cat Command Guide

Basic Usage

The simplest use of cat is to display the contents of a file.

cat filename.txt

You can display multiple files at once:

cat file1.txt file2.txt file3.txt

Common Options

Show line numbers (-n)

cat -n filename.txt

Number non-empty lines (-b)

cat -b filename.txt

Show non-printing characters (-v)

cat -v filename.txt

Show tabs and end of lines (-A)

cat -A filename.txt

Concatenating Files

The original purpose of cat is to concatenate (combine) files.

Combine files into one

cat file1.txt file2.txt > combined.txt

Append to a file

cat newcontent.txt >> existing.txt

Creating Files

Create a file from input

cat > newfile.txt
Type your content here
Press Ctrl+D when done

Create a file with heredoc

cat << EOF > config.txt
line 1
line 2
line 3
EOF

Practical Examples

View a configuration file

cat /etc/hosts

Display with line numbers for debugging

cat -n script.sh

Combine multiple log files

cat access.log.1 access.log.2 access.log.3 > combined.log

Pipe to other commands

# Count lines
cat file.txt | wc -l

# Search content
cat file.txt | grep "pattern"

# View with pagination
cat file.txt | less

Display file in reverse (tac)

tac file.txt

Alternatives to cat

For large files or specific use cases, consider these alternatives:

# View beginning of a file
head -n 20 file.txt

# View end of a file
tail -n 20 file.txt

# View with pagination
less file.txt

# View with syntax highlighting
bat file.txt  # if installed

Summary

The cat command is versatile for viewing and combining files. Key takeaways:

• Use cat file to display file contents
• Use cat -n to show line numbers
• Use cat file1 file2 > combined to merge files
• Use >> to append instead of overwrite
• Consider less or head/tail for large files