Linux Command Line Basics: A Concise Primer for New Devs

If you're going to build software on a server, you'll live in the terminal. Here are the commands that cover most of what you'll do, explained plainly.

1Where am I? What's here?

pwd              # print working directory (where I am)
ls               # list files in this directory
ls -la           # long format, including hidden files (those starting with .)
cd <dir>         # change directory
cd ..            # go up one level
cd ~             # go to my home directory

~ is a shortcut for your home. . is the current directory, .. the parent.

2Reading and creating files

cat file.txt        # print a file's contents
head -20 file.txt   # first 20 lines
tail -20 file.txt   # last 20 lines
less file.txt       # scroll through a file (q to quit)
touch newfile.txt   # create an empty file (or update its timestamp)
nano file.txt       # edit a file in a simple editor (Ctrl+O save, Ctrl+X exit)

To see line numbers while reading: cat -n file.txt.

3Moving, copying, removing

cp source.txt dest.txt     # copy
mv old.txt new.txt         # move or rename
rm file.txt                # remove a file
rm -r directory/           # remove a directory and its contents
mkdir newdir               # make a directory

rm -r is dangerous — it deletes recursively and permanently. There's no undo. rm -rf / would delete everything; never type that casually.

4Searching inside files

grep finds lines matching text:

grep "error" server.log          # lines containing "error"
grep -i "error" server.log       # case-insensitive
grep -rn "config" /etc/nginx/    # recursive search across files with line numbers

5Piping: combining commands

The pipe | sends one command's output into the next:

ls -la | grep nginx        # list, then filter to lines mentioning nginx
cat server.log | tail -50  # all lines, then keep the last 50
history | grep docker      # find a command you ran before

This is the shell's superpower — small commands combined to do big things.

6Permissions

Every file has a user and a group, with read/write/execute rights for each:

ls -l file.txt          # shows permissions like -rw-r--r--
chmod +x script.sh      # make a script executable
chmod 600 secrets.json  # owner read/write only (good for secrets)
chown user:group file   # change owner/group

A quick mental map: chmod 600 = owner can read+write, everyone else nothing (for secrets). chmod 755 = owner full, others read+execute (for programs/directories).

7Processes and resources

top                # live view of CPU/memory by process
ps aux | grep nginx # find a running process
kill <pid>         # end a process by ID
df -h              # disk space
free -h            # memory

On a small server, free -h and df -h are your first stops when something feels slow.

8Superuser

On Ubuntu, sudo runs a command as root:

sudo apt update          # package manager refresh (needs privileges)

sudo is powerful — only use it when a command genuinely needs it, and always double-check the command.

The habit that beats memorizing

You don't need to memorise everything. man <command> opens a command's manual (man ls, man grep), and command --help shows a summary. When stuck:

somecommand --help

That, plus the pipe, plus grep, covers a surprising amount of real work. Everything else you look up as you go.