Linux and terminal basics

The terminal is a text-based way to interact with the computer. ROS 2 development uses terminals to navigate directories, build workspaces, source environments, and start nodes.

Essential commands

Show the current directory

pwd

List files and directories

ls
ls -l

ls -l also displays permissions, ownership, size, and modification time.

Change directory

cd ~/ros2_workshop
cd ..
cd -

  • .. is the parent directory.

  • ~ is your home directory.

  • cd - returns to the previous directory.

Create directories

mkdir my_directory
mkdir -p dev_ws/src

The -p option creates missing parent directories.

Copy and move files

cp source.txt destination.txt
mv old_name.txt new_name.txt

mv can rename a file or move it into another directory.

Create and inspect files

touch notes.txt
less notes.txt

Press q to leave less.

Permissions and scripts

The permission string shown by ls -l may look like:

-rw-rw-r-- 1 user user 29 Apr 13 10:00 hello_world.sh

The three permission groups apply to the owner, group, and others:

  • r: read

  • w: write

  • x: execute

  • -: permission not granted

Make a script executable and run it:

chmod +x hello_world.sh
./hello_world.sh

A script can also be passed directly to Bash:

bash hello_world.sh

Using sudo safely

sudo runs a command with administrator privileges. It is normally needed for system-wide actions such as installing packages:

sudo apt update

Do not use sudo for ordinary work in your home directory. A mistaken administrator command can modify or damage the system.

Useful terminal features

  • Press Tab to complete command and file names.

  • Press the up and down arrows to browse command history.

  • Press Ctrl+C to interrupt a running foreground command.

  • Use clear or press Ctrl+L to clear the terminal display.

  • Run pwd when you are uncertain about the current directory.

Exercise

  1. Create ~/ros2_workshop/linux_exercise.

  2. Inside it, create the directories source and workspace/src.

  3. In source, create hello_world.sh with this content:

    #!/usr/bin/env bash

echo "Hello world"

  4. Copy the script into workspace/src.

  5. Make the copied script executable.

  6. Run it from workspace/src.

Solution

mkdir -p ~/ros2_workshop/linux_exercise/source
mkdir -p ~/ros2_workshop/linux_exercise/workspace/src
cd ~/ros2_workshop/linux_exercise/source
nano hello_world.sh
cp hello_world.sh ../workspace/src/
cd ../workspace/src
chmod +x hello_world.sh
./hello_world.sh

Expected output:

Hello world