
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<h3>How to use</h3>
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<p> To activate the diff command, we must take as parameters two or more
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files that we want to compare and it will give us the output of
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different lines. <br>
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For example let's say we have two files, file1.txt and file2.txt.<br>
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<br> If <b>file1.txt</b> contains the following four lines of text: </p>
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<ol><code><li>I need to buy apples.</li>
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<li>I need to run around the park.</li>
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<li>I need to wash the dog.</li>
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<li>I need to get the car detailed.</li></code></ol>
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<p> ...and <b>file2.txt</b> contains these four lines: </p>
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<ol><code><li> I need to buy apples.</li>
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<li>I need to do the laundry.</li>
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<li>I need to wash the dog.</li>
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<li>I need to get the dog detailed.</li></ol></code>
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<p>...then we can use diff to automatically display for us which lines differ
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between the two files with this command:</p>
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<pre>diff file1.txt file2.txt</pre>
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<p> ...and the output will be:</p>
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<pre> 2,4c2,4 <br>
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< I need to run the laundry.<br>
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< I need to wash the dog.<br>
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< I need to get the car detailed.<br>
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---<br>
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> I need to do the laundry.<br>
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> I need to wash the car.<br>
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> I need to get the dog detailed.</pre>
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<p> In our output above, "2,4c2,4" means: "Lines 2 through 4 in the first
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file need to be changed to match lines 2 through 4 in the second file.</p>
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<h3>Flags</h3>
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<ul>
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<li><h4> -c:</h4> <br>To view differences in context mode, use the -c option.
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For instance, let's say <b>file1.txt</b> and <b>file2.txt</b> contain
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the following:<br><br>
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<table>
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<tr>
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<th> File1.txt </th> <th>File2.txt</th></tr>
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<tr><td> apples </td> <td>apples</td></tr>
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<tr><td>oranges</td> <td>kiwis</td></tr>
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<tr><td>kiwis</td> <td>carrots</td></tr>
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<tr><td>carrots</td> <td>grapefruits</td></tr></table>
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<pre> diff -c file1.txt file2.txt </pre>
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Our output will be like the following:
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<pre> *** file1.txt 2014-08-21 17:58:29.764656635 -0400<br>
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--- file2.txt 2014-08-21 17:58:50.768989841 -0400<br>
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***************<br>
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*** 1,4 ****<br>
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apples<br>
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- oranges<br>
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kiwis<br>
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carrots<br>
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--- 1,4 ----<br>
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apples<br>
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kiwis<br>
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carrots<br>
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+ grapefruits< </pre>
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The first two lines of this output show us information about our "from"
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file (file 1) and our "to" file (file 2). It lists the file name,
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modification date, and modification time of each of our files, one per
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line. The "from" file is indicated by "***", and the "to" file is
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indicated by "---"..<br>
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<br> The line "***************" is just a separator.
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<br><br> The next line has three asterisks ("***") followed by a line
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range from the first file (in this case lines 1 through 4, separated by
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a comma). Then four asterisks ("****").<br>
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<br> Then it shows us the contents of those lines. If the line is unchanged,
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it's prefixed by two spaces. If the line is changed, however, it's prefixed
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by an indicative character and a space. The character meanings are as
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follows:<br><br>
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<table> <tr>
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<th>Character</th>
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<th>Meaning</th></tr>
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<tr> <td> <b>!</b></td>
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<td>Indicates that this line is part of a group of one or more lines that
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needs to change. There is a corresponding group of lines prefixed with
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"!" in the other file's context as well.</td></tr>
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<tr><td><b>+</b></td>
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<td>Indicates a line in the second file that needs to be added to the
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first file.</td></tr>
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<tr><td><b>-</b></td>
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<td>Indicates a line in the first file that needs to be deleted.</td>
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</tr>
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</table><br>
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After the lines from the first file, there are three dashes ("---"),
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then a line range, then four dashes ("----"). This indicates the
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line range in the second file that will sync up with our changes
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in the first file.<br><br>
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If there is more than one section that needs to change, diff will
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show these sections one after the other. Lines from the first file will
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still be indicated with "***", and lines from the second file
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with "---".
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</li>
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<li><h4> -u</h4>:Unified mode (the -u option) is similar to context mode,
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but it doesn't display any redundant information. Here's an example,
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using the same input files as our last example:
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<pre>diff -u file1.txt file2.txt</pre>
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will output:<br>
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<pre> --- file1.txt 2014-08-21 17:58:29.764656635 -0400<br>
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+++ file2.txt 2014-08-21 17:58:50.768989841 -0400<br>
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@@ -1,4 +1,4 @@<br>
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apples<br>
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-oranges<br>
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kiwis<br>
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carrots<br>
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+grapefruits</pre>
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The output is similar to above, but as you can see, the differences are
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"unified" into one set.
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