cat Command Guide: View and Concatenate File Contents

cat Overview

`cat` is one of the most basic commands in Linux/Unix systems, useful for quickly checking the content of text files or combining the content of multiple files to create a new one. Be careful when outputting binary files with `cat`, as unknown characters may be displayed on the terminal.

Main Roles of cat

The `cat` command is primarily used for the following purposes:

Key Application Areas

Viewing File Content: Outputs the entire content of a text file to the terminal.
Concatenating Files: Combines the content of multiple files in order to create a single output or save it to a new file.
Creating New Files: Creates a new file by directly inputting content via standard input.
Simple Pipeline Construction: Used to pass file content as input to other commands.

Main cat Command Options

The `cat` command is simple, but it can control the output format through several useful options.

1. Basic Output Option

2. Formatting Options

Generated command:

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Description:

`cat` Executes the command.

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Usage Examples

Learn how to view file content, concatenate files, and create new files through various usage examples of the `cat` command.

Output Single File Content

cat my_file.txt

Displays the entire content of `my_file.txt` to the terminal.

Concatenate and Output Multiple Files

cat file1.txt file2.txt file3.txt

Combines the contents of `file1.txt`, `file2.txt`, and `file3.txt` in order and outputs them to the terminal.

Concatenate Multiple Files and Save to New File

cat file1.txt file2.txt > combined.txt

Combines the contents of `file1.txt` and `file2.txt` and saves them to a new file named `combined.txt`. If `combined.txt` already exists, it will be overwritten.

Output File Content with Line Numbers

cat -n document.txt

Outputs each line of `document.txt` prefixed with line numbers.

Create New File (using Standard Input)

cat > new_file.txt
# Type your content here
# Press Ctrl+D to save and exit

Creates `new_file.txt` and saves content directly typed into the terminal to the file. Press `Ctrl+D` to save and exit when done typing.

Real-time Log File Monitoring (used with tail)

cat /var/log/syslog | grep -i error

While `tail -f` is generally more suitable for real-time log file monitoring, `cat` can also be used in pipelines. This example shows a simple case of `cat` piping log file content to `grep`.