LIS-3353 - Command Line

Also — "THE CLOUD"


There is no cloud, it's just somebody elses computer


A computer (possibly virtual), probably running Linux

Yep. Usually.


Funny, it's not talked about that much. Or enough.
Again, not the part that makes people Rich, or even popular


Why do we even use "cloud?"


After all, email is "cloud" and yet we never used that word.


Probably a B2B thing — this was the first time the SERVERS were freed from the bare metal



On Virtual

Many different ways to do "Virtual" and "Virtual-like," but roughly:


VIRTUALIZATION and CONTAINERIZATION


Pure Virtual


i.e. literally fake the whole computer. You have to install the OS, etc.



Containers

This is "Docker" et al:


You don't fake the whole computer;
you wrap up and "package" the stuff you need to use;
and try to wall it off from everything else.


When you get big, you have to think about this large scale

e.g. KVM
Kubernetes
and other tools for managing A BUNCH OF THESE.


Also, there's the Proton/Wine thing



But may be big in the future in terms of Linux killing windows;
given that games are usually the hardest thing to emulate.


more on containers later...


Shell Scripting - Command line

That default thing that comes up on all the unixy-linuxy systems everywhere.


It’s a text interface. You type commands into it and the computer responds.
And it’s also a "programming" language. As in, you can type in more than one command in a row, save it to a file, and run the file. So, you know, "programming."


Names of things


Fundamental ideas:

(ignore basic programming ideas like "objects" for now)




Again

SCRIPTING is as much about
Using programs that ALREADY EXIST TOGETHER
as it is
Making new programs.


("Libraries" on steroids?)


Users and Permissions..

..actually mean something today


ROOT – Like “Administrator” or maybe “God”
users – humans
(..and others – fake “users” to get tasks done)


Some systems (eg Ubuntu) allow for Super Users
S.U.- do “this” = sudo



Permissions

Three major things you can do with files


Three important “groups”


Permissions for Directories

..are weird


(create new/delete existing files, or rename them)


Practical Permission Problems


A Basic Linuxy Filesystem



Commands in theory

Any IMPERATIVE action the computer can do. Can be one word or more.


Ultimately, will be an ORDER, usually expressible as a VERB


Are VERY closely related to (if not identical) to FUNCTIONS/METHODS


"Computer! Do THIS!"


ls


Commands in theory

Since we're in the command line we are always acting on:


FILES and/or TEXT. These will be input and/or output.


if commands are VERBS, the FILES and TEXT are the nouns/objects
We call these expressions


(and of course, the TEXT can lead you to something else, like a FOLDER) 


cat file.txt
echo "Hi there"
ls "/home/mine"


Nearly every command can act on either TEXT or FILES or BOTH.


Commands in Theory

We've talked VERBS and NOUNS. But we might want to modify the operation of things;
Think ADVERBS and/or ADJECTIVES:


On the command line, these are called options

one dash + letter (ls -a)
two dashes + words (sort --reverse)


Getting Help



but seriously, Google/Duckduckgo etc


More

Check out your distro's "Software Center"
and/or
"Package Manager"


File Manipulation




Viewing Text and Files

cat - "Good" example of "efficiency" at the expense of "redundancy"
i.e. it means "concatenate" — which is to squish two files together and print to the screen. But it can also do it with just one file.


less - this is such a terribly bad joke I hate even explaning it


Let's slow down here,

because here is the power:


One way to describe cat - It "shows you the file"


BUT, let's be VERY precise here:
Cat TAKES A LINE OF TEXT (that refers to a file)..
and PRINTS IT ON THE SCREEN


TAKES A LINE OF TEXT = "Standard Input or stdin"


PRINTS IT ON THE SCREEN "Standard Output or stdout"


Pipes and Redirects

Default is to read from stdin, and write to stdout.
But by changing the default NOW YOU'RE PLAYING WITH POWER



(interesting then , cat goes from FILE to TEXT, and > goes from TEXT to FILE )


BIG OVERARCHING POINT..

THAT'S MY OPINION


If it works and its clearer to you, don't let the supernerds tell you it's a bad idea e.g.
"Useless use of cat" IS FINE


BASH

BASH (Bourne Again) Shell - others are fish and zsh, etc


Lots of “tricks” are available here, eg


and many MANY more...


BASH

Furthermore, you can modify this environment to fit your needs, via:
.bashrc
(stuff here will be run everytime you open a terminal)


A great example is the “alias” command. If a command doesn't exist for what you want to do, just ,ake up your own!


alias modbash='nano ~/.bashrc'


Newer Shells

You may see some like
"zsh" or "Zshell"
or Fish
or Oilshell


Roughly, they're a bit nicer to use, but are not "backwards compatible"
which may not matter. Feel free to try them out!


(later on, be careful when NOT using them interactively/as a REPL)



Viewing Files

IN TERMINAL


ALSO


Opening Files


COMMAND/ARGUMENT STYLE



Keeping it simple at first:


SORT

sorting text



GREP

searching text for matches


grep OPTIONS PATTERN (FILE)
Can search over FILES or STDIN
Also, can search ONE FILE or MANY (check -d or -R)
useful flags:
-i (case insensitive)
-v (invert search/show NON-matches)
-l (just show matching FILES, not lines)


(see also "ripgrep" or rg)


Classic Bash Commands

- sed
- awk
- find
- locate


Some nicer ones

head
and
tail


for getting only part of a file, by lines



tr


"Transliterate"


Easier way to do SINGLE CHARACTER deletions or transforms
(but can act on "groups," like "A-Z"


cut


Nice way to cut up lines. Just specify the "delimiter"
(the character you'll divide on)
and "which field" by number


echo "first:second:third" | cut -d ':' -f2
yields second


CLI vs GUI


Command Line Interface


vs.


Graphical User Interface
(but, why not both)


CLI, but GUIish

(hardcore nerds may distinguish and call these TUIs)



"ncurses"


From CLI to GUI


firefox http://jrm4.com
or
firefox /home/myuser/html/testindex.html


(NOTE, closing the terminal may also close the program)