The ‘cat’ Command Guide

Introduction to the cat Command

The cat (concatenate) command is a staple in Unix and Unix-like operating systems for displaying, concatenating, and writing file contents to the standard output.

Syntax

cat [OPTION]... [FILE]...

• [OPTION]…: Modify the behavior of cat.
• [FILE]…: Files to be processed. Reads from stdin if no file or - is specified.

Common Options

• -n, --number: Number all output lines.
• -b, --number-nonblank: Number non-empty output lines only.
• -s, --squeeze-blank: Squeeze multiple adjacent blank lines.
• -E, --show-ends: Display $ at the end of each line.
• -T, --show-tabs: Display TAB characters as ^I.

Displaying File Contents

To display the contents of a file:

cat file.txt

Concatenating Files

To concatenate multiple files into one:

cat file1.txt file2.txt > combined.txt

Creating Files

To create a new file:

cat > newfile.txt

Appending to Files

To append text to an existing file:

cat >> existingfile.txt

Viewing Non-Printing Characters

To view end-of-line or tabs:

cat -E file.txt
cat -T file.txt

Reading Standard Input

You can use cat without specifying a file to read from the standard input. This is useful for quickly creating file content from terminal input:

cat > example.txt
Type your content here...
Press CTRL+D (EOF) to save and exit.

Viewing Multiple Files

cat can also be used to view the contents of multiple files sequentially on the terminal. This is a quick way to compare or merge files manually:

cat file1.txt file2.txt file3.txt

Sort and Remove Duplicate Lines

If you have a file with list items or entries that you want to sort and remove duplicates from, you can use cat in combination with other commands like sort and uniq.

cat list.txt | sort | uniq > sorted_list.txt

Using cat list.txt | sort | uniq > sorted_list.txt streamlines the process of organizing data by automatically sorting the contents of list.txt, removing any duplicate entries, and saving the cleaned, ordered list to sorted_list.txt. This command sequence accelerates workflows by performing data cleanup and organization in a single step, eliminating the need for manual sorting and deduplication, thus saving time and reducing potential for error in data handling.

Conclusion

The cat command is an essential tool for text processing in Unix/Linux environments, offering a wide range of functionalities from file display to concatenation and debugging.

Reference

https://www.geeksforgeeks.org/cat-command-in-linux-with-examples/