compsci-missing_semester_2020/_subsections/lesson-05.org

#+title: Lesson 05 | Command line Environment
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* Links
#+attr_html: :class links
- [[../toc.org][TOC | Missing Semester]]
- [[https://www.youtube.com/playlist?list=PLyzOVJj3bHQuloKGG59rS43e29ro7I57J][Playlist: Missing Semester]]
- [[https://www.youtube.com/redirect?event=video_description&redir_token=QUFFLUhqbVVJc2RzZ25nMmlrVW5zVGRsTS1fX2ladmRPQXxBQ3Jtc0ttWjQ5Ujcyd19TekNncTZGNEp1eDc3RWhzTzhvMW9oSTFoUl9JbGt1Mi0yU3FLc00wVUx1UXNJdFQxTjBjMWphdUZxNnU1WUYzTmFqd3RRemNLUDBJMlZkV3B0SnB4RVhpaUhvWWtnc1RISW1WVzdYWQ&q=https%3A%2F%2Fmissing.csail.mit.edu%2F2020%2Fcommand-line%2F&v=e8BO_dYxk5c][class notes]]

- Curr: https://youtu.be/e8BO_dYxk5c?si=ttNryjIiOS0BxBqD&t=2542

*** timestamps
:PROPERTIES:
:CUSTOM_ID: timestamp
:END:

#+attr_html: :class playlist
+ [[https://youtu.be/e8BO_dYxk5c?si=A-imhHunQCtp_-Oz][00:00 - introduction]]
+ [[https://www.youtube.com/watch?v=e8BO_dYxk5c&t=138s][02:18 - Job Control]]
+ [[https://www.youtube.com/watch?v=e8BO_dYxk5c&t=227s][03:47 - Signal Interrupts]]
+ [[https://www.youtube.com/watch?v=e8BO_dYxk5c&t=360s][06:00 - Python Program]]
+ [[https://www.youtube.com/watch?v=e8BO_dYxk5c&t=672s][11:12 - The Kill Command]]
+ [[https://www.youtube.com/watch?v=e8BO_dYxk5c&t=881s][14:41 - Terminal Multiplexer]]
+ [[https://www.youtube.com/watch?v=e8BO_dYxk5c&t=1112s][18:32 - The Key Bindings]]
+ [[https://www.youtube.com/watch?v=e8BO_dYxk5c&t=1536s][25:00 - Dot Files]]
+ [[https://www.youtube.com/watch?v=e8BO_dYxk5c&t=1799s][29:59 - Context Based Configuration File]]
+ [[https://www.youtube.com/watch?v=e8BO_dYxk5c&t=2004s][33:24 - Terminal Emulator]]
+ [[https://www.youtube.com/watch?v=e8BO_dYxk5c&t=2196s][36:36 - Aliases]]
+ [[https://www.youtube.com/watch?v=e8BO_dYxk5c&t=2286s][38:06 - Common Folder Structure]]
+ [[https://www.youtube.com/watch?v=e8BO_dYxk5c&t=2344s][39:04 - Symlinks]]
+ [[https://www.youtube.com/watch?v=e8BO_dYxk5c&t=2552s][42:32 - ssh]] *current*
+ [[https://www.youtube.com/watch?v=e8BO_dYxk5c&t=2715s][45:15 - ssh keys]]
+ [[https://www.youtube.com/watch?v=e8BO_dYxk5c&t=3057s][50:57 - ssh config]]
+ [[https://www.youtube.com/watch?v=e8BO_dYxk5c&t=3231s][53:51 - changing the prefix]]

* notes

** topics
- job control
- terminal multiplexers
- dot files / how to configure
- work with remote machines

** job control
*** sleep
- puts process to sleep for a specified amount of time
- exit by typing Ctrl-C

*** Ctrl-C
- sends SIGINT - signal interrupt
- man signal will show the list of signals

** signals
- SIGQUIT :: signal sent when we want to quit
- SIGTERM :: similar to quit but not in term
- SIGHUP :: when we have processes running but still want to close

*** pausing
- SIGSTOP :: pause execution of program
- SIGCONT :: continue program

*** python library
- use import signal

#+BEGIN_SRC python
import signal
def handler(signum, frame):
    printf("signal received")

signal.signal(signal.SIGINT, handler)
#+END_SRC

- the above would catch a Ctrl-C and run it through handler
- you use this by catching a Ctrl-C and running any saves or cleanup before exiting

** nohup and jobs
- allows for a process to continue livign when the terminal is killed

*** example
- sleep put the process to sleep
- '&' puts the process in the background
  - wont take over the process

#+BEGIN_SRC bash
nohup sleep 2000 & python somprog.py
#+END_SRC

*** jobs
- ~jobs~
will show the suspended and running processes in background

- how to restart a suspended process
  - type 'jobs' to see what there is in this terminal
  - the find the jobs number, ie [1] or [2]
  - use the 'bg' command
    #+BEGIN_SRC bash
    bg %1
    #+END_src


** kill command
- allows you to send any kind of signal to a job

- e.g. "stop" will suspend but not close the job

*** some commands
- HUP :: Hang Up
- STOP :: suspend
- KILL :: kill it no matter what


** Terminal Multiplexer
*** overview
- tmux
- lets you create workspaces that you can work in
- rearrange the environment
- have different settings

*** core concepts
- hierarchy
  - sessions
  - windows
  - panes


** dot files
*** alias
- remap a source series of characters to a longer series
- alias takes a single argument, ie, do not use spaces
- to show what an alias refers to pass the alias to the alias command
  - e.g.
#+begin_src bash
~/somedirectory >>> alias myaliasedcommand
myaliasedcommand='ls -lah'
#+end_src

**** examples
- make an alias "ll" for a list command with flags
#+begin_src bash
alias ll="ls -lah"
#+end_src

- make an alias for git status
#+begin_src bash
alias gs="git status"
#+end_src

- alias to prompt for an override
#+begin_src bash
alias mv="mv -i"
#+end_src

*** text based configuration 'dot files'
- called 'dot files' because they start with a dot
  - .bashrc
    - must be in the home directory
  - PS1
    - prompt variable for your prompt
    - you can set it in the .bashrc file
    - ~PS1=" >> "~

  - .vimrc
    - vim configuration file

** tmux
- run a session, detach and get back to it later

*** link
- [[https://tmuxcheatsheet.com][cheat sheet]]
- [[https://www.youtube.com/watch?v=nTqu6w2wc68][network chuck tutorial]]

*** prefix key
Ctl-B

*** userful commands
**** detach / attach
- Ctl-B , D -> detach
-  tmux a -> reattach

**** reattach to most recent session
- tmux a

**** attach to a particular session
- list the tmux session
- note the index number or name
- attach to that index -t (target)
  ~tmux a -t [INDEX]

**** kill
***** kill a session
tmux kill-session -t [INDEX]

***** kill session from list windows
- go into list windows C-b w
- highlight the one you want dead
- C-b x, it will ask for confirmation

***** kill ALL sessions
tmux kill-server

***** kill a pane
C-b x

***** kill an entire window
C-b &

**** tmux names session
-
  ~tmux new -s name~

****  list session
- tmux ls

*** 3 layers
**** layer 1 -> sessions
- when you hit tmux you start a new tmux session

**** layer 2 -> window
- when you create a new session, you automatically create an initial window

- C-b c :: create a new window in addition to the existing ones
  - all windows will be listed in the display line at the bottom
  - the * indicates the current

- C-b n :: move through your windows
- C-b < :: rename window
- C-b w :: list all sessions and windows
  - you can walk through the list using arrow keys
  - enter to switch

***** kill session
- go into list windows C-b w
- highlight the one you want dead
- C-b x, it will ask for confirmation

**** layer 3 -> panes
- panes exist in windows
- add horizontal pane :: C-b %
- add vertical pane :: C-b "
- switch panes :: C-b [arrow]
- show pane index :: C-b q
- switch to pane index :: C-b q [index]
- change pane size :: C-b [hold Ctl] [arrow]

***** preselected pay layout
- C-b Alt-1-5

***

**  terminal emulator - alacritty
- very fast
- useful for heavy displays like neoviim
- vm mode is good for reloading

*** hint system
- pattern recognition of terminal output based on regex
- execute commands on those patterns

**** e.g.
- url will be opened in browser

**** custom actions
- shows hints overlay over something recongized
- for files or other customized action

*** themes
- black theme

*** copy mode / vim
- treat terminal output as a vim buffer
- doesn't support all, but a lot

** aliases
you can find good alias lists online

** common folder structures
- use symlinks to store all your dotfiles in one directory

- ~ln -s [path-to-orig] [path-to-link-location]~

#+begin_src text
~
├─ .bashrc
├─ .vimrc
└─ dotfiles
   ├─ bashrc
   └─ vimrc
#+end_src

** ssh
- working with remote machines
- it is good for opening connections
- can execute commands remotely, and piping back the output to the calling shell
  ~ssh username@some-ip.com ls -la~

** ssh keys
- typing passwords is inconvenient
- use public key encryption
  - public, private
  - give public key to the server
  - whenever you try to authenticate use your private key

*** create a key
~ssh-keygen -o -a -t ed25519~

- passphrase gives extra protection bc a user of the private key has to give a password

- creates
  - private key: id_ed25518
  - public key: id_ed25519.pub

*** move the public key to the server
#+begin_src bash
cat ~/.ssh/id_ed25519.pub | ssh username@ip-address.com tee .ssh/authorized_keys
#+end_src

- at that point ssh will ask you for the password for the server and then it will put the key where you sent it
- 'tee' sends standard input both to the screen and to a file (so you can see what is being saved)

**** ssh-copy-id
- does the above but in one command
~ssh-copy-id username@ip-address~


** copy files remotely
*** scp
~scp filename.ext username@ip-address:/path/to/new-filename.ext~

*** rsync
- copy a LOT of files remotely
- rsync can continue from interrupts


~rsync -avP /folder/to/copy/from username@ip-address:/folder/to/copy/to~

** ssh config

Host hostname
  User username
  HostName ip-address
  IdentityFile ~/.ssh/id_ed25519
  RemoteForward 9999 localhost:8888