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The //**uniq**// command in Linux and Unix-like systems is used to filter out the duplicate lines from a sorted file. It compares the adjacent lines and removes the duplicate lines, preserving only one copy of the duplicated lines.

Here is the basic syntax for the **uniq** command:

<code>
uniq [options] [file]</code>
file is the name of the file you want to filter out the duplicate lines.
Here are some examples of the uniq command in action:

1. To filter out the duplicate lines from a file called "file1.txt"
<code>
$ sort file1.txt | uniq</code>
Note: The sort command is used to sort the lines of a file before running the uniq command, as the uniq command only works on sorted input.

2. To display the count of the occurrences of each line
<code>
$ sort file1.txt | uniq -c</code>
Note: The **-c** option is used to display the count of the occurrences of each line.

3. To ignore the case when comparing lines
<code>
$ sort -f file1.txt | uniq</code>
Note: The **-f** option is used to ignore the case when comparing lines.  In other words, **sort -f** will convert all lowercase characters to their uppercase equivalent before comparison, that is, perform case-independent sorting before running the **uniq** command.

4. To only display the unique lines
<code>
$ sort file1.txt | uniq -u</code>
Note: The **-u** option is used to only display the unique lines

5. To only display the duplicate lines
<code>
$ sort file1.txt | uniq -d</code>
Note: The **-d** option is used to only display the duplicate lines

The **uniq** command is useful for filtering out the duplicate lines from a sorted file, it compares the adjacent lines and removes the duplicate lines, preserving only one copy of the duplicated lines. This command can be useful when you have a large file and you want to identify and remove duplicate lines, for example when you are working on a data-cleaning task. Additionally, the **uniq** command can be used in conjunction with other commands like [[unix_commands:sort|sort]] and [[unix_commands:grep|grep]] to further filter and manipulate the output of the command. It can also be used to count the number of occurrences of each line in a file, which can be useful for analyzing data or for troubleshooting purposes.
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