[Linux] C Shell (csh) uniq Uso: Remove duplicate lines from sorted files

Overview

The uniq command in C Shell (csh) is used to filter out repeated lines in a sorted file. It reads the input and outputs only the unique lines, making it useful for data processing and analysis.

Usage

The basic syntax of the uniq command is as follows:

uniq [options] [arguments]

Common Options

• -c: Prefix each line with the number of occurrences.
• -d: Only print duplicate lines.
• -u: Only print unique lines (lines that are not repeated).
• -i: Ignore case when comparing lines.

Common Examples

Here are some practical examples of how to use the uniq command:

1. Basic usage: Remove duplicates from a sorted file.

   uniq sorted_file.txt
   

2. Count occurrences: Show how many times each line appears.

   uniq -c sorted_file.txt
   

3. Show only duplicates: Display lines that appear more than once.

   uniq -d sorted_file.txt
   

4. Show only unique lines: Display lines that are not repeated.

   uniq -u sorted_file.txt
   

5. Ignore case: Remove duplicates while ignoring case sensitivity.

   uniq -i sorted_file.txt
   

Tips

• Always sort your input file before using uniq, as it only removes adjacent duplicate lines.
• Use the -c option to quickly identify how many times each line appears, which can be helpful for data analysis.
• Combine uniq with other commands like sort to enhance its functionality, for example:

  sort unsorted_file.txt | uniq
  

• Remember that uniq processes input from standard input as well, so you can pipe data directly into it.