The terminal for beginners: everyday commands

Why you can't avoid it

A server has no windows and no mouse. There's only a text prompt.

Besides, many developer tools are driven only from there: version control, package installation, builds, running tests. Someone afraid of the terminal spends several times longer on simple things.

The good news: twenty commands cover ninety per cent of tasks.

Moving around and looking

pwd              where am I
ls               what's here
ls -la           in detail, including hidden files
cd folder        go into it
cd ..            up one level
cd ~             home

Files and folders

mkdir name       create a folder
mkdir -p a/b/c   create nested folders at once
touch file       create an empty file
cp what where    copy
cp -r folder where copy a folder entirely
mv what where    move or rename
rm file          delete
rm -r folder     delete a folder

About deletion: the command asks no confirmation and uses no wastebasket. What's deleted is gone. Before pressing enter on a delete with a wildcard, look with your eyes at exactly what you're deleting.

Viewing contents

cat file             show it all
head -20 file        first 20 lines
tail -20 file        last 20 lines
tail -f file         follow as it's written
less file            page through (q to quit)

Following a file as it's written is the main tool when investigating a running server.

Searching

grep "text" file           find lines containing text
grep -r "text" .           search every file in a folder
grep -i "text" file        case-insensitive
find . -name "*.py"        find files by name

Searching file contents is a daily activity. Learn it properly.

Processes and the system

ps aux | grep python   which processes are running
kill number            stop a process
df -h                  disk space
du -sh folder          how much a folder occupies
top                    what's loading the system

Checking disk space saves you regularly: a disk filled by logs is a classic cause of sudden failure.

Chaining commands

The terminal's main strength is passing one command's output into another:

cat app.log | grep ERROR | tail -20

Read as: take the file, keep the error lines, show the last twenty.

Redirecting into a file:

command > file       write, overwriting
command >> file      append

Time-saving habits

The completion key. Start typing a filename and press it — it completes. Not a luxury but a way to avoid mistyping paths.

The up arrow. Previous commands. Don't retype.

History search. The reverse-search shortcut finds a command you typed a week ago.

Interrupt. The shortcut that stops the current command is the first thing to memorise, so you aren't afraid to run anything.

What not to do

Don't run commands from the internet without understanding them. Especially with elevated privileges. A line that downloads a script and immediately runs it as administrator is the standard way to hand your machine to someone else.

Don't delete recursively from the root. The classic catastrophe. Always check where you are before deleting.

Don't work as administrator all the time. Elevate only where it's genuinely needed.