cat prints a whole file. It's quickest for short files; for a long one the start scrolls away before you can read it.
less opens a file one screen at a time. Use the arrow keys or Space to move, / and a word to search, n for the next match, and q to quit. Many commands, like man, show their pages in less, so the same keys work there.
head shows the first 10 lines and tail the last 10. -n picks how many: head -n 3 list.txt. tail -f (follow) keeps printing new lines as they're added, which is how you watch a log file while something runs. Press Ctrl+C to stop.
$ cat ducks.txt
mallard
teal
pintail
eider
$ head -n 2 ducks.txt
mallard
teal
$ wc -l ducks.txt
4 ducks.txtwc (word count) counts lines, words and bytes. wc -l counts just lines, which is handy for "how many entries are in this list?"
Text files are the heart of Linux: settings, logs and scripts are all plain text, so these few commands let you look at almost anything on the system.
Print the last 10 lines of app.log.
| cat file | Print the whole file. |
|---|---|
| less file | Read page by page. `/` search, `n` next, `q` quit. |
| head -n N, tail -n N | First or last N lines (10 by default). |
| tail -f file | Keep showing new lines. Ctrl+C stops. |
| wc -l file | Count lines. |