How do you view the contents of a file?

Several commands display file contents. cat filename prints the entire file. less filename shows it page by page (press q to quit, / to search) — preferred for large files. more filename is an older pager. head -n 20 filename shows the first 20 lines. tail -n 20 filename shows the last 20 lines. tail -f filename follows the file in real time — essential for log monitoring. tac filename prints lines in reverse order.