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cat Tool Reference

cat (concatenate) displays file contents to stdout. One of the most fundamental Unix commands for reading files, combining files, and creating files.

Basic Usage

  • cat file.txt - Display file contents
  • cat file1.txt file2.txt - Concatenate multiple files
  • cat file.txt | less - Pipe to pager
  • cat > newfile.txt - Create file (Ctrl+D to finish)
  • cat >> file.txt - Append to file

Options

  • -n - Number all output lines
  • -b - Number non-blank lines
  • -s - Squeeze blank lines
  • -E - Show end of line with $
  • -T - Show tabs as ^I
  • -v - Show non-printing characters
  • -A - Equivalent to -vET

Common Examples

Display File

cat file.txt

Show file contents.

Number Lines

cat -n file.txt

Display with line numbers.

Create File

cat > newfile.txt
(type content)
Ctrl+D

Create new file from stdin.

Append to File

cat >> file.txt
(type content)
Ctrl+D

Append content to file.

Concatenate Files

cat file1.txt file2.txt > combined.txt

Combine multiple files.

Show Non-Printing

cat -A file.txt

Show all characters including tabs and line endings.

Pipe to Other Commands

cat file.txt | grep pattern

Use cat in pipelines.

Tips

  • Use -n to number lines for reference
  • Use -A to debug file formatting issues
  • Use > to create, >> to append
  • Essential for file inspection
  • Works great in pipelines
  • Use less or more for large files
  • One of the most basic Unix commands
  • Perfect for quick file viewing