Viewing Files

You've created files, moved them around, and cleaned up. Now you need to look inside them. Unix offers several commands for viewing file contents, each suited to a different situation.

cat — quick peek

cat (short for concatenate) prints the entire file to the terminal. It's perfect for short files.

$ cat notes.txt
Buy groceries
Finish project
Call mom
    

For anything longer than a screen or two, cat becomes unwieldy — the text scrolls past and you can't read it all.

less — scroll and search

less shows you a file one screen at a time. You can scroll up and down and even search.

$ less longfile.txt
    

Once inside less:

• Space or f — forward one page
• b — back one page
• /searchterm — search for text
• q — quit

The name "less" is a joke from the old days — it's a better version of more, which only let you scroll forward. Less really is more.

head and tail — just the edges

head shows the first 10 lines of a file. tail shows the last 10 lines.

$ head -n 20 data.csv
$ tail -n 5 app.log
    

Use -n to specify a different number of lines. head -n 100 shows the first 100 lines.

tail -f — watch logs live

This is one of those Unix commands you'll fall in love with. tail -f follows a file as it grows — new lines appear on screen as they're written.

$ tail -f /var/log/syslog
    

It's perfect for watching log files in real time. Press Ctrl+C to stop following. Every developer and sysadmin uses this daily — it's how you see what your application is doing right now.

Which one to use?

• cat — short files, quick checks, or piping to another command
• less — long files you need to explore
• head / tail — when you only need the beginning or end
• tail -f — watching logs or any live-updating file