Add notes on POSIX regexps.

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

@@ -16,12 +16,39 @@
       "Image Occlusion": "Occlusion",
       "Image Occlusion Enhanced": "ID (hidden)"
     },
-    "CONTEXT_FIELDS": {},
+    "CONTEXT_FIELDS": {
-    "FOLDER_DECKS": {},
+      "Basic": "Context",
-    "FOLDER_TAGS": {},
+      "Cloze": "Context"
+    },
+    "FOLDER_DECKS": {
+      "algorithms": "",
+      "bash": "",
+      "c": "",
+      "gawk": "",
+      "journal": "",
+      "logic": "",
+      "lua": "",
+      "nix": "",
+      "posix": "",
+      "templates": "",
+      "algorithms/sorting": ""
+    },
+    "FOLDER_TAGS": {
+      "algorithms": "",
+      "bash": "",
+      "c": "",
+      "gawk": "",
+      "journal": "",
+      "logic": "",
+      "lua": "",
+      "nix": "",
+      "posix": "",
+      "templates": "",
+      "algorithms/sorting": ""
+    },
     "Syntax": {
-      "Begin Note": "START",
+      "Begin Note": "%%ANKI",
-      "End Note": "END",
+      "End Note": "END%%",
       "Begin Inline Note": "STARTI",
       "End Inline Note": "ENDI",
       "Target Deck Line": "TARGET DECK",
@@ -31,13 +58,13 @@
     },
     "Defaults": {
       "Scan Directory": "",
-      "Tag": "Obsidian_to_Anki",
+      "Tag": "",
-      "Deck": "Default",
+      "Deck": "Obsidian",
       "Scheduling Interval": 0,
       "Add File Link": false,
-      "Add Context": false,
+      "Add Context": true,
-      "CurlyCloze": false,
+      "CurlyCloze": true,
-      "CurlyCloze - Highlights to Clozes": false,
+      "CurlyCloze - Highlights to Clozes": true,
       "ID Comments": true,
       "Add Obsidian Tags": false
     },
@@ -53,10 +80,10 @@
     "bash/index.md": "3b5296277f095acdf16655adcdf524af",
     "bash/prompts.md": "61cb877e68da040a15b85af76b1f68ba",
     "bash/quoting.md": "b1d8869a91001f8b22f0cdc54d806f61",
-    "bash/robustness.md": "a1d0d334939b54cca4bdfd2fd8ca27f0",
+    "bash/robustness.md": "7ab094b95ba2bfa885adba8e9efedf68",
     "bash/shebang.md": "9006547710f9a079a3666169fbeda7aa",
     "c/escape-sequences.md": "07f0811b0fff14f54f78abc33f2e6606",
-    "c/index.md": "d41d8cd98f00b204e9800998ecf8427e",
+    "c/index.md": "aa8a34c62e7bc284ff589e28609222dc",
     "gawk/index.md": "0263448c8ae1ecfc0eacc4788f8402e9",
     "gawk/variables.md": "4482c297e7f4f5987f42f1926a880ca7",
     "index.md": "e48e895feeed7046425bb2ee15419770",
@@ -64,14 +91,17 @@
     "journal/2024-02-01.md": "3aa232387d2dc662384976fd116888eb",
     "journal/2024-02-02.md": "a3b222daee8a50bce4cbac699efc7180",
     "journal/2024-02-03.md": "c6d411f0e2e964270399dd3a99f48382",
-    "logic/index.md": "d41d8cd98f00b204e9800998ecf8427e",
+    "logic/index.md": "3084b41fe1451259a0cf3e54560c2e85",
     "logic/propositional.md": "45aee8bf688aa8fef4b136145085d38a",
-    "lua/index.md": "d41d8cd98f00b204e9800998ecf8427e",
+    "lua/index.md": "26632dae1f852519e2f1af11d65c34eb",
     "nix/callPackage.md": "59796c480e2856fa7491f62ceb7e3c9c",
     "nix/index.md": "dd5ddd19e95d9bdbe020c68974d77a33",
     "posix/index.md": "f7b1ae55f8f5e8f50f89738b1aca9111",
     "posix/signals.md": "2120ddd933fc0d57abb93c33f639afd8",
-    "templates/daily.md": "7866014e730e85683155207a02e367d8"
+    "templates/daily.md": "7866014e730e85683155207a02e367d8",
+    "posix/regexp.md": "d7effae06677d559b15180ce30f1d306",
+    "journal/2024-02-04.md": "e2b5678fc53d7284b71ed6820c02b954",
+    "gawk/regexp.md": "2dbc2548ed9212ddac8e8f66d979b5b7"
   },
   "fields_dict": {
     "Basic": [

notes/bash/robustness.md

@@ -60,6 +60,7 @@ It's interesting to think what else can be used as a measure of a command's robu
 	* Perhaps a program waits a specified amount of time before input is available. The command's success is now externally determined.
 * Locale-aware functionality
 	* Consider for instance [[gawk/index|gawk]]'s `\u` [[escape-sequences|sequence]] which targets characters in the current locale's character set as opposed to specifically Unicode.
+	* POSIX standard [[posix/regexp#Character Classes|character classes]] serve as another example.
 
 The above scenarios are what makes something like [[nix/index|nix]] so compelling.
 

notes/gawk/regexp.md

@@ -0,0 +1,25 @@
+---
+title: Regular Expressions
+TARGET DECK: Obsidian::STEM
+FILE TAGS: linux::cli gawk regexp
+tags:
+  - gawk
+---
+
+## Overview
+
+Most `awk` patterns are regular expressions delimited with `/`. We can use `~` and `!~` to perform more complicated regexp filtering:
+
+```bash
+# Matches any line with `li` somewhere.
+$ awk '/li/' data
+$ awk `$0 ~ /li/` data
+# Matches any line with `li` somewhere in the first field.
+$ awk '$1 ~ /li/' data
+```
+
+`awk`'s implementation of regexps are a superset of [[posix/regexp|POSIX EREs]].
+
+## 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/2024-02-04.md

@@ -0,0 +1,11 @@
+---
+title: "2024-02-04"
+---
+
+- [ ] Anki Flashcards
+- [x] KoL
+- [ ] Sheet Music (10 min.)
+- [ ] OGS (1 Life & Death Problem)
+- [ ] Korean (Read 1 Story)
+- [ ] Interview Prep (1 Practice Problem)
+- [ ] Log Work Hours (Max 3 hours)

notes/posix/regexp.md

@@ -0,0 +1,279 @@
+---
+title: Regular Expressions
+TARGET DECK: Obsidian::STEM
+FILE TAGS: regexp
+tags:
+  - regexp
+---
+
+## Overview
+
+The following ERE (**E**xtended **R**egular **E**xpression) operators were defined to achieve consistency between programs like `grep`, `sed`, and `awk`.
+
+%%ANKI
+Basic
+What is the POSIX ERE standard?
+Back: The **E**xtended **R**egular **E**xpression standard. A standard based off of regexps accepted by `egrep`.
+Reference: “POSIX Basic Regular Expressions,” accessed February 4, 2024, [https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions](https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions).
+<!--ID: 1707050923589-->
+END%%
+
+* `.` matches any single character.
+	* There exist application-specific exclusions. For instance, newlines and the `NUL` character are often ignored.
+
+%%ANKI
+Cloze
+The {`.`} operator matches {any single character}.
+Reference: “POSIX Basic Regular Expressions,” accessed February 4, 2024, [https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions](https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions).
+<!--ID: 1707050923593-->
+END%%
+
+%%ANKI
+Basic
+What two common exclusions are made with `.`?
+Back: Newlines and the `NUL` character.
+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: 1707050923596-->
+END%%
+
+* `[...]`, the **bracket expression**, matches any enclosed character.
+	* An optional `-` can be included to denote a range.
+	* `-` is treated literally if its the first or last specified character.
+	* `]` is treated literally if its the first specified character.
+	* `^` complements the set if its the first specified character.
+
+%%ANKI
+Basic
+What name is given to the `[...]` operator?
+Back: The bracket expression.
+Reference: “POSIX Basic Regular Expressions,” accessed February 4, 2024, [https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions](https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions).
+<!--ID: 1707050923600-->
+END%%
+
+%%ANKI
+Basic
+What three characters are interpreted specially in a bracket expression?
+Back: `^`, `-`, and `]`
+Reference: “POSIX Basic Regular Expressions,” accessed February 4, 2024, [https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions](https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions).
+<!--ID: 1707050923605-->
+END%%
+
+%%ANKI
+Basic
+When is `-` interpreted literally in a bracket expression?
+Back: When it is the first or last specified character.
+Reference: “POSIX Basic Regular Expressions,” accessed February 4, 2024, [https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions](https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions).
+<!--ID: 1707050923610-->
+END%%
+
+%%ANKI
+Basic
+When is `^` interpreted literally in a bracket expression?
+Back: When it is not the first specified character.
+Reference: “POSIX Basic Regular Expressions,” accessed February 4, 2024, [https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions](https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions).
+<!--ID: 1707050923615-->
+END%%
+
+%%ANKI
+Basic
+When is `]` interpreted literally in a bracket expression?
+Back: When it is the first specified character.
+Reference: “POSIX Basic Regular Expressions,” accessed February 4, 2024, [https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions](https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions).
+<!--ID: 1707050923621-->
+END%%
+
+* `^` is the leading anchor. It matches the starting position of a string.
+* `$` is the trailing anchor. It matches the ending position of a string.
+
+%%ANKI
+Cloze
+The {`^`} operator matches {the starting position of a string}.
+Reference: “POSIX Basic Regular Expressions,” accessed February 4, 2024, [https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions](https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions).
+<!--ID: 1707050923629-->
+END%%
+
+%%ANKI
+Cloze
+The {`$`} operator matches {the ending position of a string}.
+Reference: “POSIX Basic Regular Expressions,” accessed February 4, 2024, [https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions](https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions).
+<!--ID: 1707050923635-->
+END%%
+
+%%ANKI
+Basic
+`^` and `$` belong to what operator category?
+Back: Anchors
+Reference: “POSIX Basic Regular Expressions,” accessed February 4, 2024, [https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions](https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions).
+<!--ID: 1707050923643-->
+END%%
+
+* `*` matches the preceding element zero or more times.
+* `+` matches the preceding element one or more times.
+* `?` matches the preceding element zero or one times.
+
+%%ANKI
+Basic
+What does the `*` operator do?
+Back: Matches the preceding element zero or more times.
+Reference: “POSIX Basic Regular Expressions,” accessed February 4, 2024, [https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions](https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions).
+<!--ID: 1707050923650-->
+END%%
+
+%%ANKI
+Basic
+What does the `+` operator do?
+Back: Matches the preceding element one or more times.
+Reference: “POSIX Basic Regular Expressions,” accessed February 4, 2024, [https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions](https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions).
+<!--ID: 1707050923656-->
+END%%
+
+%%ANKI
+Basic
+What does the `?` operator do?
+Back: Matches the preceding element zero or one times.
+Reference: “POSIX Basic Regular Expressions,” accessed February 4, 2024, [https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions](https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions).
+<!--ID: 1707050923662-->
+END%%
+
+* `{n}`, an **interval expression**, matches the preceding element `n` times.
+	* `{n,}` matches the preceding element at least `n` times.
+	* `{n,m}` matches the preceding element between `n` and `m` times.
+	* Interval expressions cannot contain repetition counts `> 255`. Results are otherwise undefined.
+
+%%ANKI
+Basic
+What name is given to the e.g. `{n,m}` operator?
+Back: The interval expression.
+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: 1707050923669-->
+END%%
+
+%%ANKI
+Basic
+What does the `{n}` operator do?
+Back: Matches the preceding element `n` times.
+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: 1707050923676-->
+END%%
+
+%%ANKI
+Basic
+What does the `{n,}` operator do?
+Back: Matches the preceding element at least `n` times.
+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: 1707050923683-->
+END%%
+
+%%ANKI
+Basic
+What does the `{n,m}` operator do?
+Back: Matches the preceding element between `n` and `m` times.
+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: 1707050923689-->
+END%%
+
+%%ANKI
+Basic
+What interval expression repetition counts lead to undefined behavior?
+Back: Counts greater than `255`.
+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: 1707050923695-->
+END%%
+
+* `|` is the **alternation operator**. It allows specifying match alternatives.
+
+%%ANKI
+Basic
+What name is given to the e.g. `|` operator?
+Back: The alternation operator.
+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: 1707050923701-->
+END%%
+
+%%ANKI
+Basic
+What does the `|` operator do?
+Back: Matches different regexp alternatives.
+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: 1707050923708-->
+END%%
+
+%%ANKI
+Basic
+Which regexp operator has the least precedence?
+Back: `|`
+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: 1707050923713-->
+END%%
+
+## Character Classes
+
+Notation for describing a class of characters specific to a given locale/character set.
+
+%%ANKI
+Basic
+What inconsistency do character classes introduce?
+Back: Matching characters are dependent on locale/character set.
+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: 1707050923719-->
+END%%
+
+%%ANKI
+Basic
+How are character classes denoted?
+Back: `[:class:]`
+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: 1707050923724-->
+END%%
+
+Class        | Similar To      | Meaning
+------------ | --------------- | ------------------------------------------------
+`[:alnum:]`  | `[A-Za-z0-9]`   | Alphanumeric characters
+`[:alpha:]`  | `[A-Za-z]`      | Alphabetic characters
+`[:blank:]`  | `[ \t]`         | `' '` and `TAB` characters
+`[:cntrl:]`  |                 | Control characters
+`[:digit:]`  | `[0-9]`         | Numeric characters
+`[:graph:]`  | `[^ [:cntrl:]]` | Printable and visible characters
+`[:lower:]`  | `[a-z]`         | Lowercase alphabetic characters
+`[:print:]`  | `[ [:graph:]]`  | Printable characters
+`[:punct:]`  |                 | All graphic characters except letters and digits
+`[:space:]`  | `[ \t\n\r\f\v]` | Whitespace characters
+`[:upper:]`  | `[A-Z]`         | Uppercase alphabetic characters
+`[:xdigit:]` | `[0-9A-Fa-f]`   | Hexadecimal digits
+
+%%ANKI
+Basic
+Generally speaking, what is a printable character?
+Back: Characters that can be displayed on screen or printed on paper.
+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: 1707050923728-->
+END%%
+
+%%ANKI
+Basic
+Is `'a'` (i.e. the letter *a*) printable and/or visible?
+Back: It is printable and visible.
+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: 1707050923732-->
+END%%
+
+%%ANKI
+Basic
+Is `' '` (i.e. the space character) printable and/or visible?
+Back: It is printable but not visible.
+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: 1707050923736-->
+END%%
+
+%%ANKI
+Basic
+Is `'\t'` (i.e. the tab character) printable and/or visible?
+Back: It is neither printable nor visible.
+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: 1707050923740-->
+END%%
+
+## References
+
+* “POSIX Basic Regular Expressions,” accessed February 4, 2024, [https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions](https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions).
+* 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)