Shell skills

You know the commands. Now learn the tricks that make you fast: repeating yourself without retyping, making your own shortcuts, finding help without Google, keeping work running after you disconnect, and setting a server's clock and name.

History: never type it twice

history              # every command you've run, numbered
history | grep ssh   # "what was that ssh command yesterday?"
!!                   # run the last command again
sudo !!              # run the last command again, WITH sudo
!42                  # run command number 42 from the history list
!cat                 # run the most recent command that started with "cat"

sudo !! is the one everybody learns first. You type a long command, get “Permission denied,” and instead of retyping you just say “that again, but as admin.” Bash prints the expanded command before running it, so you can see what !! became.

Variables and the environment

A variable is a name that holds a value. $ in front of a name means “put the value here.” Some are set for you, and together they're called the environment:

echo $HOME $USER $SHELL     # your home folder, your name, your shell
echo $PATH                  # where bash looks for commands
env                         # the whole environment
PET=cat                     # make a variable (NO spaces around =)
echo "My pet is a $PET"     # double quotes: $ still works
echo 'My pet is a $PET'     # single quotes: printed exactly as typed
export PET                  # share it with programs you start
export EDITOR=nano          # make and export in one go

Want to put a command's output into a variable, like n=$(ls | wc -l)? That's lesson 12. Without export, only your shell can see the variable. With export, every program you start from this shell gets a copy. That's how EDITOR=nano tells crontab -e which editor to open (lesson 5).

Your own shortcuts: alias and ~/.bashrc

alias update='sudo dnf upgrade'
alias                   # list all aliases
type update             # what is "update"?

alias update='sudo apt update && sudo apt upgrade'
alias
type update

Aliases and variables disappear when you log out. To keep them, add the same lines to the end of ~/.bashrc, a hidden settings file that bash runs every time it starts. Run source ~/.bashrc to load it right away. Rocky and Ubuntu start with different ready-made aliases: try alias on each.

Getting help without leaving the terminal

ls --help            # quick summary of the options
man ls               # the full manual. / to search, q to quit
man -k compress      # "which command does…?" Searches every manual's description
apropos compress     # same thing as man -k

--help is fast, and almost every command has it. man is the full manual, and it's the source of truth when an AI or a website invents an option that doesn't exist. man -k helps when you know what you want to do but not the command's name.

watch: rerun a command every few seconds

watch -n 2 df -h                 # refresh disk space every 2 seconds
watch -n 1 'ss -tn | wc -l'      # count connections live (quote pipes!)

Great for watching a copy fill a disk or a service come back up. Press Ctrl+C to stop.

Surviving disconnects: tmux and screen

You start a two-hour upgrade over SSH, your Wi-Fi drops, and the upgrade is killed halfway. Ouch. A terminal multiplexer keeps a session running on the server. You can disconnect (“detach”), go home, reconnect, and pick up exactly where you left off.

sudo dnf install tmux
tmux new -s work       # start a named session
# Ctrl+B then D  = detach
tmux ls                # list sessions
tmux attach -t work    # come back

tmux new -s work       # already installed
# Ctrl+B then D  = detach
tmux ls
tmux attach -t work
screen -S work         # screen is here too
# Ctrl+A then D  = detach
screen -r work

tmux can do much more, like splitting the window into panes (Ctrl+B then %), but detach and attach are the part that saves your work.

Time and name: timedatectl and hostnamectl

date                                         # the current date and time
date +%F                                     # just 2026-09-27: great for file names
timedatectl                                  # time zone and clock sync status
timedatectl list-timezones | grep America
sudo timedatectl set-timezone America/Chicago
hostnamectl                                  # the name, OS and kernel
sudo hostnamectl set-hostname web01          # rename the server

Many admins keep servers on UTC, so logs from servers in different countries line up. A school server in one city is fine on local time. Just pick one and be consistent.

Try it: speed run ⚡

Quick check