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Gabriel Arazas ed7181bd03 Update my notebook as of 2021-06-05
2021-06-05 08:32:50 +08:00

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Anki: 2021

My collection of tips and tricks I collected in 2021.

Finding devices

Front

How to list devices information? (I mean all sorts of devices.)

Back

  • lspci lists PCI devices.
  • lsusb list USB-connected devices.
  • lsblk list the block devices which usually includes storage drives and such.

$PATH environment

Front

How does a shell find the binaries?

Back

Most shell searches through the $PATH variable, a colon-delimited list of paths containing the binaries.

Testing systemd timestamps

Front

How to test out systemd timestamps?

Back

systemd-analyze {calendar,timestamp,timespan}

To know how the format (i.e., calendar, timestamp, and timespan) looks like, you can refer to man systemd.time.5.

Enabling desktop integration

Front

How to make desktop environments recognize the desktop files?

Back

Most of the desktop environments and certain applications like Rofi refers to the XDG_DATA_DIRS environment variable, a list of colon-delimited paths similar to PATH.

This enables desktop integration with certain tools like Nix and Guix package manager. Here's how to integrate installed Nix packages into the desktop.

XDG_DATA_DIRS=$HOME/.nix-profile/share:${XDG_DATA_DIRS:-/usr/local/share:/usr/share}

Flatpak permissions

Front

What permissions does user-installed Flatpak apps have by default?

Back

By default, they have none. Among the default limitations:

  • They can only access their own runtime folder $HOME/.var/app/${FLATPAK_APP_ID}.
  • They cannot access the network.

Some apps are installed with the request to allow the following permissions enabled (e.g., Zotero).

If left with no permissions, you'll see in certain situations like a file browser dialog that the permissions is in effect. Below are some of the examples interacting with the permissions of an app.

# Show the permissions of an app.
flatpak permission-show ${FLATPAK_APP_ID}

# Let the user-installed Flatpak app access the home directory.
flatpak override --user --filesystem=home ${FLATPAK_APP_ID}

The basics of Flatpak apps

Front

What is a Flatpak package? Does it have its own form of managing dependencies?

Back

A Flatpak package can either be a runtime or a standalone app.

Runtimes are the basic dependencies of an application. Only select packages available as a runtime (e.g., Qt, GTK).

Flatpak has its set of runtimes composed of system libraries to be used with the applications. Thus, it stays out of its way with the operating system's libraries. The developer can also bundle its own set of libraries.

Changing user shell

Front

How to change user shell in most Linux distros?

Back

chsh

Printing a list in the shell

Front

Give some ways to print a list.

Back 

# Format the string.
printf "%s\n" foo bar 'baz ;;'

# Echo the string as-is.
echo "foo
bar
baz ;;"

# Print with escaped newlines.
echo -e "foo\nbar\nbaz ;;"
foo
bar
baz ;;
foo
bar
baz ;;
foo
bar
baz ;;

systemd timestamp example

Front

What is *-*-8/4 in systemd calendar format?

Back

Every 4 days, starting from the 8th of the month.

Assuming this was executed on 2021-05-12.

systemd-analyze calendar *-*-8/4
  Original form: *-*-8/4
Normalized form: *-*-08/4 00:00:00
    Next elapse: Sun 2021-05-16 00:00:00 PST
       (in UTC): Sat 2021-05-15 16:00:00 UTC
       From now: 3 days left

Type checking in Bash

Front

Implement a little bit of type checking in Bash.

Back

printf throws an error if the given argument is not appropriate.

# This is fine
printf "%d\n" 532 429 40 102

# This will return a non-zero exit code
printf "%d\n" this_will_throw_an_error 430 that_previous_number_will_not

# This is also fine
printf "%f\n" 10 43.45 3.14
532
429
40
102
0
430
0
10.000000
43.450000
3.140000

Emacs: The overview of buffers

Front

What is an Emacs buffer?

Back

A buffer is anything that Emacs displays. It usually display file contents among other examples with butterfly, doctor, or the starting buffer when you first open Emacs.

While buffers usually have an associated file path, a buffer doesn't need one. This is one of the concepts that is applied to other text editors (Vim, Atom, Visual Studio Code).

The basics of Emacs modes

Front

What is a mode in Emacs?

Back

A mode is set of behavior quite similar to Vim modes.

Emacs further divides modes into two.

Major modes are Emacs' way of supporting programming languages and file formats. Programming language support usually comes in major mode — e.g., R-mode for R files, python-mode for Python scripts, org-mode for Org mode documents. Think of them as an equivalent to Vim's filetype. Only one major mode can be activated in one buffer at a time and all buffers have a major mode.

Minor modes usually contain little behavioral changes that improve the editing experience. When enabled, some of them are global modes — affecting every buffer in your session. Others are only buffer-local — affecting only the buffer when you activated the mode. Unlike major modes, multiple minor modes can be enabled at any given time.

Emacs: Eagle's eye view of a window

Front

What is considered window in Emacs?

Back

A window is where the buffers are being displayed. One window can display all buffers but only one at a time. To display two buffers at a single time, just add another window.

All windows display the same buffer; if the buffer is modified in one of the window, it will show the changes in all windows.

Emacs: Point and marker

Front

What is a point and a marker in Emacs?

Back

A point is the current location of the cursor in the buffer. You can get the point with point function. Often helpful for interacting with buffers.

A marker is another point in the buffer. It is usually found when interacting with regions when asked for the two points (i.e., the beginning and the ending position). Furthermore, a marker can be used to save locations and jump back to that marker when asked.

Interacting with buffers in Elisp

Front

Give a rough example on how to do the following in Emacs Lisp:

Create a temporary buffer named "hello" containing an Org mode document with a "Hello world" entry.

Back 

(with-temp-buffer
  (insert "* Hello world")
  (rename-buffer "hello")
  (org-mode))

String comparison in Emacs Lisp

Front

How to compare two strings in Emacs Lisp?

Back

(string= STR1 STR2)

(print (string= "WHOA" "whoa"))
(print (string= "WHOA" (upcase "whoa")))
(print (string= "Hello world" "HeLL0 World"))

nil

t

nil

Using the help system in Emacs

Front

Name different ways to use the help system inside Emacs.

Back

  • help-for-help is the most comprehensive help section (in my opinion).
  • describe-* series of functions are the next. Among the list of describe functions, you have: describe-key, describe-function, describe-variable, and describe-package. You can just open up the minibuffer and see what else is there.
  • apropos is similar to Unix apropos command which searches for every symbol in Emacs.

Emacs: Word manipulation

Front

Give some functions on word manipulations inside Emacs.

Back

The following functions have multiple variations each for a character ($F-char), word ($F-word), region ($F-region), and region or point ($F-dwim).

  • capitalize-* for making the first of the word in uppercase.
  • downcase-* for making a region all lowercase.
  • upcase-* for making a region all uppercase.

evil-mode has a keybinding associated with uppercase and downcase a certain region with evil-upcase and evil-downcase, respectively.

Emacs: Line manipulation

Front

Give some functions on manipulating lines while in Emacs.

Back

  • evil-mode has evil-join which works the same way Vim's join complete with smart spacing and everything.
  • fill-region is useful for formatting requirements/preferences like in the Linux kernel where the maximum width of 80 characters. evil-mode has an associated keybinding function with evil-fill.
  • sort-lines is pretty useful for the common task of sorting lines. Though, not useful for items that consist of multiple lines.

Vim: Jump to previous jump point

Front

In Vim, how to get back in previous jump point?

Back

Ctrl + O

Remember it as getting out of the current jump point and back to the previous one.

Vim: Enter jump point

Front

How to jump into a keyword with Vim?

Back

  • Ctrl + ] will enter into the definition block of a keyword.
  • K also has the same effect.

Vim: Go to file path

Front

In Vim, how to go to the file path at point?

Back

gf (in normal mode) as in goto file.

Set as a pager

Front

How to set Vim as a manpager?

Back

MANPAGER="nvim +Man!"

+Man! is a command invocation (as if entering :Man inside Vim). It can also be written as -c Man!.

The :Man! command displays the current buffer as a manual page.

Vim: Show outline/table of content

Front

How to show the table of contents of a document in Vim?

Back

gO, although the results are filetype-specific (and some don't have any). Helpful examples include for manual pages and help pages (from :help).

Detect files through Vim filetypes

Front

How does Vim detect the files?

Back

Vim guesses the file by assigning filetypes, mainly through the file name and reading the file content. A filetype is how Vim knows what plugins to apply to the current buffer.

Vim has a few built-in filetypes such as shell, manual pages, Markdown, Asciidoc, xmodmap, patch files, and JSON among others (that are in $VIMRUNTIME/filetype.vim).

For more information, run :help filetype inside Vim.

Going to keyword definitions in Vim

Front

How to go to the keyword definition in Vim?

Back

gd as in go to definition.

Though, not all the time it will do what its supposed to do. For better effect, you can generate a Ctags file which Vim has a built-in integration (see :h ctags).

Vim modes

Front

What is a mode (in Vim)?

Back

A Vim mode is a set of behavior and actions. In this case, it considers editing and navigation (among other modes) to be separate. Thus, you need to switch between them to do those things.

Vim has built-in modes which you can see with :h vim-modes.

Word wrapping in Vim

Front

How to do word wrapping (in Vim)?

Back

gw as in go format the words. By default, it simply line wraps the lines with the 80-character limitation.

Using the help system

Front

How to effectively make use of the help system of Vim?

Back

The usual way is to execute :h or :help. You can view what does a keybinding do with :h ${KEYBINDING} — e.g., :h gw to know what gw does, :h V for viewing visual line mode. For keybindings in visual and command line mode, prepend them with v_ and c_, respectively.

Pitfalls and illusions of competence

Front

Give various pitfalls and illusions of competence to look out when learning.

Back

  • The presence of the material itself can cause students to foolishly think they already know about the subject.
  • Similarly, studying with solutions can be a trap if you focus on the what and how rather than the why.
  • Various common practices such as highlighting, rereading, and mind mapping are not as effective and only applicable in specific situations.
  • The einstellung mindset, being invested in an idea that you can't see other solutions.
  • Similarly, overlearning can occur if you're aiming for complete mastery when you should move on after understanding the concept.

org-babel

Front

What makes Org mode popular for reproducible research?

Back

org-babel, the library that enables superpowers for Org mode source code blocks.

Among the list of features, org-babel makes the following things easier for creating lab notebooks.

  • Execute the source code block and print results.
  • Create files from source code blocks, making it possible to create an entire computational report with a single Org mode document.
  • Metaprogramming with noweb-inspired system making dynamic content possible.
  • Individual control over source code blocks with sessions, export options, and variables.
  • Pass values between different source code blocks even in different programming languages.

org-babel modes

Front

How to make org-babel pass values between different source code blocks?

Back

First, configure org-babel to work in functional mode (i.e., :results value) in a source code block. With functional mode, it will return values which will be handled by org-babel.

#+name: num
#+begin_src python  :results value
return 53
#+end_src

The value cannot be passed unless it has a name that others can reference yet so add a name property to the source code block (i.e., #+name: ${NAME}).

Now here's a different source code block written in a different language. To pass a value, you have to configure with :var ${VARNAME}=${NAME}.

#+begin_src ruby  :var num=num  :results output
print(num)
#+end_src

Creating files with Org mode

Front

How to create files with Org mode source code blocks?

Back

The :tangle option enables extracting code blocks into files. Accepted values include yes, no, or a relative path to the Org document where the file will be written.

Dynamic content with Org mode

Front

Is creating dynamic content in Org mode possible? If so, how?

Back

Yes!

By attaching a name to a code block and evaluating them, it is possible.

Here's an example of a source code block with a default argument.

#+name: greeting
#+header:  :var name="World"
#+begin_src sh
echo "Hello ${name}"
#+end_src

You can then call the function in different ways:

  • For calling it inline, call_${FUNC_NAME}().
  • For creating a block, #+call: ${FUNC_NAME}().
  • For invoking inside a code block, <<${FUNC_NAME}()>>, but you have to enable noweb (e.g., :noweb yes).

You can then pass header arguments by appending in square brackets ([]) before invoking it — e.g., call_greeting[:results replaces](), #+call: greeting[:results replace](), <<greeting[:results replace]()>>.

Org mode: Asciidoctor-styled callouts

Front

Are Asciidoctor-style callouts possible in Org mode? If so, how?

Back

Surprisingly, yes! It is just hidden on the documentation. Specifically, on the Literal examples section of the Org mode manual.

Here's an example to do it.

#+begin_src python
print("Hello world") # (ref:hello)
print(2 + 5)         # (ref:num)
#+end_src

In [[(hello)][line 1]], we have printed the traditional "Hello world" program.
In [[(num)][the second line]], we've done a simple arithmetic and printed it into the console.

To create Asciidoctor-styled callouts, create a reference inside of the code block and refer to it (i.e., (${ref})).

Org mode: Timestamps and durations

Front

How to denote timestamps and durations in Org mode?

Back 

# A timestamp looks like this.
<2021-05-07 Fri>

# To make a duration, just put two dashes between two timestamps.
<2021-05-07 Fri>--<2021-05-08 Sat>

To make creating timestamps easier, execute org-time-stamp (or whatever keybinding you've set).

Org mode: Deadlines and schedules

Front

How to make deadlines and schedules in Org mode entries?

Back

Just prepend the keywords DEADLINE and SCHEDULED, respectively.

DEADLINE: <2021-06-30 Wed>
SCHEDULED: <2021-06-29 Tue>

Org mode: Quick file navigation

Front

Give some ways how to navigate Org mode documents quickly.

Back

  • I don't need to explain what org-babel-next-src-block and org-babel-previous-src-block does.
  • org-backward-heading-same-level is the same as org-forward-heading-same-level but moves one headline backwards.
  • org-forward-heading-same-level moves one headline forward in the same level. Useful for navigating sections and subsections.
  • org-goto creates an interface for showing the outline and it is a great navigation function. Highly recommend to use it with a completion interface (e.g., counsel-org-goto, counsel-org-imenu).
  • org-num-mode adds a (non-persistent) counter to the document. Very helpful in navigating larger files.
  • org-sort will sort the entries into your preferred criteria. It also works on a list of items which is very useful if one of the list items has more than one line.

Editing source code blocks in Org mode documents

Front

What function creates a buffer for certain elements in org-mode but it is especially useful for editing source code blocks where it will open with the correct major mode?

Back

org-edit-special

Practices for studying

Front

Give various practices for studying effectively.

Back

  • Recalling is one of the more effective practices compared to rereading or highlighting. Self-testing is one of the better strategies, overall.
  • Prefer spaced repetition over cramming as scientifically, the learning process takes some time to settle.
  • Get the key ideas ahead and as you're studying, fill the details. This includes skimming — reading through the chapter, looking at the keywords.
  • Practice interleaving your studies — that is, studying other subjects and/or moving to later topics as you understand the topic.
  • Focus, understand, and practice. Learning can occur bottom-up (learning the details of a problem) and top-down (learning the bigger picture of a topic). Using both creates context and that's where you put your understanding to the test as you learn when to apply what you've learn.
  • Use memory palace technique — that is, to create analogies, narratives, and mnemonics.
  • Have efficient amount of sleep. Sleep has certain processes that helps our brain like removing toxins in our brain that accumulate when we're awake, eliminating less relevant neural structures in favor of strengthening stronger ones for tomorrow, and thinking of a solution of the thing you worry about.

Focused and diffused mode

Front

What is focused and diffused mode? When those two modes often found in certain situations?

Back

Focused mode is when you are in the middle of a mentally intensive task — e.g., cooking, writing, reading, studying. In this process, you gather all of the information that are immediately required to complete it.

Diffused mode is the state of mental relaxation — e.g., taking a walk, watching a movie, recess and lunchtime. This is when the brain takes the focused task into the background and let random thoughts pass by. This is the reason why we sometimes get a sudden realization (a Eureka! moment).

Benefits of sleep

Front

How does sleep help in the learning process?

Back

Sleep has certain processes that helps our brain.

  • Removing toxins in our brain that accumulate when we're awake.
  • Eliminating less relevant neural structures in favor of strengthening stronger ones for tomorrow.
  • Thinking of a solution in the background of the thing you worry about.

Bash conditional with an unset variable

Front

In Bash, what does ${HOME:-"/home/me"} means?

Back

If $HOME is unset, substitute with the given value (i.e., /home/me).

Bash conditional with a set variable

Front

In Bash, what does ${HOME:+"/home/me"} means?

Back

If $HOME has a value, then return the given value (i.e., /home/me).

Shell help system

Front

Give some ways to make use of the help system in the shell (or most Unix environment).

Back

  • help sections (i.e., --help or -h)
  • manual pages (i.e., man)
  • TexInfo (i.e., info)
  • tldr pages (i.e., with clients like tealdeer)

Basic music notation reading 1

Front

What notes are displayed (in order)?

<<lilypond-paper-config>>
{
  c a' f b
}

/foodogsquared/wiki/media/commit/3be6f5256b463a44289adcbe06a24e9d2cff0aca/cards/assets/2021/basic-notation-reading-1.png

Back

C A F B

Basic music notation reading 2

Front

What notes are displayed (in order)?

<<lilypond-paper-config>>
{
  \chordmode { c1 }
  \relative c' { e f a }
}

/foodogsquared/wiki/media/commit/3be6f5256b463a44289adcbe06a24e9d2cff0aca/cards/assets/2021/basic-notation-reading-2.png

Back A

C major triad (i.e., C E G). Then the notes E, F, and A.

Basic music notation reading 3

Front

What notes are displayed (in order)?

<<lilypond-paper-config>>
{
  c''1 d' <c' a'> <e' b'> <f'' g'>
}

/foodogsquared/wiki/media/commit/3be6f5256b463a44289adcbe06a24e9d2cff0aca/cards/assets/2021/basic-notation-reading-3.png

Back

C, D, C-A (a major sixth), E-B (a minor fifth), and G-F (a seventh).

Watch the logs of a systemd unit

Front

What is happening with the following command?

journalctl -u backup -fb

Back

Watch the logs from the systemd unit backup.service starting from boot time.

The command could also be written in the same way.

journalctl --unit backup --follow --boot

Restoring a file in Git

Front

How to restore a file in Git?

Back 

git restore $FILE_PATH

Despite the name, it will also delete the file if it's detected as untracked file in the Git worktree.

Setting environment variables with systemd environment directive

Front

How to set environment variables with systemd?

Back

Create an environment directive file in the specified directory. You can find the search paths and the syntax from environment.d.5 manual page.

Basically, it is a shell-like config for setting environment variables. The following shows that.

TERM=alacritty
EDITOR=nvim
BROWSER=brave
MANPAGER="nvim +Man!"

PATH=${PATH:+$PATH:}${GUIX_PROFILE:-$HOME/.guix-profile}/bin
XDG_DATA_DIRS=${GUIX_PROFILE:-$HOME/.guix-profile}/share:${XDG_DATA_DIRS:-/usr/local/share:/usr/share}

Compared to exporting values with the user shell (e.g., .bashrc, .zshrc) where they are only applied when the shell is called, environment variables generated from the directive can be recognized from applications that called non-interactively (e.g., GNOME desktop search, Rofi).

You can also view the resulting environment with systemctl show-environment.

Emacs Lisp conditionals

Front

Give some functions for creating a conditional in Emacs Lisp.

Back

Below are the common way to control the flow with Elisp.

(if (and nil nil)
    "Hello there!"
  "Not hello there, sith lord!")

(unless t
  "Not hello there, sith lord!")

(when t
  "Hello there!")

Finding out file types in the shell

Front

Give some ways how to show the file type in the shell.

Back 

file --mime-type $FILE
xdg-mime query filetype $FILE

I prefer file --mime-type since it is clearer on purpose and name alone.