add shell slides

slides/shells/shells.md

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+# Origin
+
+- Used as a 'shell' around a bare-ass kernel.
+- People once considered a basic shell user-friendly.
+
+## Use Cases
+
+- It's crazy-fast
+- Try deleting a file in Python.
+
+## Form
+
+- Big mess of binaries, wrapped together
+- Janky mess
+
+# Bangs!
+
+Don't say `#!/bin/bash` if you don't mean it!
+
+| Bang!          | Apraisal      |
+|:---------------|:--------------|
+| `#!/bin/bash`  | reasonable    |
+| `#!/bin/sh`    | sensible      |
+| `#!/bin/dash`  | bad idea      |
+| `#!/bin/zsh`   | risky         |
+| `#!/bin/ksh`   | foolish       |
+| `#!/bin/fish`  | madness       |
+| `#!/bin/elvish`| genius        |
+
+Protip: for a faster machine, make `sh` a link to `/bin/dash`.
+
+`ln -s /bin/dash /bin/dash`
+
+# Deviant Shells
+
+## `ksh` (korn shell)
+
+- Can be posix compliant with effort.
+- vi mode by default.
+
+## `elvish`
+
+- pure style
+- built-in browser
+- Ctrl+i to search for commands in $PATH
+- Ctrl+n to search for command arguments
+- Ctrl+l to return to previous locations
+
+## Bash Advantages
+
+- Equality check with "==".
+    * Dash cannot do `if [ $x == 3 ]; then echo y; fi`
+- `$RANDOM`
+- Dash cannot use `&>/dev/null`
+- No history
+
+# Protips
+
+```
+"\C- ": shell-expand-line
+"\C-x": glob-expand-word
+```
+
+- `set -o vi`
+- Ctrl+d
+- `type $whatevre`
+- `.inputrc`
+
+# Fun with Bash
+
+- wifi_qr.sh
+- clean.sh
+- theme.sh
+
+# Zen Master Foo
+
+Master Foo once said to a visiting programmer: "There is more Unix-nature in one line of shell script than there is in ten thousand lines of C."
+
+The programmer, who was very proud of his mastery of C, said: "How can this be?
+C is the language in which the very kernel of Unix is implemented!"
+
+Master Foo replied: "That is so.
+Nevertheless, there is more Unix-nature in one line of shell script than there is in ten thousand lines of C."
+
+# 
+
+The programmer grew distressed. "But through the C language we experience the enlightenment of the Patriarch Ritchie! We become as one with the operating system and the machine, reaping matchless performance!"
+
+Master Foo replied: "All that you say is true.
+But there is still more Unix-nature in one line of shell script than there is in ten thousand lines of C."
+
+The programmer scoffed at Master Foo and rose to depart.
+But Master Foo nodded to his student Nubi, who wrote a line of shell script on a nearby whiteboard, and said: "Master programmer, consider this pipeline.
+Implemented in pure C, would it not span ten thousand lines?"
+
+# 
+
+The programmer muttered through his beard, contemplating what Nubi had written.
+Finally he agreed that it was so.
+
+"And how many hours would you require to implement and debug that C program?" asked Nubi.
+
+"Many," admitted the visiting programmer. "But only a fool would spend the time to do that when so many more worthy tasks await him."
+
+"And who better understands the Unix-nature?" Master Foo asked. "Is it he who writes the ten thousand lines, or he who,
+perceiving the emptiness of the task, gains merit by not coding?"
+
+Upon hearing this, the programmer was enlightened.
+