cat

Additional Notes

cat prints file contents to standard output. The name comes from concatenate because it can join multiple files together.

It is best for short files, quick checks, and combining files. For long files, use less, more, head, or tail so the output does not flood the terminal.

Syntax

cat [options] [file...]

Parameters

• file: One or more files to print.
• No file: Reads from standard input.

Common Options

• -n, --number: Number all output lines.
• -b, --number-nonblank: Number only non-empty lines.
• -s, --squeeze-blank: Replace repeated blank lines with one blank line.
• -A, --show-all: Show tabs, line endings, and non-printing characters.
• -T, --show-tabs: Show tab characters as ^I.
• -E, --show-ends: Show line endings as $.

Examples

cat file.txt

Print a file.

cat -n script.sh

Print a file with line numbers.

cat part1.txt part2.txt > combined.txt

Join two files into a new file.

cat >> notes.txt

Append typed input to a file. Press Ctrl+D to finish.

cat -A file.txt

Reveal hidden characters such as tabs and line endings.

Practical Notes

• cat file > other overwrites other; cat file >> other appends.
• Avoid using cat file | grep pattern when grep pattern file is enough.
• Use less file for long files.
• Use head and tail to inspect only the beginning or end of a file.