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Added arithmetic operators

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This commit is contained in:
Dylan Araps
2018-06-21 18:00:05 +10:00
parent b5a2ad5e0a
commit 955370b5ce
11 changed files with 621 additions and 497 deletions
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67
README.md
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@@ -93,7 +93,13 @@ See something that is incorrectly described, buggy or outright wrong? Open an is
* [BRACE EXPANSION](#brace-expansion)
* [Ranges](#ranges)
* [String Lists](#string-lists)
* [ARITHMETIC](#arithmetic)
* [ARITHMETIC OPERATORS](#arithmetic-operators)
* [Assignment](#assignment)
* [Arithmetic](#arithmetic)
* [Bitwise](#bitwise)
* [Logical](#logical)
* [Miscellaneous](#miscellaneous)
* [ARITHMETIC](#arithmetic-1)
* [Simpler syntax to set variables](#simpler-syntax-to-set-variables)
* [Ternary Tests](#ternary-tests)
* [TRAPS](#traps)
@@ -1189,6 +1195,65 @@ echo {apples,oranges,pears,grapes}
rm -rf ~/Downloads/{Movies,Music,ISOS}
```
<!-- CHAPTER END -->
<!-- CHAPTER START -->
# ARITHMETIC OPERATORS
## Assignment
| Operators | What does it do? |
| --------- | ---------------- |
| `=` | Initialize or change the value of a variable.
## Arithmetic
| Operators | What does it do? |
| --------- | ---------------- |
| `+` | Addition
| `-` | Subtraction
| `*` | Multiplication
| `/` | Division
| `**` | Exponentiation
| `%` | Modulo
| `+=` | Plus-Equal (*Increment a variable.*)
| `-=` | Minus-Equal (*Decrement a variable.*)
| `*=` | Times-Equal (*Multiply a variable.*)
| `/=` | Slash-Equal (*Divide a variable.*)
| `%=` | Mod-Equal (*Remainder of dividing a variable.*)
## Bitwise
| Operators | What does it do? |
| --------- | ---------------- |
| `<<` | Bitwise Left Shift
| `<<=` | Left-Shift-Equal
| `>>` | Bitwise Right Shift
| `>>=` | Right-Shift-Equal
| `&` | Bitwise AND
| `&=` | Bitwise AND-Equal
| `\|` | Bitwise OR
| `\|=` | Bitwise OR-Equal
| `~` | Bitwise NOT
| `^` | Bitwise XOR
| `^=` | Bitwise XOR-Equal
## Logical
| Operators | What does it do? |
| --------- | ---------------- |
| `!` | NOT
| `&&` | AND
| `\|\|` | OR
## Miscellaneous
| Operators | What does it do? | Example |
| --------- | ---------------- | ------- |
| `,` | Comma Separator | `((a=1,b=2,c=3))`
<!-- CHAPTER END -->
<!-- CHAPTER START -->

1
manuscript/Book.txt
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@@ -16,3 +16,4 @@ chapter14.txt
chapter15.txt
chapter16.txt
chapter17.txt
chapter18.txt

71
manuscript/chapter10.txt
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@@ -1,31 +1,58 @@
# ARITHMETIC
## Simpler syntax to set variables
# ARITHMETIC OPERATORS
```shell
# Simple math
((var=1+2))
## Assignment
# Decrement/Increment variable
((var++))
((var--))
((var+=1))
((var-=1))
| Operators | What does it do? |
| --------- | ---------------- |
| `=` | Initialize or change the value of a variable.
# Using variables
((var=var2*arr[2]))
```
## Arithmetic
## Ternary Tests
| Operators | What does it do? |
| --------- | ---------------- |
| `+` | Addition
| `-` | Subtraction
| `*` | Multiplication
| `/` | Division
| `**` | Exponentiation
| `%` | Modulo
| `+=` | Plus-Equal (*Increment a variable.*)
| `-=` | Minus-Equal (*Decrement a variable.*)
| `*=` | Times-Equal (*Multiply a variable.*)
| `/=` | Slash-Equal (*Divide a variable.*)
| `%=` | Mod-Equal (*Remainder of dividing a variable.*)
## Bitwise
| Operators | What does it do? |
| --------- | ---------------- |
| `<<` | Bitwise Left Shift
| `<<=` | Left-Shift-Equal
| `>>` | Bitwise Right Shift
| `>>=` | Right-Shift-Equal
| `&` | Bitwise AND
| `&=` | Bitwise AND-Equal
| `\|` | Bitwise OR
| `\|=` | Bitwise OR-Equal
| `~` | Bitwise NOT
| `^` | Bitwise XOR
| `^=` | Bitwise XOR-Equal
## Logical
| Operators | What does it do? |
| --------- | ---------------- |
| `!` | NOT
| `&&` | AND
| `\|\|` | OR
## Miscellaneous
| Operators | What does it do? | Example |
| --------- | ---------------- | ------- |
| `,` | Comma Separator | `((a=1,b=2,c=3))`
```shell
# Set the value of var to var2 if var2 is greater than var.
# var: variable to set.
# var2>var: Condition to test.
# ?var2: If the test succeeds.
# :var: If the test fails.
((var=var2>var?var2:var))
```
<!-- CHAPTER END -->

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@@ -1,42 +1,30 @@
# TRAPS
# ARITHMETIC
Traps allow a script to execute code on various signals. In [pxltrm](https://github.com/dylanaraps/pxltrm) (*a pixel art editor written in bash*) traps are used to redraw the user interface on window resize. Another use case is cleaning up temporary files on script exit.
Traps should be added near the start of scripts so any early errors are also caught.
**NOTE:** For a full list of signals, see `trap -l`.
## Do something on script exit
## Simpler syntax to set variables
```shell
# Clear screen on script exit.
trap 'printf \\e[2J\\e[H\\e[m' EXIT
# Simple math
((var=1+2))
# Decrement/Increment variable
((var++))
((var--))
((var+=1))
((var-=1))
# Using variables
((var=var2*arr[2]))
```
## Ignore terminal interrupt (CTRL+C, SIGINT)
## Ternary Tests
```shell
trap '' INT
```
## React to window resize.
```shell
# Call a function on window resize.
trap 'code_here' SIGWINCH
```
## Do something before every command.
```shell
trap 'code_here' DEBUG
```
## Do something when a shell function or a sourced file finishes executing
```shell
trap 'code_here' RETURN
# Set the value of var to var2 if var2 is greater than var.
# var: variable to set.
# var2>var: Condition to test.
# ?var2: If the test succeeds.
# :var: If the test fails.
((var=var2>var?var2:var))
```
<!-- CHAPTER END -->

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@@ -1,13 +1,42 @@
# PERFORMANCE
# TRAPS
## Disable Unicode
Traps allow a script to execute code on various signals. In [pxltrm](https://github.com/dylanaraps/pxltrm) (*a pixel art editor written in bash*) traps are used to redraw the user interface on window resize. Another use case is cleaning up temporary files on script exit.
If unicode is not required, it can be disabled for a performance increase. Results may vary however there have been noticeable improvements in [neofetch](https://github.com/dylanaraps/neofetch) and other programs.
Traps should be added near the start of scripts so any early errors are also caught.
**NOTE:** For a full list of signals, see `trap -l`.
## Do something on script exit
```shell
# Disable unicode.
LC_ALL=C
LANG=C
# Clear screen on script exit.
trap 'printf \\e[2J\\e[H\\e[m' EXIT
```
## Ignore terminal interrupt (CTRL+C, SIGINT)
```shell
trap '' INT
```
## React to window resize.
```shell
# Call a function on window resize.
trap 'code_here' SIGWINCH
```
## Do something before every command.
```shell
trap 'code_here' DEBUG
```
## Do something when a shell function or a sourced file finishes executing
```shell
trap 'code_here' RETURN
```
<!-- CHAPTER END -->

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manuscript/chapter13.txt
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@@ -1,51 +1,13 @@
# OBSOLETE SYNTAX
# PERFORMANCE
## Shebang
## Disable Unicode
Use `#!/usr/bin/env bash` instead of `#!/bin/bash`.
- The former searches the user's `PATH` to find the `bash` binary.
- The latter assumes it is always installed to `/bin/` which can cause issues.
If unicode is not required, it can be disabled for a performance increase. Results may vary however there have been noticeable improvements in [neofetch](https://github.com/dylanaraps/neofetch) and other programs.
```shell
# Right:
#!/usr/bin/env bash
# Wrong:
#!/bin/bash
```
## Command Substitution
Use `$()` instead of `` ` ` ``.
```shell
# Right.
var="$(command)"
# Wrong.
var=`command`
# $() can easily be nested whereas `` cannot.
var="$(command "$(command)")"
```
## Function Declaration
Do not use the `function` keyword, it reduces compatibility with older versions of `bash`.
```shell
# Right.
do_something() {
# ...
}
# Wrong.
function do_something() {
# ...
}
# Disable unicode.
LC_ALL=C
LANG=C
```
<!-- CHAPTER END -->

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@@ -1,93 +1,51 @@
# INTERNAL VARIABLES
# OBSOLETE SYNTAX
## Get the location to the `bash` binary
## Shebang
Use `#!/usr/bin/env bash` instead of `#!/bin/bash`.
- The former searches the user's `PATH` to find the `bash` binary.
- The latter assumes it is always installed to `/bin/` which can cause issues.
```shell
"$BASH"
# Right:
#!/usr/bin/env bash
# Wrong:
#!/bin/bash
```
## Get the version of the current running `bash` process
## Command Substitution
Use `$()` instead of `` ` ` ``.
```shell
# As a string.
"$BASH_VERSION"
# Right.
var="$(command)"
# As an array.
"${BASH_VERSINFO[@]}"
# Wrong.
var=`command`
# $() can easily be nested whereas `` cannot.
var="$(command "$(command)")"
```
## Open the user's preferred text editor
## Function Declaration
Do not use the `function` keyword, it reduces compatibility with older versions of `bash`.
```shell
"$EDITOR" "$file"
# Right.
do_something() {
# ...
}
# NOTE: This variable may be empty, set a fallback value.
"${EDITOR:-vi}" "$file"
```
## Get the name of the current function
```shell
# Current function.
"${FUNCNAME[0]}"
# Parent function.
"${FUNCNAME[1]}"
# So on and so forth.
"${FUNCNAME[2]}"
"${FUNCNAME[3]}"
# All functions including parents.
"${FUNCNAME[@]}"
```
## Get the host-name of the system
```shell
"$HOSTNAME"
# NOTE: This variable may be empty.
# Optionally set a fallback to the hostname command.
"${HOSTNAME:-$(hostname)}"
```
## Get the architecture of the Operating System
```shell
"$HOSTTYPE"
```
## Get the name of the Operating System / Kernel
This can be used to add conditional support for different Operating
Systems without needing to call `uname`.
```shell
"$OSTYPE"
```
## Get the current working directory
This is an alternative to the `pwd` built-in.
```shell
"$PWD"
```
## Get the number of seconds the script has been running
```shell
"$SECONDS"
```
## Get a pseudorandom integer
Each time `$RANDOM` is used, a different integer between `0` and `32767` is returned. This variable should not be used for anything related to security (*this includes encryption keys etc*).
```shell
"$RANDOM"
# Wrong.
function do_something() {
# ...
}
```
<!-- CHAPTER END -->

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@@ -1,78 +1,93 @@
# INFORMATION ABOUT THE TERMINAL
# INTERNAL VARIABLES
## Get the terminal size in lines and columns (*from a script*)
This is handy when writing scripts in pure bash and `stty`/`tput` can’t be
called.
**Example Function:**
```sh
get_term_size() {
# Usage: get_term_size
# (:;:) is a micro sleep to ensure the variables are
# exported immediately.
shopt -s checkwinsize; (:;:)
printf '%s\n' "$LINES $COLUMNS"
}
```
**Example Usage:**
## Get the location to the `bash` binary
```shell
# Output: LINES COLUMNS
$ get_term_size
15 55
"$BASH"
```
## Get the terminal size in pixels
**CAVEAT**: This does not work in some terminal emulators.
**Example Function:**
```sh
get_window_size() {
# Usage: get_window_size
printf '%b' "${TMUX:+\\ePtmux;\\e}\\e[14t${TMUX:+\\e\\\\}"
IFS=';t' read -d t -t 0.05 -sra term_size
printf '%s\n' "${term_size[1]}x${term_size[2]}"
}
```
**Example Usage:**
## Get the version of the current running `bash` process
```shell
# Output: WIDTHxHEIGHT
$ get_window_size
1200x800
# As a string.
"$BASH_VERSION"
# Output (fail):
$ get_window_size
x
# As an array.
"${BASH_VERSINFO[@]}"
```
## Get the current cursor position
This is useful when creating a TUI in pure bash.
**Example Function:**
```sh
get_cursor_pos() {
# Usage: get_cursor_pos
IFS='[;' read -p $'\e[6n' -d R -rs _ y x _
printf '%s\n' "$x $y"
}
```
**Example Usage:**
## Open the user's preferred text editor
```shell
# Output: X Y
$ get_cursor_pos
1 8
"$EDITOR" "$file"
# NOTE: This variable may be empty, set a fallback value.
"${EDITOR:-vi}" "$file"
```
## Get the name of the current function
```shell
# Current function.
"${FUNCNAME[0]}"
# Parent function.
"${FUNCNAME[1]}"
# So on and so forth.
"${FUNCNAME[2]}"
"${FUNCNAME[3]}"
# All functions including parents.
"${FUNCNAME[@]}"
```
## Get the host-name of the system
```shell
"$HOSTNAME"
# NOTE: This variable may be empty.
# Optionally set a fallback to the hostname command.
"${HOSTNAME:-$(hostname)}"
```
## Get the architecture of the Operating System
```shell
"$HOSTTYPE"
```
## Get the name of the Operating System / Kernel
This can be used to add conditional support for different Operating
Systems without needing to call `uname`.
```shell
"$OSTYPE"
```
## Get the current working directory
This is an alternative to the `pwd` built-in.
```shell
"$PWD"
```
## Get the number of seconds the script has been running
```shell
"$SECONDS"
```
## Get a pseudorandom integer
Each time `$RANDOM` is used, a different integer between `0` and `32767` is returned. This variable should not be used for anything related to security (*this includes encryption keys etc*).
```shell
"$RANDOM"
```
<!-- CHAPTER END -->

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@@ -1,147 +1,78 @@
# CONVERSION
# INFORMATION ABOUT THE TERMINAL
## Convert a hex color to RGB
## Get the terminal size in lines and columns (*from a script*)
This is handy when writing scripts in pure bash and `stty`/`tput` can’t be
called.
**Example Function:**
```sh
hex_to_rgb() {
# Usage: hex_to_rgb "#FFFFFF"
((r=16#${1:1:2}))
((g=16#${1:3:2}))
((b=16#${1:5:6}))
get_term_size() {
# Usage: get_term_size
printf '%s\n' "$r $g $b"
# (:;:) is a micro sleep to ensure the variables are
# exported immediately.
shopt -s checkwinsize; (:;:)
printf '%s\n' "$LINES $COLUMNS"
}
```
**Example Usage:**
```shell
$ hex_to_rgb "#FFFFFF"
255 255 255
# Output: LINES COLUMNS
$ get_term_size
15 55
```
## Get the terminal size in pixels
## Convert an RGB color to hex
**CAVEAT**: This does not work in some terminal emulators.
**Example Function:**
```sh
rgb_to_hex() {
# Usage: rgb_to_hex "r" "g" "b"
printf '#%02x%02x%02x\n' "$1" "$2" "$3"
get_window_size() {
# Usage: get_window_size
printf '%b' "${TMUX:+\\ePtmux;\\e}\\e[14t${TMUX:+\\e\\\\}"
IFS=';t' read -d t -t 0.05 -sra term_size
printf '%s\n' "${term_size[1]}x${term_size[2]}"
}
```
**Example Usage:**
```shell
$ rgb_to_hex "255" "255" "255"
#FFFFFF
# Output: WIDTHxHEIGHT
$ get_window_size
1200x800
# Output (fail):
$ get_window_size
x
```
## Get the current cursor position
# CODE GOLF
This is useful when creating a TUI in pure bash.
## Shorter `for` loop syntax
**Example Function:**
```shell
# Tiny C Style.
for((;i++<10;)){ echo "$i";}
# Undocumented method.
for i in {1..10};{ echo "$i";}
# Expansion.
for i in {1..10}; do echo "$i"; done
# C Style.
for((i=0;i<=10;i++)); do echo "$i"; done
```
## Shorter infinite loops
```shell
# Normal method
while :; do echo hi; done
# Shorter
for((;;)){ echo hi;}
```
## Shorter function declaration
```shell
# Normal method
f(){ echo hi;}
# Using a subshell
f()(echo hi)
# Using arithmetic
# This can be used to assign integer values.
# Example: f a=1
# f a++
f()(($1))
# Using tests, loops etc.
# NOTE: ‘while’, ‘until’, ‘case’, ‘(())’, ‘[[]]’ can also be used.
f()if true; then echo "$1"; fi
f()for i in "$@"; do echo "$i"; done
```
## Shorter `if` syntax
```shell
# One line
# Note: The 3rd statement may run when the 1st is true
[[ "$var" == hello ]] && echo hi || echo bye
[[ "$var" == hello ]] && { echo hi; echo there; } || echo bye
# Multi line (no else, single statement)
# Note: The exit status may not be the same as with an if statement
[[ "$var" == hello ]] && \
echo hi
# Multi line (no else)
[[ "$var" == hello ]] && {
echo hi
# ...
```sh
get_cursor_pos() {
# Usage: get_cursor_pos
IFS='[;' read -p $'\e[6n' -d R -rs _ y x _
printf '%s\n' "$x $y"
}
```
## Simpler `case` statement to set variable
The `:` built-in can be used to avoid repeating `variable=` in a case statement. The `$_` variable stores the last argument of the last command. `:` always succeeds so it can be used to store the variable value.
**Example Usage:**
```shell
# Modified snippet from Neofetch.
case "$OSTYPE" in
"darwin"*)
: "MacOS"
;;
"linux"*)
: "Linux"
;;
*"bsd"* | "dragonfly" | "bitrig")
: "BSD"
;;
"cygwin" | "msys" | "win32")
: "Windows"
;;
*)
printf '%s\n' "Unknown OS detected, aborting..." >&2
exit 1
;;
esac
# Finally, set the variable.
os="$_"
# Output: X Y
$ get_cursor_pos
1 8
```
<!-- CHAPTER END -->

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@@ -1,189 +1,147 @@
# OTHER
# CONVERSION
## Use `read` as an alternative to the `sleep` command
Surprisingly, `sleep` is an external command and not a `bash` built-in.
**CAVEAT:** Requires `bash` 4+
## Convert a hex color to RGB
**Example Function:**
```sh
read_sleep() {
# Usage: sleep 1
# sleep 0.2
read -rst "${1:-1}" -N 999
hex_to_rgb() {
# Usage: hex_to_rgb "#FFFFFF"
((r=16#${1:1:2}))
((g=16#${1:3:2}))
((b=16#${1:5:6}))
printf '%s\n' "$r $g $b"
}
```
**Example Usage:**
```shell
read_sleep 1
read_sleep 0.1
read_sleep 30
$ hex_to_rgb "#FFFFFF"
255 255 255
```
## Check if a program is in the user's PATH
```shell
# There are 3 ways to do this and either one can be used.
type -p executable_name &>/dev/null
hash executable_name &>/dev/null
command -v executable_name &>/dev/null
# As a test.
if type -p executable_name &>/dev/null; then
# Program is in PATH.
fi
# Inverse.
if ! type -p executable_name &>/dev/null; then
# Program is not in PATH.
fi
# Example (Exit early if program is not installed).
if ! type -p convert &>/dev/null; then
printf '%s\n' "error: convert is not installed, exiting..."
exit 1
fi
```
## Get the current date using `strftime`
Bash’s `printf` has a built-in method of getting the date which can be used in place of the `date` command.
**CAVEAT:** Requires `bash` 4+
## Convert an RGB color to hex
**Example Function:**
```sh
date() {
# Usage: date "format"
# See: 'man strftime' for format.
printf "%($1)T\\n" "-1"
rgb_to_hex() {
# Usage: rgb_to_hex "r" "g" "b"
printf '#%02x%02x%02x\n' "$1" "$2" "$3"
}
```
**Example Usage:**
```shell
# Using above function.
$ date "%a %d %b - %l:%M %p"
Fri 15 Jun - 10:00 AM
# Using printf directly.
$ printf '%(%a %d %b - %l:%M %p)T\n' "-1"
Fri 15 Jun - 10:00 AM
# Assigning a variable using printf.
$ printf -v date '%(%a %d %b - %l:%M %p)T\n' '-1'
$ printf '%s\n' "$date"
Fri 15 Jun - 10:00 AM
$ rgb_to_hex "255" "255" "255"
#FFFFFF
```
## Generate a UUID V4
**Example Function:**
# CODE GOLF
```sh
uuid() {
# Usage: uuid
C="89ab"
## Shorter `for` loop syntax
for ((N=0;N<16;++N)); do
B="$((RANDOM%256))"
```shell
# Tiny C Style.
for((;i++<10;)){ echo "$i";}
case "$N" in
6) printf '4%x' "$((B%16))" ;;
8) printf '%c%x' "${C:$RANDOM%${#C}:1}" "$((B%16))" ;;
# Undocumented method.
for i in {1..10};{ echo "$i";}
3|5|7|9)
printf '%02x-' "$B"
# Expansion.
for i in {1..10}; do echo "$i"; done
# C Style.
for((i=0;i<=10;i++)); do echo "$i"; done
```
## Shorter infinite loops
```shell
# Normal method
while :; do echo hi; done
# Shorter
for((;;)){ echo hi;}
```
## Shorter function declaration
```shell
# Normal method
f(){ echo hi;}
# Using a subshell
f()(echo hi)
# Using arithmetic
# This can be used to assign integer values.
# Example: f a=1
# f a++
f()(($1))
# Using tests, loops etc.
# NOTE: ‘while’, ‘until’, ‘case’, ‘(())’, ‘[[]]’ can also be used.
f()if true; then echo "$1"; fi
f()for i in "$@"; do echo "$i"; done
```
## Shorter `if` syntax
```shell
# One line
# Note: The 3rd statement may run when the 1st is true
[[ "$var" == hello ]] && echo hi || echo bye
[[ "$var" == hello ]] && { echo hi; echo there; } || echo bye
# Multi line (no else, single statement)
# Note: The exit status may not be the same as with an if statement
[[ "$var" == hello ]] && \
echo hi
# Multi line (no else)
[[ "$var" == hello ]] && {
echo hi
# ...
}
```
## Simpler `case` statement to set variable
The `:` built-in can be used to avoid repeating `variable=` in a case statement. The `$_` variable stores the last argument of the last command. `:` always succeeds so it can be used to store the variable value.
```shell
# Modified snippet from Neofetch.
case "$OSTYPE" in
"darwin"*)
: "MacOS"
;;
"linux"*)
: "Linux"
;;
*"bsd"* | "dragonfly" | "bitrig")
: "BSD"
;;
"cygwin" | "msys" | "win32")
: "Windows"
;;
*)
printf '%02x' "$B"
printf '%s\n' "Unknown OS detected, aborting..." >&2
exit 1
;;
esac
done
printf '\n'
}
```
**Example Usage:**
```shell
$ uuid
d5b6c731-1310-4c24-9fe3-55d556d44374
```
## Progress bars
This is a simple way of drawing progress bars without needing a for loop
in the function itself.
**Example Function:**
```sh
bar() {
# Usage: bar 1 10
# ^----- Elapsed Percentage (0-100).
# ^-- Total length in chars.
((elapsed=$1*$2/100))
# Create the bar with spaces.
printf -v prog "%${elapsed}s"
printf -v total "%$(($2-elapsed))s"
printf '%s\r' "[${prog// /-}${total}]"
}
```
**Example Usage:**
```shell
for ((i=0;i<=100;i++)); do
# Pure bash micro sleeps (for the example).
(:;:) && (:;:) && (:;:) && (:;:) && (:;:)
# Print the bar.
bar "$i" "10"
done
printf '\n'
```
## Get the list of functions in a script
```sh
get_functions() {
# Usage: get_functions
IFS=$'\n' read -d "" -ra functions < <(declare -F)
printf '%s\n' "${functions[@]//declare -f }"
}
```
## Bypass shell aliases
```shell
# alias
ls
# command
# shellcheck disable=SC1001
\ls
```
## Bypass shell functions
```shell
# function
ls
# command
command ls
# Finally, set the variable.
os="$_"
```
<!-- CHAPTER END -->

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# OTHER
## Use `read` as an alternative to the `sleep` command
Surprisingly, `sleep` is an external command and not a `bash` built-in.
**CAVEAT:** Requires `bash` 4+
**Example Function:**
```sh
read_sleep() {
# Usage: sleep 1
# sleep 0.2
read -rst "${1:-1}" -N 999
}
```
**Example Usage:**
```shell
read_sleep 1
read_sleep 0.1
read_sleep 30
```
## Check if a program is in the user's PATH
```shell
# There are 3 ways to do this and either one can be used.
type -p executable_name &>/dev/null
hash executable_name &>/dev/null
command -v executable_name &>/dev/null
# As a test.
if type -p executable_name &>/dev/null; then
# Program is in PATH.
fi
# Inverse.
if ! type -p executable_name &>/dev/null; then
# Program is not in PATH.
fi
# Example (Exit early if program is not installed).
if ! type -p convert &>/dev/null; then
printf '%s\n' "error: convert is not installed, exiting..."
exit 1
fi
```
## Get the current date using `strftime`
Bash’s `printf` has a built-in method of getting the date which can be used in place of the `date` command.
**CAVEAT:** Requires `bash` 4+
**Example Function:**
```sh
date() {
# Usage: date "format"
# See: 'man strftime' for format.
printf "%($1)T\\n" "-1"
}
```
**Example Usage:**
```shell
# Using above function.
$ date "%a %d %b - %l:%M %p"
Fri 15 Jun - 10:00 AM
# Using printf directly.
$ printf '%(%a %d %b - %l:%M %p)T\n' "-1"
Fri 15 Jun - 10:00 AM
# Assigning a variable using printf.
$ printf -v date '%(%a %d %b - %l:%M %p)T\n' '-1'
$ printf '%s\n' "$date"
Fri 15 Jun - 10:00 AM
```
## Generate a UUID V4
**Example Function:**
```sh
uuid() {
# Usage: uuid
C="89ab"
for ((N=0;N<16;++N)); do
B="$((RANDOM%256))"
case "$N" in
6) printf '4%x' "$((B%16))" ;;
8) printf '%c%x' "${C:$RANDOM%${#C}:1}" "$((B%16))" ;;
3|5|7|9)
printf '%02x-' "$B"
;;
*)
printf '%02x' "$B"
;;
esac
done
printf '\n'
}
```
**Example Usage:**
```shell
$ uuid
d5b6c731-1310-4c24-9fe3-55d556d44374
```
## Progress bars
This is a simple way of drawing progress bars without needing a for loop
in the function itself.
**Example Function:**
```sh
bar() {
# Usage: bar 1 10
# ^----- Elapsed Percentage (0-100).
# ^-- Total length in chars.
((elapsed=$1*$2/100))
# Create the bar with spaces.
printf -v prog "%${elapsed}s"
printf -v total "%$(($2-elapsed))s"
printf '%s\r' "[${prog// /-}${total}]"
}
```
**Example Usage:**
```shell
for ((i=0;i<=100;i++)); do
# Pure bash micro sleeps (for the example).
(:;:) && (:;:) && (:;:) && (:;:) && (:;:)
# Print the bar.
bar "$i" "10"
done
printf '\n'
```
## Get the list of functions in a script
```sh
get_functions() {
# Usage: get_functions
IFS=$'\n' read -d "" -ra functions < <(declare -F)
printf '%s\n' "${functions[@]//declare -f }"
}
```
## Bypass shell aliases
```shell
# alias
ls
# command
# shellcheck disable=SC1001
\ls
```
## Bypass shell functions
```shell
# function
ls
# command
command ls
```
<!-- CHAPTER END -->