less — page through files interactively

What it does

less displays the contents of a file one screenful at a time, letting you scroll forward and backward, search, and jump around without ever dumping the whole thing into your terminal. It replaces the older more, and its name is a pun: "less" is "more, backwards". Because it pages instead of printing everything, less is the right tool for reading logs, long configs, and command output that would otherwise fly past.

Why it matters

less is the safety net for the Unix pipeline. Pipe anything too long into it — man, git log, or any command's output — and you get an interactive viewer instead of a wall of scrolling text. Unlike cat, which vomits the entire file at once, less leaves your screen intact and remembers where you left off (with -R it even handles colorized output). Once you learn its keys — space to page, / to search, q to quit — you will reach for it constantly.

Example

$ less -N /var/log/syslog

    1 Aug 21 08:00:01 host systemd[1]: Starting Daily apt upgrade and clean activities
    2 Aug 21 08:00:03 host kernel: [  123.456] usb 1-1: new high-speed USB device
    3 Aug 21 08:00:05 host sshd[1042]: Accepted publickey for kmail from 10.0.0.5
    4 Aug 21 08:00:07 host systemd[1]: Started Daily apt upgrade and clean activities
    :

$ ps aux | less

USER       PID %CPU %MEM    VSZ   RSS TTY  STAT START   TIME COMMAND
root         1  0.0  0.1  168912 13768 ?    Ss   08:00   0:01 /sbin/init
root       245  0.1  0.2 1691200 23892 ?    Sl   08:00   0:00 /usr/lib/systemd/systemd
kmail     1890  0.3  0.3 1054520 36552   ?    Sl   08:01   0:02 /usr/bin/kitty
...
(END)

Common flags

-N

show line numbers in the left margin

-R

render ANSI color codes instead of showing them as junk

-S

chop (don't wrap) long lines; scroll sideways with arrows

-i

ignore case during searches

-G

only highlight the currently matching search term

-F

quit if the file fits on one screen (like cat when short)

-X

leave the file's content on screen after quitting