152 lines
2.4 KiB
Plaintext
152 lines
2.4 KiB
Plaintext
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# Conversion
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## Convert a hex color to RGB
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**Example Function:**
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```sh
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hex_to_rgb() {
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# Usage: hex_to_rgb "#FFFFFF"
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((r=16#${1:1:2}))
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((g=16#${1:3:2}))
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((b=16#${1:5:6}))
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printf '%s\n' "$r $g $b"
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}
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```
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**Example Usage:**
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```shell
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$ hex_to_rgb "#FFFFFF"
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255 255 255
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```
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## Convert an RGB color to hex
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**Example Function:**
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```sh
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rgb_to_hex() {
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# Usage: rgb_to_hex "r" "g" "b"
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printf '#%02x%02x%02x\n' "$1" "$2" "$3"
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}
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```
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**Example Usage:**
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```shell
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$ rgb_to_hex "255" "255" "255"
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#FFFFFF
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```
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# Code Golf
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## Shorter `for` loop syntax
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```shell
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# Tiny C Style.
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for((;i++<10;)){ echo "$i";}
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# Undocumented method.
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for i in {1..10};{ echo "$i";}
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# Expansion.
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for i in {1..10}; do echo "$i"; done
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# C Style.
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for((i=0;i<=10;i++)); do echo "$i"; done
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```
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## Shorter infinite loops
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```shell
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# Normal method
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while :; do echo hi; done
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# Shorter
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for((;;)){ echo hi;}
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```
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## Shorter function declaration
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```shell
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# Normal method
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f(){ echo hi;}
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# Using a subshell
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f()(echo hi)
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# Using arithmetic
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# You can use this to assign integer values.
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# Example: f a=1
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# f a++
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f()(($1))
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# Using tests, loops etc.
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# NOTE: You can also use ‘while’, ‘until’, ‘case’, ‘(())’, ‘[[]]’.
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f()if true; then echo "$1"; fi
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f()for i in "$@"; do echo "$i"; done
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```
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## Shorter `if` syntax
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```shell
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# One line
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# Note: The 3rd statement may run when the 1st is true
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[[ "$var" == hello ]] && echo hi || echo bye
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[[ "$var" == hello ]] && { echo hi; echo there; } || echo bye
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# Multi line (no else, single statement)
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# Note: The exit status may not be the same as with an if statement
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[[ "$var" == hello ]] && \
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echo hi
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# Multi line (no else)
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[[ "$var" == hello ]] && {
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echo hi
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# ...
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}
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```
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## Simpler `case` statement to set variable
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We can use the `:` builtin to avoid repeating `variable=` in a case
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statement. The `$_` variable stores the last argument of the last
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successful command. `:` always succeeds so we can abuse it to store the
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variable value.
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```shell
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# Modified snippet from Neofetch.
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case "$OSTYPE" in
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"darwin"*)
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: "MacOS"
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;;
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"linux"*)
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: "Linux"
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;;
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*"bsd"* | "dragonfly" | "bitrig")
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: "BSD"
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;;
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"cygwin" | "msys" | "win32")
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: "Windows"
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;;
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*)
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printf '%s\n' "Unknown OS detected, aborting..." >&2
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exit 1
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;;
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esac
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# Finally, set the variable.
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os="$_"
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```
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<!-- CHAPTER END -->
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