Viewing File Contents (cat)

The cat command displays file contents. It's the simplest way to view what's inside a file.

Basic Usage

cat filename

What cat Does

cat stands for "concatenate" - it can:

1. Display file contents
2. Combine multiple files
3. Create new files
4. Number lines

cat Options

Option	Description
-n	Number all lines
-b	Number non-blank lines only
-s	Squeeze multiple blank lines
-A	Show all (including hidden characters)
-E	Show $ at end of lines

Viewing Multiple Files

Concatenate and display multiple files:

cat file1.txt file2.txt
cat *.txt

Exercise: View a File

Display the contents of the notes.txt file:

Creating Files with cat

Using Redirection

cat > newfile.txt
Type your content here
Press Ctrl+D to save

Using Heredoc

cat > script.sh << 'EOF'
#!/bin/bash
echo "Hello World"
EOF

Combining Files

cat header.txt body.txt footer.txt > complete.txt
cat part1.txt part2.txt >> combined.txt  # Append

When NOT to Use cat

For large files, use:

• less - for paging
• head - for first lines
• tail - for last lines

# Avoid for large files:
cat huge_log.txt        # Floods terminal

# Better alternatives:
less huge_log.txt       # Page through
head huge_log.txt       # First 10 lines
tail huge_log.txt       # Last 10 lines

Numbered Output

cat -n file.txt         # Number all lines
cat -b file.txt         # Number non-blank lines

Useful Patterns

Quick File Preview

cat /etc/hostname       # Check hostname
cat /etc/hosts          # Check hosts file
cat ~/.bashrc           # View bash config

Check File Type

cat -A file.txt         # Shows hidden chars
                        # Useful for debugging

Key Takeaways

• cat displays file contents
• Use -n to number lines
• Can combine multiple files
• For large files, use less, head, or tail
• cat is for quick viewing of small files