Added arithmetic operators
This commit is contained in:
Dylan Araps
@@ -1,189 +1,147 @@
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# OTHER
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# CONVERSION
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## Use `read` as an alternative to the `sleep` command
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Surprisingly, `sleep` is an external command and not a `bash` built-in.
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**CAVEAT:** Requires `bash` 4+
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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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read_sleep() {
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# Usage: sleep 1
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# sleep 0.2
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read -rst "${1:-1}" -N 999
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hex_to_rgb() {
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# Usage: hex_to_rgb "#FFFFFF"
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((r=16#${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 $b"
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}
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```
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**Example Usage:**
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```shell
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read_sleep 1
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read_sleep 0.1
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read_sleep 30
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$ hex_to_rgb "#FFFFFF"
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255 255 255
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```
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## Check if a program is in the user's PATH
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```shell
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# There are 3 ways to do this and either one can be used.
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type -p executable_name &>/dev/null
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hash executable_name &>/dev/null
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command -v executable_name &>/dev/null
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# As a test.
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if type -p executable_name &>/dev/null; then
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# Program is in PATH.
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fi
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# Inverse.
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if ! type -p executable_name &>/dev/null; then
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# Program is not in PATH.
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fi
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# Example (Exit early if program is not installed).
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if ! type -p convert &>/dev/null; then
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printf '%s\n' "error: convert is not installed, exiting..."
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exit 1
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fi
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```
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## Get the current date using `strftime`
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Bash’s `printf` has a built-in method of getting the date which can be used in place of the `date` command.
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**CAVEAT:** Requires `bash` 4+
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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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date() {
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# Usage: date "format"
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# See: 'man strftime' for format.
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printf "%($1)T\\n" "-1"
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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" "$3"
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}
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```
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**Example Usage:**
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```shell
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# Using above function.
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$ date "%a %d %b - %l:%M %p"
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Fri 15 Jun - 10:00 AM
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# Using printf directly.
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$ printf '%(%a %d %b - %l:%M %p)T\n' "-1"
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Fri 15 Jun - 10:00 AM
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# Assigning a variable using printf.
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$ printf -v date '%(%a %d %b - %l:%M %p)T\n' '-1'
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$ printf '%s\n' "$date"
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Fri 15 Jun - 10:00 AM
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$ rgb_to_hex "255" "255" "255"
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#FFFFFF
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```
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## Generate a UUID V4
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**Example Function:**
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# CODE GOLF
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```sh
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uuid() {
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# Usage: uuid
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C="89ab"
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## Shorter `for` loop syntax
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for ((N=0;N<16;++N)); do
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B="$((RANDOM%256))"
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```shell
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# Tiny C Style.
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for((;i++<10;)){ echo "$i";}
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case "$N" in
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6) printf '4%x' "$((B%16))" ;;
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8) printf '%c%x' "${C:$RANDOM%${#C}:1}" "$((B%16))" ;;
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# Undocumented method.
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for i in {1..10};{ echo "$i";}
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3|5|7|9)
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printf '%02x-' "$B"
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;;
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# Expansion.
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for i in {1..10}; do echo "$i"; done
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*)
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printf '%02x' "$B"
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;;
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esac
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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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printf '\n'
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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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# This can be used 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: ‘while’, ‘until’, ‘case’, ‘(())’, ‘[[]]’ can also be used.
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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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[[ "$var" == hello ]] && {
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echo hi
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# ...
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}
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```
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**Example Usage:**
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## Simpler `case` statement to set variable
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The `:` built-in can be used to avoid repeating `variable=` in a case statement. The `$_` variable stores the last argument of the last command. `:` always succeeds so it can be used to store the variable value.
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```shell
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$ uuid
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d5b6c731-1310-4c24-9fe3-55d556d44374
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```
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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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## Progress bars
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"linux"*)
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: "Linux"
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;;
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This is a simple way of drawing progress bars without needing a for loop
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in the function itself.
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*"bsd"* | "dragonfly" | "bitrig")
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: "BSD"
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;;
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**Example Function:**
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"cygwin" | "msys" | "win32")
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: "Windows"
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;;
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```sh
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bar() {
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# Usage: bar 1 10
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# ^----- Elapsed Percentage (0-100).
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# ^-- Total length in chars.
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((elapsed=$1*$2/100))
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*)
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printf '%s\n' "Unknown OS detected, aborting..." >&2
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exit 1
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;;
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esac
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# Create the bar with spaces.
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printf -v prog "%${elapsed}s"
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printf -v total "%$(($2-elapsed))s"
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printf '%s\r' "[${prog// /-}${total}]"
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}
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```
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**Example Usage:**
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```shell
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for ((i=0;i<=100;i++)); do
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# Pure bash micro sleeps (for the example).
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(:;:) && (:;:) && (:;:) && (:;:) && (:;:)
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# Print the bar.
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bar "$i" "10"
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done
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printf '\n'
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```
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## Get the list of functions in a script
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```sh
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get_functions() {
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# Usage: get_functions
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IFS=$'\n' read -d "" -ra functions < <(declare -F)
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printf '%s\n' "${functions[@]//declare -f }"
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}
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```
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## Bypass shell aliases
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```shell
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# alias
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ls
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# command
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# shellcheck disable=SC1001
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\ls
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```
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## Bypass shell functions
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```shell
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# function
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ls
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# command
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command ls
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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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