2.The command line

The Linux/Unix command line is something one has to learn in order to do computational chemistry and can actually be very beneficial in scientific work. Many scientific programs are exclusively written for Linux/Unix and are purely command-line (no graphical user interface).

Only by learning the command line can one use ORCA or other quantum chemistry programs for actual scientific work. These programs run almost exclusively in a Linux/Unix command-line environment and practically all scientific computing clusters run Linux.

You do not have to have a Linux/Unix machine to use command-line programs like ORCA, however. You just need access to a computing cluster and then use an SSH client to access the cluster on your Windows/Mac machine. See Setting up programs.

Quick command-line tutorial

A tutorial on using the command line will eventually be written.

Until then, it's recommended to read one of many guides and tutorials that are available online:

https://www.codecademy.com/courses/learn-the-command-line

http://linuxcommand.org/lc3_learning_the_shell.php

http://www.ee.surrey.ac.uk/Teaching/Unix/

http://cli.learncodethehardway.org/book/

http://lifehacker.com/5633909/who-needs-a-mouse-learn-to-use-the-command-line-for-almost-anything

A figure with the most common commands is shown on the right (click for a larger version).

Command-line text editors

To quickly edit ORCA inputfiles on the cluster, it is recommended to learn to use a command line text editor.

This is much quicker than editing an inputfile using a GUI editor (like Notepad or Textedit).

nano the simplest texteditor. Recommended. A simple guide to nano is here.

vim

emacs

vim and emacs are very popular editors among programmers and some people enjoy endless fights about which one is better.