Command Line Basics

Basic Linux command line notes.

This page explains common commands and how to move around the terminal.

What is the command line?

The command line is where you type commands to interact with the system.

Example:

ls

The shell reads the command and runs it.

Show current directory

pwd

pwd means:

print working directory

Example output:

/home/user

List files

ls

List with details:

ls -l

List hidden files too:

ls -la

Human-readable sizes:

ls -lah

Change directory

cd /path/to/directory

Go to home directory:

cd

Go one directory up:

cd ..

Go to previous directory:

cd -

Create directory

mkdir DIRECTORY_NAME

Create parent directories if needed:

mkdir -p /path/to/directory

Create empty file

touch file.txt

Copy files

cp source.txt destination.txt

Copy directory recursively:

cp -r source_directory destination_directory

Move or rename files

Move file:

mv file.txt /tmp/file.txt

Rename file:

mv oldname.txt newname.txt

Remove files

rm file.txt

Remove directory and contents:

rm -r directory

Force remove:

rm -rf directory

Be very careful with rm -rf.

View file content

Show full file:

cat file.txt

Show one page at a time:

less file.txt

Show first lines:

head file.txt

Show last lines:

tail file.txt

Show last 100 lines:

tail -n 100 file.txt

Follow file live:

tail -f file.txt

Search text in files

Search in one file:

grep "text" file.txt

Case-insensitive:

grep -i "text" file.txt

Search recursively:

grep -R "text" /path

Show line numbers:

grep -n "text" file.txt

Find files

Find by name:

find /path -name "filename"

Example:

find /etc -name "*.conf"

Find directories:

find /path -type d -name "directory_name"

Find files:

find /path -type f -name "*.log"

Command history

Show command history:

history

Search history:

history | grep "text"

Repeat previous command:

!!

Run previous command with sudo:

sudo !!

Pipes

A pipe sends output from one command into another command.

Example:

ps aux | grep ssh

This means:

show processes
send output to grep
filter lines containing ssh

Redirect output

Save output to a file:

command > file.txt

Append output to a file:

command >> file.txt

Redirect errors too:

command > file.txt 2>&1

Useful shortcuts

Ctrl + C = stop current command
Ctrl + L = clear screen
Ctrl + R = search command history
Tab      = autocomplete
Up Arrow = previous command

Check command location

which COMMAND

Example:

which ssh

More detail:

type COMMAND

Example:

type cd

Manual pages

Open manual page:

man COMMAND

Example:

man ls

Search inside man:

/type_search_here

Quit:

Help option

Many commands support:

COMMAND --help

Example:

ls --help

Common first commands

pwd
ls -lah
cd /path
cat file.txt
less file.txt
tail -n 100 file.txt
grep "error" file.txt
find /path -name "file"
history

Dangerous commands

Be careful with:

rm -rf
chmod -R
chown -R
dd
mkfs
wipefs
fdisk
parted
reboot
shutdown
systemctl restart

Always check the path before running destructive commands.