Using the Terminal for Doing Stuff

People working a lot with MAC or Linux systems might be used to doing things from the terminal or console. For novices, it usually appears more frightening than it actually is. Especially when working on remote servers - but also for embedded devices for audio processing - the terminal is the standard tool.


Directories

You can maneuver through the system's directories using the cd command. Changing to an absolute path /foo/bar can be done like this:

$ cd /foo/bar

New directories are created with the mkdir command. For creating a new directory mydir in your recent location, type:

$ mkdir mydir

The content of the recent directory can be listed with the ls command. The following arguments improve the results:

$ ls -lah

drwxrwxr-x  2 username group 4,0K Mar 25 12:25 .
drwxrwxr-x 16 username group 4,0K Mar 25 12:25 ..
-rwxrwxr-x  1 username group 9,1M Feb  3 17:47 jacktrip
-rwxrwxr-x  1 username group 334K Feb  3 17:47 sprawl-compositor

Exercise

Create a directory with your name in the student user home directory /home/student/students/YOURNAME.


Create and Edit Files

A file can be created by touching it:

$ touch filename

The default editor on most systems is nano. It is a minimal terminal based tool and does not require X forwarding. To edit an existing file or create a new file, type:

$ nano filename

Terminal Only

Inside nano, you have a lot of defined keystrokes for editing, file handling and other tasks. See the nano cheat sheet for a full list: https://www.nano-editor.org/dist/latest/cheatsheet.html

Exercise

Create a text file in your personal directory and fill it with some text.


GUI Based

When working with X forwarding, simple text editors with GUI features can be used. On the SPRAWL server, this includes mouspad or the minimal Python IDE idle.


Starting Applications

System wide binaries must be located in a directory that is listed in $PATH (see the final section on this page for details). They can be started by simply typing the name:

$ foo

A local binary named foo can be started with the following command:

$ ./foo

You can terminate your command with an ampersand (&) to run a process in the background. You can continue to work in the terminal, afterwards:

$ ./foo &
[1] 5459

If you start a command this way, it gives you an id of the background process in brackets and the actual process ID (PID).

You can get the process back into foreground with the fg command followed by the background process id:

$ fg 1

Check for Running Applications

At some point, users may want to know whether a process is running or which processes have been started. The command top lets you monitor the system processes with additional information on CPU and memory usage, updated with a fixed interval:

$ top

htop is a slightly polished version, using colored results:

$ htop

You can get a list of all running processes, including auxiliary ones, by typing:

$ ps aux

Usually, these are way to many results. If you want to check whether an instance of a specific program is running, you can use grep after the ps aux to filter the results:

$ ps aux | grep foo

Shell Variables

Sometimes it is convenient to store information in variables for later use. Some common variables that are used in Unix like operating systems like Linux, BSD or MacOS are for example PATH and DISPLAY.

Shell variables are usually uppercase. To get the content of a variable it is prefixed by a dollar sign. The command echo is used to print the content:

$ echo $PATH
/home/username/.local/bin:/home/username/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin
$ echo $DISPLAY
:0

Defining a variable is done with an equal sign. It happens quite often that the program that should use the variable, opens another environment. To access the variable in that sub-environment, it has to be exported before:

$ NAME=username
$ echo $NAME
username
$ bash
$ echo $NAME

$ exit
exit
$ export NAME
$ bash
$ echo $NAME
username


Contents © Henrik von Coler 2021 - Contact