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A Short Introduction to the Linux Command Line

During the Tutorial Annif will mainly be controlled from Linux command line. This document provides an overview of the functionalities used. You can return to the examples in this document to better understand the commands used during the tutorial. You get access to the command line by opening the Terminal application.

Directories

Files in Linux are organized in a hiearchy of directories. You can navigate through the hierarchy from the command line. This is similar to clicking through folders in a graphical file explorer (i.e., Windows Explorer or Finder on Mac OS).

The Current Directory

Commands are usually executed relative to a directory. To show the current directory the pwd command can be used.

pwd

Contents of a Directory

The ls command, shorthand for list, lists the contents of the directory.

ls

You can modify the output of the directory listing with arguments. The option -l prints each item on a new line.

ls -l

Changing a Directory

You can switch a directory using the change directory (cd) command.

pwd
cd folder
pwd

There are some special arguments to cd:

  • cd .. will navigate to the parent directory, i.e., the directory containing the current one.
  • cd without an argument will navigate to a users home folder. This is where your personal files and configurations are located.
  • cd - Will go to the directory you previously used.

Absolute Paths

The previous examples used relative paths as the argument to cd. I.e., they were either a subdirectory of the current directory or its parent. You can also use absolute paths that refrence the root of the file hierarchy. These are called absolute paths and start with a /.

Output Redirection

Some of the programs used during the tutorial will print output to the terminal. After the programs have terminated it is hard to use the output in other programs. However it is possible to write the output of a program to a file. This is done using the redirection operators:

  • cmd_1 > itermediate.txt will write the output of the command cmd_1 to a file called intermediate.txt
  • cmd_2 < intermediate.txt will use the contents of the file intermediate.txt as input to command cmd_2

It is also possible to skip the intermediate file. When running cmd_1 | cmd_2 the output of cmd_1 is used as input to cmd_2.

Text Editor Nano

There are many different text editors for the commandline. If you are new to the command line, nano is an easy to use choice.

Open a File

You can give an editor program the file you want to edit as an argument.

nano projects.cfg will open the file projects.cfg in the current directory for editing. If it does not exist it, will be created.

Saving changes

In nano pressing ctrl and the o key at the same time saves the modifications you made. The program will ask for the location where the file should be saved. If you want to apply the changes to the existing file, hit enter.

Exiting Nano

Pressing ctrl and the x key at the same time will close nano. If you have unsafed modifications to the file you are editing, nano will prompt you to save the changes. You can answer the prompt by pressing the y or n key.