LINUX COMMAND LINE

The list below provides basic commands for performing tasks from a Linux terminal, but it is by no means exhaustive. You can find many great command line tutorials on the web, for example:

• Ubuntu command line for beginners

• Linux commands cheat sheet

• linuxcommand.org

• Software carpentry shell tutorial

• UNIX Tutorial for Beginners

Navigating directories

• pwd print working directory, i.e., the current directory

• ls list files in the working directory.

• ls -l list files in long format, i.e., with extra information.

• ls -a list all files, i.e., including hidden files whose filenames being with .

• ls -la list all files in long format

• ls ~/Documents/ list files in the ~/Documents/ directory

  • Note that ~ is the home directory of the logged in user

  • For example, if logged in as myrobot, then ~ is /home/myrobot

• man ls display the the manual entry for the ls command.

• cd ~/Documents change directory to ~/Documents

• cd .. change directory up one level

Editing filenames and directories

• cp myscript.py myscript_new.py make a copy of the file myscript.py named myscript_new.py in the current directory

• mkdir oldscripts make a new directory named oldscripts

• mv myscript.py oldscripts/myscript_old.py move the file myscript.py into the directory oldscripts and at the same time rename it to myscript_old.py

• cp hello.py oldscripts/hello_old.py copy the file hello.py into the directory oldscripts and at the same time rename it to hello_old.py

• cp -r oldscripts/ unused copy the directory oldscripts and all its contents recursively into a new directory named unused, the directory unused is created if it does not already exist

• rm hello.py remove the file hello.py

  • Note that rm is permanent and cannot be undone, less the file is tracked using a git repository

• rm -r oldscripts remove recursively the directory oldscripts and all its contents

• rmdir oldscripts remove oldscripts only if it is an empty directory

Displaying files

• cat .bashrc prints the whole contents of the file named .bashrc to the screen

• less .bashrc an interactive way to view files, especially useful for long filenames

  • Note the manual entry, i.e., man less, details the navigation shortcuts, some of the most useful are as follows.

  • d and u to scroll down and up by half a window respectively

  • f and b to scroll forwards and backwards by a one window respectively

  • g and G scroll to the beginning and end of the file respectively

  • /pattern then press ENTER to search forward in the file for occurrences of pattern

    • n and N to repeat the search in the forward and backward direction respectively

    • All matches of pattern are highlighted

  • q to quit and return to the command line prompt

Editing files

• nano myscript.py edit the file myscript.py using the nano program

• vi myscript.py edit the file myscript.py using the vi program

• Note the nano editor is more similar to editing with a GUI based text editor and it displays the key commands on the screen. The vi editor is more powerful but has a steeper learning curve for internalising its commands.

Executing files

• python myscript.py executes the python file myscript.py

• chmod +x myscript.py make the file myscript.py executable

  • Note the command chmod is used for modifying file permissions, see man chmod

  • Note see this tutorial on using chmod for more details

• ./hello.py run the executable file named myscript.py

Installing programs

• sudo apt install figlet install the figlet program

• figlet ASClinic run the figlet program with the argument ASClinc, which prints out the following:

    _    ____   ____ _ _       _
   / \  / ___| / ___| (_)____ (_) ___
  / _ \ \___ \| |   | | |  _ \| |/ __|
 / ___ \ ___) | |___| | | | | | | (__
/_/   \_\____/ \____|_|_|_| |_|_|\___|

• sudo apt install install the tree program

• tree run the tree program to display the file structure of the working directory

Secure shell and secure copying

• ssh username@ip_address log in as username to a terminal on the remote machine at ip_address, .i.e., log in to a secure shell

• scp myscript.py username@ip_address:Documents copy the file myscript.py from your local machine to the remote machine at ip_address into the Documents sub-folder of username’s home directory

  • Note see this tutorial on using scp for more details

Mosh - mobile shell connection

• mosh username@ip_address log in as username to a terminal on the remote machine at ip_address using mosh, which stands for mobile shell.

  • If you are using ssh in areas of your campus with patchy WiFi connection, then a frequent occurrence of broken ssh pipelines can be frustrating. As described on the mosh website, mosh is a “remote terminal application that allows roaming and supports intermittent connectivity”, and hence is ideal for such situations where the WiFi connection is patchy.

  • To use mosh, it needs to be installed on both the robot (see Install mosh) and your personal computer.

Miscellaneous

• Ctrl-C stop the currently active command, useful for when you get stuck