Notes for 2024-02-01 (#1)

Database system concepts and Nix's `callPackage`.

Reviewed-on: #1
Co-authored-by: Joshua Potter <jrpotter2112@gmail.com>
Co-committed-by: Joshua Potter <jrpotter2112@gmail.com>

notes/.obsidian/plugins/obsidian-to-anki-plugin/data.json

@@ -60,14 +60,19 @@
     "Linux/Signals.md": "f58f1a36a9fe53928fdc3dc02fc4c3e3",
     "linux/index.md": "6e50c924ee9e09294fd3b907fbdeaf0f",
     "linux/signals.md": "e9ab74723981ebc232189c84d3b0da74",
-    "templates/daily.md": "0f22c7ef0b0f35efada88d61c95e9815",
+    "templates/daily.md": "7866014e730e85683155207a02e367d8",
     "daily/2024-01-31.md": "72e343cef8d56e169cac7b360a88fcf0",
     "posix/index.md": "f7b1ae55f8f5e8f50f89738b1aca9111",
-    "posix/signals.md": "26161c6a79a0c413032c6c17e460412c",
+    "posix/signals.md": "2120ddd933fc0d57abb93c33f639afd8",
-    "gawk.md": "9bf70ef138a9a281b86400aee393cae7",
+    "gawk.md": "4517acfbf4e186e8cc66a9002fbad73f",
     "bash/index.md": "3b5296277f095acdf16655adcdf524af",
-    "bash/shebang.md": "bc30f75bcddff59d6f907fae89c17283",
+    "bash/shebang.md": "ad178efeb4a05190b80b5df108c175c7",
-    "bash/robustness.md": "e474fd33469fc393bfde45cd7b9411ba"
+    "bash/robustness.md": "de97cd77aae047b5eea27440b43c9c42",
+    "journal/2024-02-01.md": "f4cc061bfc8e41ce15ae9a354c65ffe9",
+    "journal/2024-01-31.md": "7c7fbfccabc316f9e676826bf8dfe970",
+    "bash/quoting.md": "b1d8869a91001f8b22f0cdc54d806f61",
+    "nix/callPackage.md": "5ef6bc5d1a549c55d43ebb4d48c64427",
+    "nix/index.md": "dd5ddd19e95d9bdbe020c68974d77a33"
   },
   "fields_dict": {
     "Basic": [

notes/bash/quoting.md

@@ -0,0 +1,47 @@
+---
+title: Quoting
+TARGET DECK: Obsidian::STEM
+FILE TAGS: bash
+tags:
+  - bash
+---
+
+%%ANKI
+Basic
+How do you escape a `'` within a single-quote string?
+Back: This is impossible.
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+<!--ID: 1706816752230-->
+END%%
+
+%%ANKI
+Basic
+What does the null string refer to?
+Back: The empty string, i.e. `""`.
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+<!--ID: 1706816752237-->
+END%%
+
+%%ANKI
+Basic
+When does Bash remove null strings from a command?
+Back: When they occur as part of a non-null command-line argument.
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+<!--ID: 1706816752241-->
+END%%
+
+%%ANKI
+Basic
+Why does the following not work correctly?
+```bash
+$ # -F specifies the field separator
+$ awk -F"" 'program' files
+```
+Back: Bash removes the null string before executing the command.
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+<!--ID: 1706816764555-->
+END%%
+
+## References
+
+* Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)

notes/bash/robustness.md

@@ -7,7 +7,9 @@ tags:
   - shell
 ---
 
-An interesting point Robbins[^robbins] discusses in his introduction to [[gawk]] is this idea of command robustness. He states that:
+## Overview
+
+An interesting point Robbins discusses in his introduction to [[gawk]] is this idea of command robustness. He states that:
 
 > A self-contained shell script is more reliable because there are no other files to misplace.
 
@@ -27,7 +29,7 @@ Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 202
 <!--ID: 1706726911475-->
 END%%
 
-The point he is arguing is that the first command below is considered more robust than the second since the command is more loosely coupled to its environment:
+He argues that the first command below is more robust than the second since the command is more loosely coupled to its environment:
 
 ```bash
 $ awk 'program' input-file1 input-file2 ...
@@ -55,4 +57,6 @@ It's interesting to think what else can be used as a measure of a command's robu
 * Whether a program acts atomically
 	* Is it possible intermediate files are left that affect subsequent runs?
 
-[^robbins]: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+## References
+
+* Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)

notes/bash/shebang.md

@@ -6,6 +6,8 @@ tags:
   - bash
 ---
 
+## Overview
+
 The shebang (also writting shabang or sha-bang) is a magic character at the start of a script indicating what command should be run when invoking the script directly. It always begins with ASCII characters `#!`.[^mendel]
 
 %%ANKI
@@ -44,12 +46,13 @@ Some systems limit the length of interpreters to just 32 characters. A simple wo
 
 %%ANKI
 Basic
-What workaround is used when shabang interpreter names are too long?
+What workaround is used when shebang interpreter names are too long?
 Back: Introduce a symbolic link.
 Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
 <!--ID: 1706726911470-->
 END%%
 
-[^mendel]: Cooper, Mendel. “Advanced Bash-Scripting Guide,” n.d., 916.
+## References
 
-[^robbins]: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+* Cooper, Mendel. “Advanced Bash-Scripting Guide,” n.d., 916.
+* Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)

notes/gawk.md

@@ -8,7 +8,7 @@ tags:
   - gawk
 ---
 
-## Introduction
+## Overview
 
 %%ANKI
 Basic
@@ -25,7 +25,7 @@ Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 202
 <!--ID: 1706726911439-->
 END%%
 
-> Dark corners are basically fractal - no matter how much you illuminate, there's always a smaller but darker one.
+> Dark corners are basically fractal - no matter how much you illuminate, there's always a smaller but darker one. #quote
 
 The above quote is attributed to Brian Kernighan (one of the authors of the [[C]] K&R book).
 
@@ -38,7 +38,7 @@ END%%
 
 ## Setup
 
-Robbins[^robbins] suggests executing command `set +H` on [[bash]] startup to disable [[C]] shell-style command history.
+Robbins suggests executing command `set +H` on [[bash]] startup to disable [[C]] shell-style command history.
 
 ## Usage
 
@@ -83,4 +83,111 @@ Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 202
 <!--ID: 1706726911454-->
 END%%
 
-[^robbins]: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+%%ANKI
+Basic
+Write the `awk` command that searches file `mail-list` for string `li`.
+Back:
+```bash
+$ awk '/li/ { print }' mail-list
+```
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+<!--ID: 1706819150999-->
+END%%
+
+%%ANKI
+Basic
+How is an `awk` rule without a pattern interpreted?
+Back: As applying the specified action for every input line.
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+<!--ID: 1706822165633-->
+END%%
+
+%%ANKI
+Basic
+How is an `awk` rule without an action interpreted?
+Back: As printing every line matching the specified pattern.
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+<!--ID: 1706822165637-->
+END%%
+
+%%ANKI
+Basic
+Describe what the following command does in in a single sentence:
+```bash
+$ awk 'length($0) > 80' data
+```
+Back: Prints every line of `data` that is longer than `80` characters.
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+<!--ID: 1706822165641-->
+END%%
+
+**Targets** are specified as `$n` where `n` is a placeholder for the `n`th whitespace-separated **field**s of the input line. For example, `$1` refers to the first field of the input line. `$0` is a special target referring to the entire list of arguments, i.e. the entire line.
+
+%%ANKI
+Basic
+What is `$0` a placeholder for?
+Back: The entire input line.
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+<!--ID: 1706823790230-->
+END%%
+
+%%ANKI
+Basic
+What is `$1` a placeholder for?
+Back: The first field of the input line.
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+<!--ID: 1706823790233-->
+END%%
+
+%%ANKI
+Basic
+What is the `BEGIN` pattern?
+Back: Code associated with it executes before any input is read.
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+<!--ID: 1706823790236-->
+END%%
+
+%%ANKI
+Basic
+What is the `END` pattern?
+Back: Code associated with it executes after all input has been read.
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+<!--ID: 1706823790239-->
+END%%
+
+%%ANKI
+Basic
+Describe what the following command does in in a single sentence:
+```bash
+$ awk 'NF > 0' data
+```
+Back: Prints every line of `data` with at least one field.
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+<!--ID: 1706823927382-->
+END%%
+
+%%ANKI
+Basic
+Describe what the following command does in in a single sentence:
+```bash
+$ awk 'END { print NR }' data
+```
+Back: Prints the number of lines in `data`.
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+<!--ID: 1706824091124-->
+END%%
+
+%%ANKI
+Basic
+Describe what the following command does in in a single sentence:
+```bash
+$ awk 'NR % 2 == 0' data
+```
+Back: Prints every even-numbered line in `data`.
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+<!--ID: 1706824091128-->
+END%%
+
+## References
+
+* Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)

notes/journal/2024-02-01.md

@@ -0,0 +1,18 @@
+---
+title: "2024-02-01"
+---
+
+- [x] Anki Flashcards
+- [x] KoL
+- [x] Sheet Music (10 min.)
+- [x] OGS (1 Life & Death Problem)
+- [x] Korean (Read 1 Story)
+- [ ] Interview Prep (1 Practice Problem)
+- [x] Log Work Hours (Max 3 hours)
+
+* Today was the first day using the FSRS algorithm with Anki. Continuing to use Just "Again" and "Good" on my original deck and using all options when using the Obsidian-generated deck. Goal is to eventually migrate back to using all the options.
+* Spent some time migrating the Quartz setup to use Nix instead. I lose the ability to run Quartz locally (at least without more work), but upgrades are significantly easier. Theoretically the only thing I should care about is that my notes look good in Markdown/Obsidian anyways so fine with this trade-off.
+* Read 해님 달님 (The Sun and the Moon) from Korean stories.
+* Read sections 11.2 and 13.6 of "Database System Concepts".
+* Practiced [reverse keyboard identification](https://www.musictheory.net/exercises/keyboard-reverse).
+* Spent time learning how Nix's `callpackage` function works.

notes/nix/callPackage.md

@@ -0,0 +1,116 @@
+---
+title: callPackage
+TARGET DECK: Obsidian::STEM
+FILE TAGS: nix
+tags:
+  - nix
+---
+
+## Overview
+
+We first examine `lib.makeOverridable`. It's implementation isn't too important but understanding how it's used is. We adapt the example found in [nixpkgs](https://github.com/NixOS/nixpkgs/blob/56df668386ac83c5bcddf9849c645cf0d25706d7/lib/customisation.nix#L77):
+
+```nix
+nix-repl> x = {a, b}: { example = a + b; }
+nix-repl> y = lib.makeOverridable x { a = 1; b = 2; }
+nix-repl> y
+{ override = «lambda»; overrideDerivation = «lambda»; example = 3; }
+nix-repl> y.override { a = 10; }
+{ override = «lambda»; overrideDerivation = «lambda»; example = 12; }
+```
+
+`lib.makeOverridable` is an example of partial function application. Notice `y` still contains the result (`example`) of evaluating `x`. We can re-run the computation with a different value (in this case `a`) by invoking `y.override`.
+
+%%ANKI
+Basic
+What is the result of the following?
+```nix
+x = {a, b}: { example = a + b; }
+lib.functionArgs x
+```
+Back: `{ a = false; b = false; }`
+Reference: Yin, Ryan. “NixOS and Flakes Book.” Nix, February 1, 2024. [https://github.com/ryan4yin/nixos-and-flakes-book](https://github.com/ryan4yin/nixos-and-flakes-book)
+<!--ID: 1706828138583-->
+END%%
+
+%%ANKI
+Basic
+What does each boolean returned by `lib.functionArgs` indicate?
+Back: Whether the associated attribute has a default value.
+Reference: Yin, Ryan. “NixOS and Flakes Book.” Nix, February 1, 2024. [https://github.com/ryan4yin/nixos-and-flakes-book](https://github.com/ryan4yin/nixos-and-flakes-book)
+<!--ID: 1706828138588-->
+END%%
+
+%%ANKI
+Basic
+What additional attributes is included in the set returned by `lib.makeOverridable`?
+Back: `override` and `overrideDerivation`.
+Reference: Yin, Ryan. “NixOS and Flakes Book.” Nix, February 1, 2024. [https://github.com/ryan4yin/nixos-and-flakes-book](https://github.com/ryan4yin/nixos-and-flakes-book)
+<!--ID: 1706828138590-->
+END%%
+
+%%ANKI
+Basic
+What is the value of `y.example` in the following?
+```nix
+x = {a, b}: { example = a + b; }
+y = lib.makeOverridable x { a = 1; b = 2; }
+```
+Back: `3`
+Reference: Yin, Ryan. “NixOS and Flakes Book.” Nix, February 1, 2024. [https://github.com/ryan4yin/nixos-and-flakes-book](https://github.com/ryan4yin/nixos-and-flakes-book)
+<!--ID: 1706828225233-->
+END%%
+
+%%ANKI
+Basic
+What is the value of `(y.override { a = 10; }).example` in the following?
+```nix
+x = {a, b}: { example = a + b; }
+y = lib.makeOverridable x { a = 1; b = 2; }
+```
+Back: `12`
+Reference: Yin, Ryan. “NixOS and Flakes Book.” Nix, February 1, 2024. [https://github.com/ryan4yin/nixos-and-flakes-book](https://github.com/ryan4yin/nixos-and-flakes-book)
+<!--ID: 1706828225236-->
+END%%
+
+Now we can understand how `pkgs.callPackage` works. The following is a simplification of the [actual implementation](https://github.com/NixOS/nixpkgs/blob/56df668386ac83c5bcddf9849c645cf0d25706d7/lib/customisation.nix#L153):
+
+```nix
+callPackageWith = autoArgs: fn: args:
+  let
+    f = if isFunction fn then fn else import fn;
+    fargs = functionArgs f;
+    allArgs = intersectArgs fargs autoArgs // args;
+  in
+    lib.makeOverridable f allArgs
+
+callPackage = callPackageWith pkgs;
+```
+
+%%ANKI
+Basic
+What two functions is `callPackage` implemented on top of?
+Back: `callPackageWith` and `lib.makeOverridable`.
+Reference: Yin, Ryan. “NixOS and Flakes Book.” Nix, February 1, 2024. [https://github.com/ryan4yin/nixos-and-flakes-book](https://github.com/ryan4yin/nixos-and-flakes-book)
+<!--ID: 1706828138592-->
+END%%
+
+%%ANKI
+Basic
+What is the purpose of `callPackage`?
+Back: It calls package functions with arguments automatic supplied if not overridden. 
+Reference: Yin, Ryan. “NixOS and Flakes Book.” Nix, February 1, 2024. [https://github.com/ryan4yin/nixos-and-flakes-book](https://github.com/ryan4yin/nixos-and-flakes-book)
+<!--ID: 1706828138594-->
+END%%
+
+%%ANKI
+Basic
+What attribute must be invoked in `callPackage`'s return value to override arguments?
+Back: `override`
+Reference: Yin, Ryan. “NixOS and Flakes Book.” Nix, February 1, 2024. [https://github.com/ryan4yin/nixos-and-flakes-book](https://github.com/ryan4yin/nixos-and-flakes-book)
+<!--ID: 1706828225240-->
+END%%
+
+## Reference
+
+* Yin, Ryan. “NixOS and Flakes Book.” Nix, February 1, 2024. [https://github.com/ryan4yin/nixos-and-flakes-book](https://github.com/ryan4yin/nixos-and-flakes-book)

notes/nix/index.md

@@ -0,0 +1,3 @@
+---
+title: Nix
+---

notes/posix/signals.md

@@ -7,7 +7,9 @@ tags:
   - signal
 ---
 
-This is an overview of specific POSIX signals.[^dowling]
+## Overview
+
+This is an overview of specific POSIX signals.
 
 Code  | Name
 ----- | --------------
@@ -112,4 +114,33 @@ Reference: `man 1 ps`
 <!--ID: 1706670390919-->
 END%%
 
-[^dowling]: Dowling, “A List of Signals and What They Mean.”
+### SIGINT (2)
+
+Indicates the process was interrupted by the user. Happens when pressing `Ctrl-C` from the controlling terminal.
+
+%%ANKI
+Cloze
+Signal {`SIGINT`} corresponds to number {2}.
+Reference: Dowling, “A List of Signals and What They Mean.”
+<!--ID: 1706815743860-->
+END%%
+
+%%ANKI
+Basic
+What control sequence usually triggers a `SIGINT`?
+Back: `Ctrl-C`
+Reference: Dowling, “A List of Signals and What They Mean.”
+<!--ID: 1706815743867-->
+END%%
+
+%%ANKI
+Basic
+What is the `INT` in `SIGINT` short for?
+Back: **Int**errupt
+Reference: Dowling, “A List of Signals and What They Mean.”
+<!--ID: 1706815743870-->
+END%%
+
+## References
+
+* Dowling, “A List of Signals and What They Mean.”