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MIT License 28.8k stars 2.6k forks Star Notifications * Code * Issues 32 * Pull requests 15 * Actions * Security * Insights More * Code * Issues * Pull requests * Actions * Security * Insights This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository. master Switch branches/tags [ ] Branches Tags Could not load branches Nothing to show {{ refName }} default View all branches Could not load tags Nothing to show {{ refName }} default View all tags 1 branch 0 tags Code Latest commit @dylanaraps dylanaraps Merge pull request #106 from pipefail/master ... 8c19d0b Oct 21, 2020 Merge pull request #106 from pipefail/master add namerefs to avoid command substitution subproc for function output assignment 8c19d0b Git stats * 263 commits Files Permalink Failed to load latest commit information. Type Name Latest commit message Commit time manuscript add alternative to command substitution for func return Oct 20, 2020 .travis.yml run shellcheck in the test script Jun 15, 2018 CONTRIBUTING.md Update CONTRIBUTING.md Sep 23, 2020 LICENSE.md Added license Jun 14, 2018 README.md add alternative to command substitution for func return Oct 20, 2020 build.sh Added build files to turn the bible into a book Jun 20, 2018 test.sh docs: update Sep 19, 2019 View code [ ] pure bash bible Table of Contents FOREWORD STRINGS Trim leading and trailing white-space from string Trim all white-space from string and truncate spaces Use regex on a string Split a string on a delimiter Change a string to lowercase Change a string to uppercase Reverse a string case Trim quotes from a string Strip all instances of pattern from string Strip first occurrence of pattern from string Strip pattern from start of string Strip pattern from end of string Percent-encode a string Decode a percent-encoded string Check if string contains a sub-string Check if string starts with sub-string Check if string ends with sub-string ARRAYS Reverse an array Remove duplicate array elements Random array element Cycle through an array Toggle between two values LOOPS Loop over a range of numbers Loop over a variable range of numbers Loop over an array Loop over an array with an index Loop over the contents of a file Loop over files and directories FILE HANDLING Read a file to a string Read a file to an array (by line) Get the first N lines of a file Get the last N lines of a file Get the number of lines in a file Count files or directories in directory Create an empty file Extract lines between two markers FILE PATHS Get the directory name of a file path Get the base-name of a file path VARIABLES Assign and access a variable using a variable Name a variable based on another variable ESCAPE SEQUENCES Text Colors Text Attributes Cursor Movement Erasing Text PARAMETER EXPANSION Indirection Replacement Length Expansion Case Modification Default Value BRACE EXPANSION Ranges String Lists CONDITIONAL EXPRESSIONS File Conditionals File Comparisons Variable Conditionals Variable Comparisons ARITHMETIC OPERATORS Assignment Arithmetic Bitwise Logical Miscellaneous ARITHMETIC Simpler syntax to set variables Ternary Tests TRAPS Do something on script exit Ignore terminal interrupt (CTRL+C, SIGINT) React to window resize Do something before every command Do something when a shell function or a sourced file finishes executing PERFORMANCE Disable Unicode OBSOLETE SYNTAX Shebang Command Substitution Function Declaration INTERNAL VARIABLES Get the location to the bash binary Get the version of the current running bash process Open the user's preferred text editor Get the name of the current function Get the host-name of the system Get the architecture of the Operating System Get the name of the Operating System / Kernel Get the current working directory Get the number of seconds the script has been running Get a pseudorandom integer INFORMATION ABOUT THE TERMINAL Get the terminal size in lines and columns (from a script) Get the terminal size in pixels Get the current cursor position CONVERSION Convert a hex color to RGB Convert an RGB color to hex CODE GOLF Shorter for loop syntax Shorter infinite loops Shorter function declaration Shorter if syntax Simpler case statement to set variable OTHER Use read as an alternative to the sleep command Check if a program is in the user's PATH Get the current date using strftime Get the username of the current user Generate a UUID V4 Progress bars Get the list of functions in a script Bypass shell aliases Bypass shell functions Run a command in the background Capture the return value of a function without command substitution AFTERWORD README.md NEW: pure sh bible ( A collection of pure POSIX sh alternatives to external processes). [512x512] pure bash bible A collection of pure bash alternatives to external processes. [6874747073] [6874747073] [68747470733a2f2f73332e616d] The goal of this book is to document commonly-known and lesser-known methods of doing various tasks using only built-in bash features. Using the snippets from this bible can help remove unneeded dependencies from scripts and in most cases make them faster. I came across these tips and discovered a few while developing neofetch, pxltrm and other smaller projects. The snippets below are linted using shellcheck and tests have been written where applicable. Want to contribute? Read the CONTRIBUTING.md. It outlines how the unit tests work and what is required when adding snippets to the bible. See something incorrectly described, buggy or outright wrong? Open an issue or send a pull request. If the bible is missing something, open an issue and a solution will be found. This book is also available to purchase on leanpub. https:// leanpub.com/bash Or you can buy me a coffee. [6874747073] [6874747073] [6874747073] Table of Contents * FOREWORD * STRINGS + Trim leading and trailing white-space from string + Trim all white-space from string and truncate spaces + Use regex on a string + Split a string on a delimiter + Change a string to lowercase + Change a string to uppercase + Reverse a string case + Trim quotes from a string + Strip all instances of pattern from string + Strip first occurrence of pattern from string + Strip pattern from start of string + Strip pattern from end of string + Percent-encode a string + Decode a percent-encoded string + Check if string contains a sub-string + Check if string starts with sub-string + Check if string ends with sub-string * ARRAYS + Reverse an array + Remove duplicate array elements + Random array element + Cycle through an array + Toggle between two values * LOOPS + Loop over a range of numbers + Loop over a variable range of numbers + Loop over an array + Loop over an array with an index + Loop over the contents of a file + Loop over files and directories * FILE HANDLING + Read a file to a string + Read a file to an array (by line) + Get the first N lines of a file + Get the last N lines of a file + Get the number of lines in a file + Count files or directories in directory + Create an empty file + Extract lines between two markers * FILE PATHS + Get the directory name of a file path + Get the base-name of a file path * VARIABLES + Assign and access a variable using a variable + Name a variable based on another variable * ESCAPE SEQUENCES + Text Colors + Text Attributes + Cursor Movement + Erasing Text * PARAMETER EXPANSION + Indirection + Replacement + Length + Expansion + Case Modification + Default Value * BRACE EXPANSION + Ranges + String Lists * CONDITIONAL EXPRESSIONS + File Conditionals + File Comparisons + Variable Conditionals + Variable Comparisons * ARITHMETIC OPERATORS + Assignment + Arithmetic + Bitwise + Logical + Miscellaneous * ARITHMETIC + Simpler syntax to set variables + Ternary Tests * TRAPS + Do something on script exit + Ignore terminal interrupt (CTRL+C, SIGINT) + React to window resize + Do something before every command + Do something when a shell function or a sourced file finishes executing * PERFORMANCE + Disable Unicode * OBSOLETE SYNTAX + Shebang + Command Substitution + Function Declaration * INTERNAL VARIABLES + Get the location to the bash binary + Get the version of the current running bash process + Open the user's preferred text editor + Get the name of the current function + Get the host-name of the system + Get the architecture of the Operating System + Get the name of the Operating System / Kernel + Get the current working directory + Get the number of seconds the script has been running + Get a pseudorandom integer * INFORMATION ABOUT THE TERMINAL + Get the terminal size in lines and columns (from a script) + Get the terminal size in pixels + Get the current cursor position * CONVERSION + Convert a hex color to RGB + Convert an RGB color to hex * CODE GOLF + Shorter for loop syntax + Shorter infinite loops + Shorter function declaration + Shorter if syntax + Simpler case statement to set variable * OTHER + Use read as an alternative to the sleep command + Check if a program is in the user's PATH + Get the current date using strftime + Get the username of the current user + Generate a UUID V4 + Progress bars + Get the list of functions in a script + Bypass shell aliases + Bypass shell functions + Run a command in the background + Capture function return without command substitution * AFTERWORD FOREWORD A collection of pure bash alternatives to external processes and programs. The bash scripting language is more powerful than people realise and most tasks can be accomplished without depending on external programs. Calling an external process in bash is expensive and excessive use will cause a noticeable slowdown. Scripts and programs written using built-in methods (where applicable) will be faster, require fewer dependencies and afford a better understanding of the language itself. The contents of this book provide a reference for solving problems encountered when writing programs and scripts in bash. Examples are in function formats showcasing how to incorporate these solutions into code. STRINGS Trim leading and trailing white-space from string This is an alternative to sed, awk, perl and other tools. The function below works by finding all leading and trailing white-space and removing it from the start and end of the string. The : built-in is used in place of a temporary variable. Example Function: trim_string() { # Usage: trim_string " example string " : "${1#"${1%%[![:space:]]*}"}" : "${_%"${_##*[![:space:]]}"}" printf '%s\n' "$_" } Example Usage: $ trim_string " Hello, World " Hello, World $ name=" John Black " $ trim_string "$name" John Black Trim all white-space from string and truncate spaces This is an alternative to sed, awk, perl and other tools. The function below works by abusing word splitting to create a new string without leading/trailing white-space and with truncated spaces. Example Function: # shellcheck disable=SC2086,SC2048 trim_all() { # Usage: trim_all " example string " set -f set -- $* printf '%s\n' "$*" set +f } Example Usage: $ trim_all " Hello, World " Hello, World $ name=" John Black is my name. " $ trim_all "$name" John Black is my name. Use regex on a string The result of bash's regex matching can be used to replace sed for a large number of use-cases. CAVEAT: This is one of the few platform dependent bash features. bash will use whatever regex engine is installed on the user's system. Stick to POSIX regex features if aiming for compatibility. CAVEAT: This example only prints the first matching group. When using multiple capture groups some modification is needed. Example Function: regex() { # Usage: regex "string" "regex" [[ $1 =~ $2 ]] && printf '%s\n' "${BASH_REMATCH[1]}" } Example Usage: $ # Trim leading white-space. $ regex ' hello' '^\s*(.*)' hello $ # Validate a hex color. $ regex "#FFFFFF" '^(#?([a-fA-F0-9]{6}|[a-fA-F0-9]{3}))$' #FFFFFF $ # Validate a hex color (invalid). $ regex "red" '^(#?([a-fA-F0-9]{6}|[a-fA-F0-9]{3}))$' # no output (invalid) Example Usage in script: is_hex_color() { if [[ $1 =~ ^(#?([a-fA-F0-9]{6}|[a-fA-F0-9]{3}))$ ]]; then printf '%s\n' "${BASH_REMATCH[1]}" else printf '%s\n' "error: $1 is an invalid color." return 1 fi } read -r color is_hex_color "$color" || color="#FFFFFF" # Do stuff. Split a string on a delimiter CAVEAT: Requires bash 4+ This is an alternative to cut, awk and other tools. Example Function: split() { # Usage: split "string" "delimiter" IFS=$'\n' read -d "" -ra arr <<< "${1//$2/$'\n'}" printf '%s\n' "${arr[@]}" } Example Usage: $ split "apples,oranges,pears,grapes" "," apples oranges pears grapes $ split "1, 2, 3, 4, 5" ", " 1 2 3 4 5 # Multi char delimiters work too! $ split "hello---world---my---name---is---john" "---" hello world my name is john Change a string to lowercase CAVEAT: Requires bash 4+ Example Function: lower() { # Usage: lower "string" printf '%s\n' "${1,,}" } Example Usage: $ lower "HELLO" hello $ lower "HeLlO" hello $ lower "hello" hello Change a string to uppercase CAVEAT: Requires bash 4+ Example Function: upper() { # Usage: upper "string" printf '%s\n' "${1^^}" } Example Usage: $ upper "hello" HELLO $ upper "HeLlO" HELLO $ upper "HELLO" HELLO Reverse a string case CAVEAT: Requires bash 4+ Example Function: reverse_case() { # Usage: reverse_case "string" printf '%s\n' "${1~~}" } Example Usage: $ reverse_case "hello" HELLO $ reverse_case "HeLlO" hElLo $ reverse_case "HELLO" hello Trim quotes from a string Example Function: trim_quotes() { # Usage: trim_quotes "string" : "${1//\'}" printf '%s\n' "${_//\"}" } Example Usage: $ var="'Hello', \"World\"" $ trim_quotes "$var" Hello, World Strip all instances of pattern from string Example Function: strip_all() { # Usage: strip_all "string" "pattern" printf '%s\n' "${1//$2}" } Example Usage: $ strip_all "The Quick Brown Fox" "[aeiou]" Th Qck Brwn Fx $ strip_all "The Quick Brown Fox" "[[:space:]]" TheQuickBrownFox $ strip_all "The Quick Brown Fox" "Quick " The Brown Fox Strip first occurrence of pattern from string Example Function: strip() { # Usage: strip "string" "pattern" printf '%s\n' "${1/$2}" } Example Usage: $ strip "The Quick Brown Fox" "[aeiou]" Th Quick Brown Fox $ strip "The Quick Brown Fox" "[[:space:]]" TheQuick Brown Fox Strip pattern from start of string Example Function: lstrip() { # Usage: lstrip "string" "pattern" printf '%s\n' "${1##$2}" } Example Usage: $ lstrip "The Quick Brown Fox" "The " Quick Brown Fox Strip pattern from end of string Example Function: rstrip() { # Usage: rstrip "string" "pattern" printf '%s\n' "${1%%$2}" } Example Usage: $ rstrip "The Quick Brown Fox" " Fox" The Quick Brown Percent-encode a string Example Function: urlencode() { # Usage: urlencode "string" local LC_ALL=C for (( i = 0; i < ${#1}; i++ )); do : "${1:i:1}" case "$_" in [a-zA-Z0-9.~_-]) printf '%s' "$_" ;; *) printf '%%%02X' "'$_" ;; esac done printf '\n' } Example Usage: $ urlencode "https://github.com/dylanaraps/pure-bash-bible" https%3A%2F%2Fgithub.com%2Fdylanaraps%2Fpure-bash-bible Decode a percent-encoded string Example Function: urldecode() { # Usage: urldecode "string" : "${1//+/ }" printf '%b\n' "${_//%/\\x}" } Example Usage: $ urldecode "https%3A%2F%2Fgithub.com%2Fdylanaraps%2Fpure-bash-bible" https://github.com/dylanaraps/pure-bash-bible Check if string contains a sub-string Using a test: if [[ $var == *sub_string* ]]; then printf '%s\n' "sub_string is in var." fi # Inverse (substring not in string). if [[ $var != *sub_string* ]]; then printf '%s\n' "sub_string is not in var." fi # This works for arrays too! if [[ ${arr[*]} == *sub_string* ]]; then printf '%s\n' "sub_string is in array." fi Using a case statement: case "$var" in *sub_string*) # Do stuff ;; *sub_string2*) # Do more stuff ;; *) # Else ;; esac Check if string starts with sub-string if [[ $var == sub_string* ]]; then printf '%s\n' "var starts with sub_string." fi # Inverse (var does not start with sub_string). if [[ $var != sub_string* ]]; then printf '%s\n' "var does not start with sub_string." fi Check if string ends with sub-string if [[ $var == *sub_string ]]; then printf '%s\n' "var ends with sub_string." fi # Inverse (var does not end with sub_string). if [[ $var != *sub_string ]]; then printf '%s\n' "var does not end with sub_string." fi ARRAYS Reverse an array Enabling extdebug allows access to the BASH_ARGV array which stores the current function's arguments in reverse. CAVEAT: Requires shopt -s compat44 in bash 5.0+. Example Function: reverse_array() { # Usage: reverse_array "array" shopt -s extdebug f()(printf '%s\n' "${BASH_ARGV[@]}"); f "$@" shopt -u extdebug } Example Usage: $ reverse_array 1 2 3 4 5 5 4 3 2 1 $ arr=(red blue green) $ reverse_array "${arr[@]}" green blue red Remove duplicate array elements Create a temporary associative array. When setting associative array values and a duplicate assignment occurs, bash overwrites the key. This allows us to effectively remove array duplicates. CAVEAT: Requires bash 4+ CAVEAT: List order may not stay the same. Example Function: remove_array_dups() { # Usage: remove_array_dups "array" declare -A tmp_array for i in "$@"; do [[ $i ]] && IFS=" " tmp_array["${i:- }"]=1 done printf '%s\n' "${!tmp_array[@]}" } Example Usage: $ remove_array_dups 1 1 2 2 3 3 3 3 3 4 4 4 4 4 5 5 5 5 5 5 1 2 3 4 5 $ arr=(red red green blue blue) $ remove_array_dups "${arr[@]}" red green blue Random array element Example Function: random_array_element() { # Usage: random_array_element "array" local arr=("$@") printf '%s\n' "${arr[RANDOM % $#]}" } Example Usage: $ array=(red green blue yellow brown) $ random_array_element "${array[@]}" yellow # Multiple arguments can also be passed. $ random_array_element 1 2 3 4 5 6 7 3 Cycle through an array Each time the printf is called, the next array element is printed. When the print hits the last array element it starts from the first element again. arr=(a b c d) cycle() { printf '%s ' "${arr[${i:=0}]}" ((i=i>=${#arr[@]}-1?0:++i)) } Toggle between two values This works the same as above, this is just a different use case. arr=(true false) cycle() { printf '%s ' "${arr[${i:=0}]}" ((i=i>=${#arr[@]}-1?0:++i)) } LOOPS Loop over a range of numbers Alternative to seq. # Loop from 0-100 (no variable support). for i in {0..100}; do printf '%s\n' "$i" done Loop over a variable range of numbers Alternative to seq. # Loop from 0-VAR. VAR=50 for ((i=0;i<=VAR;i++)); do printf '%s\n' "$i" done Loop over an array arr=(apples oranges tomatoes) # Just elements. for element in "${arr[@]}"; do printf '%s\n' "$element" done Loop over an array with an index arr=(apples oranges tomatoes) # Elements and index. for i in "${!arr[@]}"; do printf '%s\n' "${arr[i]}" done # Alternative method. for ((i=0;i<${#arr[@]};i++)); do printf '%s\n' "${arr[i]}" done Loop over the contents of a file while read -r line; do printf '%s\n' "$line" done < "file" Loop over files and directories Don't use ls. # Greedy example. for file in *; do printf '%s\n' "$file" done # PNG files in dir. for file in ~/Pictures/*.png; do printf '%s\n' "$file" done # Iterate over directories. for dir in ~/Downloads/*/; do printf '%s\n' "$dir" done # Brace Expansion. for file in /path/to/parentdir/{file1,file2,subdir/file3}; do printf '%s\n' "$file" done # Iterate recursively. shopt -s globstar for file in ~/Pictures/**/*; do printf '%s\n' "$file" done shopt -u globstar FILE HANDLING CAVEAT: bash does not handle binary data properly in versions < 4.4. Read a file to a string Alternative to the cat command. file_data="$(<"file")" Read a file to an array (by line) Alternative to the cat command. # Bash <4 (discarding empty lines). IFS=$'\n' read -d "" -ra file_data < "file" # Bash <4 (preserving empty lines). while read -r line; do file_data+=("$line") done < "file" # Bash 4+ mapfile -t file_data < "file" Get the first N lines of a file Alternative to the head command. CAVEAT: Requires bash 4+ Example Function: head() { # Usage: head "n" "file" mapfile -tn "$1" line < "$2" printf '%s\n' "${line[@]}" } Example Usage: $ head 2 ~/.bashrc # Prompt PS1=' ' $ head 1 ~/.bashrc # Prompt Get the last N lines of a file Alternative to the tail command. CAVEAT: Requires bash 4+ Example Function: tail() { # Usage: tail "n" "file" mapfile -tn 0 line < "$2" printf '%s\n' "${line[@]: -$1}" } Example Usage: $ tail 2 ~/.bashrc # Enable tmux. # [[ -z "$TMUX" ]] && exec tmux $ tail 1 ~/.bashrc # [[ -z "$TMUX" ]] && exec tmux Get the number of lines in a file Alternative to wc -l. Example Function (bash 4): lines() { # Usage: lines "file" mapfile -tn 0 lines < "$1" printf '%s\n' "${#lines[@]}" } Example Function (bash 3): This method uses less memory than the mapfile method and works in bash 3 but it is slower for bigger files. lines_loop() { # Usage: lines_loop "file" count=0 while IFS= read -r _; do ((count++)) done < "$1" printf '%s\n' "$count" } Example Usage: $ lines ~/.bashrc 48 $ lines_loop ~/.bashrc 48 Count files or directories in directory This works by passing the output of the glob to the function and then counting the number of arguments. Example Function: count() { # Usage: count /path/to/dir/* # count /path/to/dir/*/ printf '%s\n' "$#" } Example Usage: # Count all files in dir. $ count ~/Downloads/* 232 # Count all dirs in dir. $ count ~/Downloads/*/ 45 # Count all jpg files in dir. $ count ~/Pictures/*.jpg 64 Create an empty file Alternative to touch. # Shortest. >file # Longer alternatives: :>file echo -n >file printf '' >file Extract lines between two markers Example Function: extract() { # Usage: extract file "opening marker" "closing marker" while IFS=$'\n' read -r line; do [[ $extract && $line != "$3" ]] && printf '%s\n' "$line" [[ $line == "$2" ]] && extract=1 [[ $line == "$3" ]] && extract= done < "$1" } Example Usage: # Extract code blocks from MarkDown file. $ extract ~/projects/pure-bash/README.md '```sh' '```' # Output here... FILE PATHS Get the directory name of a file path Alternative to the dirname command. Example Function: dirname() { # Usage: dirname "path" local tmp=${1:-.} [[ $tmp != *[!/]* ]] && { printf '/\n' return } tmp=${tmp%%"${tmp##*[!/]}"} [[ $tmp != */* ]] && { printf '.\n' return } tmp=${tmp%/*} tmp=${tmp%%"${tmp##*[!/]}"} printf '%s\n' "${tmp:-/}" } Example Usage: $ dirname ~/Pictures/Wallpapers/1.jpg /home/black/Pictures/Wallpapers $ dirname ~/Pictures/Downloads/ /home/black/Pictures Get the base-name of a file path Alternative to the basename command. Example Function: basename() { # Usage: basename "path" ["suffix"] local tmp tmp=${1%"${1##*[!/]}"} tmp=${tmp##*/} tmp=${tmp%"${2/"$tmp"}"} printf '%s\n' "${tmp:-/}" } Example Usage: $ basename ~/Pictures/Wallpapers/1.jpg 1.jpg $ basename ~/Pictures/Wallpapers/1.jpg .jpg 1 $ basename ~/Pictures/Downloads/ Downloads VARIABLES Assign and access a variable using a variable $ hello_world="value" # Create the variable name. $ var="world" $ ref="hello_$var" # Print the value of the variable name stored in 'hello_$var'. $ printf '%s\n' "${!ref}" value Alternatively, on bash 4.3+: $ hello_world="value" $ var="world" # Declare a nameref. $ declare -n ref=hello_$var $ printf '%s\n' "$ref" value Name a variable based on another variable $ var="world" $ declare "hello_$var=value" $ printf '%s\n' "$hello_world" value ESCAPE SEQUENCES Contrary to popular belief, there is no issue in utilizing raw escape sequences. Using tput abstracts the same ANSI sequences as if printed manually. Worse still, tput is not actually portable. There are a number of tput variants each with different commands and syntaxes ( try tput setaf 3 on a FreeBSD system). Raw sequences are fine. Text Colors NOTE: Sequences requiring RGB values only work in True-Color Terminal Emulators. Sequence What does it do? Value \e[38;5;m Set text foreground color. 0-255 \e[48;5;m Set text background color. 0-255 \e[38;2;;;m Set text foreground color to RGB color. R, G, B \e[48;2;;;m Set text background color to RGB color. R, G, B Text Attributes NOTE: Prepend 2 to any code below to turn it's effect off (examples: 21=bold text off, 22=faint text off, 23=italic text off). Sequence What does it do? \e[m Reset text formatting and colors. \e[1m Bold text. \e[2m Faint text. \e[3m Italic text. \e[4m Underline text. \e[5m Blinking text. \e[7m Highlighted text. \e[8m Hidden text. \e[9m Strike-through text. Cursor Movement Sequence What does it do? Value \e[;H Move cursor to absolute position. line, column \e[H Move cursor to home position (0,0). \e[A Move cursor up N lines. num \e[B Move cursor down N lines. num \e[C Move cursor right N columns. num \e[D Move cursor left N columns. num \e[s Save cursor position. \e[u Restore cursor position. Erasing Text Sequence What does it do? \e[K Erase from cursor position to end of line. \e[1K Erase from cursor position to start of line. \e[2K Erase the entire current line. \e[J Erase from the current line to the bottom of the screen. \e[1J Erase from the current line to the top of the screen. \e[2J Clear the screen. \e[2J\e[H Clear the screen and move cursor to 0,0. PARAMETER EXPANSION Indirection Parameter What does it do? ${!VAR} Access a variable based on the value of VAR. ${!VAR*} Expand to IFS separated list of variable names starting with VAR. Expand to IFS separated list of variable names starting ${!VAR@} with VAR. If double-quoted, each variable name expands to a separate word. Replacement Parameter What does it do? ${VAR#PATTERN} Remove shortest match of pattern from start of string. ${VAR##PATTERN} Remove longest match of pattern from start of string. ${VAR%PATTERN} Remove shortest match of pattern from end of string. ${VAR%%PATTERN} Remove longest match of pattern from end of string. ${VAR/PATTERN/ Replace first match with string. REPLACE} ${VAR//PATTERN/ Replace all matches with string. REPLACE} ${VAR/PATTERN} Remove first match. ${VAR//PATTERN} Remove all matches. Length Parameter What does it do? ${#VAR} Length of var in characters. ${#ARR[@]} Length of array in elements. Expansion Parameter What does it do? ${VAR:OFFSET} Remove first N chars from variable. Get substring from N character to N character. ${VAR:OFFSET:LENGTH} (${VAR:10:10}: Get sub-string from char 10 to char 20) ${VAR:: OFFSET} Get first N chars from variable. ${VAR:: -OFFSET} Remove last N chars from variable. ${VAR: -OFFSET} Get last N chars from variable. $ Cut first N chars and last N chars. {VAR:OFFSET:-OFFSET} Case Modification Parameter What does it do? CAVEAT ${VAR^} Uppercase first character. bash 4+ ${VAR^^} Uppercase all characters. bash 4+ ${VAR,} Lowercase first character. bash 4+ ${VAR,,} Lowercase all characters. bash 4+ ${VAR~} Reverse case of first character. bash 4+ ${VAR~~} Reverse case of all characters. bash 4+ Default Value Parameter What does it do? $ If VAR is empty or unset, use STRING as its value. {VAR:-STRING} ${VAR-STRING} If VAR is unset, use STRING as its value. ${VAR:= If VAR is empty or unset, set the value of VAR to STRING} STRING. ${VAR=STRING} If VAR is unset, set the value of VAR to STRING. $ If VAR is not empty, use STRING as its value. {VAR:+STRING} ${VAR+STRING} If VAR is set, use STRING as its value. ${VAR:? Display an error if empty or unset. STRING} ${VAR?STRING} Display an error if unset. BRACE EXPANSION Ranges # Syntax: {..} # Print numbers 1-100. echo {1..100} # Print range of floats. echo 1.{1..9} # Print chars a-z. echo {a..z} echo {A..Z} # Nesting. echo {A..Z}{0..9} # Print zero-padded numbers. # CAVEAT: bash 4+ echo {01..100} # Change increment amount. # Syntax: {....} # CAVEAT: bash 4+ echo {1..10..2} # Increment by 2. String Lists echo {apples,oranges,pears,grapes} # Example Usage: # Remove dirs Movies, Music and ISOS from ~/Downloads/. rm -rf ~/Downloads/{Movies,Music,ISOS} CONDITIONAL EXPRESSIONS File Conditionals Expression Value What does it do? -a file If file exists. -b file If file exists and is a block special file. -c file If file exists and is a character special file. -d file If file exists and is a directory. -e file If file exists. -f file If file exists and is a regular file. -g file If file exists and its set-group-id bit is set. -h file If file exists and is a symbolic link. -k file If file exists and its sticky-bit is set -p file If file exists and is a named pipe (FIFO). -r file If file exists and is readable. -s file If file exists and its size is greater than zero. -t fd If file descriptor is open and refers to a terminal. -u file If file exists and its set-user-id bit is set. -w file If file exists and is writable. -x file If file exists and is executable. -G file If file exists and is owned by the effective group ID. -L file If file exists and is a symbolic link. -N file If file exists and has been modified since last read. -O file If file exists and is owned by the effective user ID. -S file If file exists and is a socket. File Comparisons Expression What does it do? file -ef If both files refer to the same inode and device numbers. file2 file -nt If file is newer than file2 (uses modification time) or file2 file exists and file2 does not. file -ot If file is older than file2 (uses modification time) or file2 file2 exists and file does not. Variable Conditionals Expression Value What does it do? -o opt If shell option is enabled. -v var If variable has a value assigned. -R var If variable is a name reference. -z var If the length of string is zero. -n var If the length of string is non-zero. Variable Comparisons Expression What does it do? var = var2 Equal to. var == var2 Equal to (synonym for =). var != var2 Not equal to. var < var2 Less than (in ASCII alphabetical order.) var > var2 Greater than (in ASCII alphabetical order.) 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)) ARITHMETIC Simpler syntax to set variables # Simple math ((var=1+2)) # Decrement/Increment variable ((var++)) ((var--)) ((var+=1)) ((var-=1)) # Using variables ((var=var2*arr[2])) Ternary Tests # 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)) TRAPS Traps allow a script to execute code on various signals. In 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 # Clear screen on script exit. trap 'printf \\e[2J\\e[H\\e[m' EXIT Ignore terminal interrupt (CTRL+C, SIGINT) trap '' INT React to window resize # Call a function on window resize. trap 'code_here' SIGWINCH Do something before every command trap 'code_here' DEBUG Do something when a shell function or a sourced file finishes executing trap 'code_here' RETURN PERFORMANCE Disable Unicode If unicode is not required, it can be disabled for a performance increase. Results may vary however there have been noticeable improvements in neofetch and other programs. # Disable unicode. LC_ALL=C LANG=C OBSOLETE SYNTAX 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. NOTE: There are times when one may have a good reason for using #!/ bin/bash or another direct path to the binary. # Right: #!/usr/bin/env bash # Less right: #!/bin/bash Command Substitution Use $() instead of ` `. # Right. var="$(command)" # Wrong. var=`command` # $() can easily be nested whereas `` cannot. var="$(command "$(command)")" Function Declaration Do not use the function keyword, it reduces compatibility with older versions of bash. # Right. do_something() { # ... } # Wrong. function do_something() { # ... } INTERNAL VARIABLES Get the location to the bash binary "$BASH" Get the version of the current running bash process # As a string. "$BASH_VERSION" # As an array. "${BASH_VERSINFO[@]}" Open the user's preferred text editor "$EDITOR" "$file" # NOTE: This variable may be empty, set a fallback value. "${EDITOR:-vi}" "$file" Get the name of the current function # Current function. "${FUNCNAME[0]}" # Parent function. "${FUNCNAME[1]}" # So on and so forth. "${FUNCNAME[2]}" "${FUNCNAME[3]}" # All functions including parents. "${FUNCNAME[@]}" Get the host-name of the system "$HOSTNAME" # NOTE: This variable may be empty. # Optionally set a fallback to the hostname command. "${HOSTNAME:-$(hostname)}" Get the architecture of the Operating System "$HOSTTYPE" Get the name of the Operating System / Kernel This can be used to add conditional support for different Operating Systems without needing to call uname. "$OSTYPE" Get the current working directory This is an alternative to the pwd built-in. "$PWD" Get the number of seconds the script has been running "$SECONDS" Get a pseudorandom integer Each time $RANDOM is used, a different integer between 0 and 32767 is returned. This variable should not be used for anything related to security (this includes encryption keys etc). "$RANDOM" INFORMATION ABOUT THE TERMINAL 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: 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: # Output: LINES COLUMNS $ get_term_size 15 55 Get the terminal size in pixels CAVEAT: This does not work in some terminal emulators. Example Function: 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: # Output: WIDTHxHEIGHT $ get_window_size 1200x800 # Output (fail): $ get_window_size x Get the current cursor position This is useful when creating a TUI in pure bash. Example Function: get_cursor_pos() { # Usage: get_cursor_pos IFS='[;' read -p $'\e[6n' -d R -rs _ y x _ printf '%s\n' "$x $y" } Example Usage: # Output: X Y $ get_cursor_pos 1 8 CONVERSION Convert a hex color to RGB Example Function: hex_to_rgb() { # Usage: hex_to_rgb "#FFFFFF" # hex_to_rgb "000000" : "${1/\#}" ((r=16#${_:0:2},g=16#${_:2:2},b=16#${_:4:2})) printf '%s\n' "$r $g $b" } Example Usage: $ hex_to_rgb "#FFFFFF" 255 255 255 Convert an RGB color to hex Example Function: rgb_to_hex() { # Usage: rgb_to_hex "r" "g" "b" printf '#%02x%02x%02x\n' "$1" "$2" "$3" } Example Usage: $ rgb_to_hex "255" "255" "255" #FFFFFF CODE GOLF Shorter for loop syntax # 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 # Normal method while :; do echo hi; done # Shorter for((;;)){ echo hi;} Shorter function declaration # 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 # 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 $_ variable stores the last argument of the last command. : always succeeds so it can be used to store the variable value. # Modified snippet from Neofetch. case "$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="$_" 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: read_sleep() { # Usage: read_sleep 1 # read_sleep 0.2 read -rt "$1" <> <(:) || : } Example Usage: read_sleep 1 read_sleep 0.1 read_sleep 30 For performance-critical situations, where it is not economic to open and close an excessive number of file descriptors, the allocation of a file descriptor may be done only once for all invocations of read: (See the generic original implementation at https://blog.dhampir.no/ content/ sleeping-without-a-subprocess-in-bash-and-how-to-sleep-forever) exec {sleep_fd}<> <(:) while some_quick_test; do # equivalent of sleep 0.001 read -t 0.001 -u $sleep_fd done Check if a program is in the user's PATH # 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: date() { # Usage: date "format" # See: 'man strftime' for format. printf "%($1)T\\n" "-1" } Example Usage: # 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 Get the username of the current user CAVEAT: Requires bash 4.4+ $ : \\u # Expand the parameter as if it were a prompt string. $ printf '%s\n' "${_@P}" black Generate a UUID V4 CAVEAT: The generated value is not cryptographically secure. Example Function: uuid() { # Usage: uuid C="89ab" for ((N=0;N<16;++N)); do B="$((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: $ 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: 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// /-}${total}]" } Example Usage: for ((i=0;i<=100;i++)); do # Pure bash micro sleeps (for the example). (:;:) && (:;:) && (:;:) && (:;:) && (:;:) # Print the bar. bar "$i" "10" done printf '\n' Get the list of functions in a script get_functions() { # Usage: get_functions IFS=$'\n' read -d "" -ra functions < <(declare -F) printf '%s\n' "${functions[@]//declare -f }" } Bypass shell aliases # alias ls # command # shellcheck disable=SC1001 \ls Bypass shell functions # function ls # command command ls Run a command in the background This will run the given command and keep it running, even after the terminal or SSH connection is terminated. All output is ignored. bkr() { (nohup "$@" &>/dev/null &) } bkr ./some_script.sh # some_script.sh is now running in the background Capture the return value of a function without command substitution CAVEAT: Requires bash 4+ This uses local namerefs to avoid using var=$(some_func) style command substitution for function output capture. to_upper() { local -n ptr=${1} ptr=${ptr^^} } foo="bar" to_upper foo printf "%s\n" "${foo}" # BAR AFTERWORD Thanks for reading! If this bible helped you in any way and you'd like to give back, consider donating. Donations give me the time to make this the best resource possible. Can't donate? That's OK, star the repo and share it with your friends! [6874747073] Rock on. About A collection of pure bash alternatives to external processes. Topics shell bash learning list script book reference guide handbook bible how-to shell-scripts Resources Readme License MIT License Stars 28.8k stars Watchers 714 watching Forks 2.6k forks Releases No releases published Packages 0 No packages published Contributors 21 * @dylanaraps * @paxperscientiam * @Crestwave * @sal666 * @CoolOppo * @Cuttlerat * @rahuldaniel * @sumbach * @pipefail * @frnchr * @amiryal + 10 contributors Languages * Shell 100.0% * (c) 2022 GitHub, Inc. * Terms * Privacy * Security * Status * Docs * Contact GitHub * Pricing * API * Training * Blog * About You can't perform that action at this time. You signed in with another tab or window. Reload to refresh your session. You signed out in another tab or window. Reload to refresh your session.