Bash Cheat Sheet

#!/bin/bash

echo "Hello World"

bash ./hello-world.sh

#!/bin/bash

# Assign a value to a variable
name="John Doe"

# Print the variable
echo $name

#!/bin/bash

# This is an inline comment

: '
This is an
multi-line comment
'

#!/bin/bash

# Print the first argument
echo $1

# Print all the arguments
echo $*

# Print all the arguments starting from the first one
echo $@

bash ./arguments.sh "Hello" "World"

#!/bin/bash

# Define a function
function World() {
  echo "World"
}

# Call the function
echo "Hello $(World)"

#!/bin/bash

# Define a variable
name="John Doe"

# Check if the variable is empty
if [ -z "$name" ]; then
  echo "The variable is empty"
else
  echo "The variable is not empty"
fi

#!/bin/bash

# Create a directory a, b, c
mkdir {a,b,c}

# Create a file with the name a.ts, b.ts, c.ts
touch {a,b,c}.ts

# Create a file with the name 1.txt, 2.txt, 3.txt, 4.txt, 5.txt
touch {1..5}.txt

#!/bin/bash

# Execute a command
echo "Hello $(whoami)"

# Execute a command with ``
echo "Hello `whoami`"

# !/bin/bash

echo ${FOO:-val} # Use the value of $FOO if it is set, otherwise use val.

STR="/path/to/file.txt"

# Remove the extension
echo ${STR%.txt} # /path/to/file

# Change the extension
echo ${STR%.txt}.md # /path/to/file.md

# Get the directory
echo ${STR%/*} # /path/to

# Get the extension
echo ${STR##*.} # txt

# Get the file
echo ${STR##*/} # file.txt

# Change the file name to test
echo ${STR/file/test} # /path/to/test.txt

#!/bin/bash

STR="Hello World"

# Get the first 5 characters
echo ${STR:0:5} # Hello

# Get the last 5 characters
echo ${STR:(-5):5} # World

#!/bin/bash

STR="/path/to/file.txt"

# Get the basepath
echo ${STR##*/} # file.txt

# Get the dirpath
echo ${STR%/*} # /path/to

#!/bin/bash

STR="Hello World"

# Convert to uppercase
echo ${STR^^} # HELLO WORLD

# Convert to lowercase
echo ${STR,,} # hello world

# Capitalize the first letter
echo ${STR^} # Hello world

# Capitalize the first letter of each word
echo ${STR^^^} # Hello World

# Capitalize the first letter of each word
echo ${STR^ ^} # Hello World

# Capitalize the first letter of each word
echo "${STR[@]^}" # Hello World

# lowercase the first letter of each word
echo "${STR[@],}" # hello world

#!/bin/bash

# Define an array
NUMBERS=(1 2 3)

# Define an array with a range
array[0]=1
array[1]=2
array[2]=3

# Define an array with a range
array=({1..3})

# Define an array1, array2, and array3
array1=(1 2 3)
array2=(4 5 6)
array3=(7 8 9)

# Merge the arrays
array=("${array1[@]}" "${array2[@]}" "${array3[@]}")

# Declare an array with a range
declare -a numbers(1 2 3)

# Add an element to the array in the last position
numbers+=4

# Add an element to the array in the first position
numbers=(0 "${numbers[@]}")

# Add an element to the array in the second position
numbers=("${numbers[@]:0:1}" "1" "${numbers[@]:1}")

#!/bin/bash

# Define an array
NUMBERS=(1 2 3)

# Iterate over the array
for i in "${NUMBERS[@]}"; do
  echo $i
done

# Iterate over the array with index

for i in "${!NUMBERS[@]}"; do
  echo "$i: ${NUMBERS[$i]}"
done

#!/bin/bash

# Define an array
NAMES=("John" "Jane" "Jack")

# Push an element to the array
NAMES=("${NAMES[@]}" "Jill")

# Other way to push an element to the array
NAMES+=("Jill")

# Remove by RegEx pattern matching
NAMES=("${NAMES[@]/*ll*/}")

# Remove one element by index
unset NAMES[0]

# Duplicate an array
NAMES2=("${NAMES[@]}")

# Concatenate two arrays
NAMES3=("${NAMES[@]}" "${NAMES2[@]}")

# Reverse an array
NAMES=("${NAMES[@]}" | tac)

# Sort an array
NAMES=($(printf '%s\n' "${NAMES[@]}" | sort))

# Read from file
NAMES=($(cat file.txt))

#!/bin/bash

# Define an array
NAMES=("John" "Jane" "Jack")

# Pass the array as arguments
function print_names() {
  for i in "${@}"; do
    echo $i
  done
}

print_names "${NAMES[@]}"

#!/bin/bash

# Define a dictionary
declare -A DICT

# Add dictionary with values
DICT["key1"]="value1"
DICT["key2"]="value2"
DICT["key3"]="value3"

#!/bin/bash

# Pritn by key
echo ${DICT["key1"]}

# Print all values
echo ${DICT[@]}

# Print all keys
echo ${!DICT[@]}

# Length of the dictionary
echo ${#DICT[@]}

# Delete a key2
unset DICT["key2"]

#!/bin/bash

# Iterate over the dictionary
for val in "${DICT[@]}"; do
  echo $val
done

# Iterate over the keys
for key in "${!DICT[@]}"; do
  echo $key
done

# Iterate over the dictionary with keys
for key in "${!DICT[@]}"; do
  echo "$key: ${DICT[$key]}"
done

#!/bin/bash

# String
if [[ -z $STR ]]; then
  echo "Empty string"
elif [[ -n $STR ]]; then
  echo "Not empty"
else
  echo "Not empty"
fi

# Combinations
if [[ $X && $Y ]]; then
  echo "Both are true"
elif [[ $X || $Y ]]; then
  echo "One is true"
else
  echo "Both are false"
fi

# Regex
if [[ $STR =~ ^[0-9]+$ ]]; then
  echo "String is a number"
fi

# Smaller
if [[ $X < $Y ]]; then
  echo "X is smaller than Y"
fi

# Exists
if [[ -f $FILE ]]; then
  echo "File exists"
fi

#!/bin/bash

# Logical and
if [[ $X && $Y ]]; then
  echo "Both are true"
fi

# Logical or
if [[ $X || $Y ]]; then
  echo "One is true"
fi

# Logical not
if [[ ! $X ]]; then
  echo "X is false"
fi

#!/bin/bash

# For loop
for i in {1..10}; do
  echo $i
done

#!/bin/bash

# For loop like C
for ((i=1; i<=10; i++)); do
  echo $i
done

#!/bin/bash

# Ranges
for i in {1..10}; do
  echo $i
done

# Ranges with step
for i in {1..10..2}; do
  echo $i
done

#!/bin/bash

# While loop with auto increment
i=1
while [[ $i -le 10 ]]; do
  echo $i
  ((i++))
done

# While loop with auto decrement
i=10
while [[ $i -ge 1 ]]; do
  echo $i
  ((i--))
done

#!/bin/bash

# Continue
for i in {1..10}; do
  if [[ $i -eq 5 ]]; then
    continue
  fi
  echo $i
done

#!/bin/bash

# Break
for i in {1..10}; do
  if [[ $i -eq 5 ]]; then
    break
  fi
  echo $i
done

#!/bin/bash

# Until loop
i=1
until [[ $i -gt 10 ]]; do
  echo $i
  ((i++))
done

#!/bin/bash

# Infinite loop
while true; do
  echo "Infinite loop"
done

# Infinite loop with (shorthand)
while :; do
  echo "Infinite loop"
done

#!/bin/bash

# Loop over file.txt
while read -r line; do
  echo $line
done < file.txt

#!/bin/bash

# Defining functions
function hello() {
  echo "Hello World"
}

# Defining functions (shorthand), same as above
hello() {
  echo "Hello World"
}

# Calling functions
hello

#!/bin/bash

# Returning values
function myfunc() {
  local myresult='Hello World'
  echo $myresult
}

# Calling functions
result="$(myfunc)"

# Printing result
echo $result

#!/bin/bash

# Raising errors
function myfunc() {
  local myresult='Hello World'
  echo $myresult
  return 1
}

# Calling functions
if myfunc; then
  echo "Success"
else
  echo "Failed"
fi

#!/bin/bash

# Passing arguments
function myfunc() {
  echo "First argument: $1"
  echo "Second argument: $2"
  echo "All arguments: $@"
}

# Calling functions
myfunc "Hello" "World"

#!/bin/bash

# Options

# Disable file overwriting
set -o noclobber

# Exit on error
set -o errexit

# Exit on error in function
set -o errtrace

# Exit on error in function
set -o functrace

# Exit on undefined variable
set -o nounset

# Exit on pipe error
set -o pipefail

# Print commands and their arguments as they are executed
set -o xtrace

# Print shell input lines as they are read
set -o verbose

#!/bin/bash

# Glob options

# Disable globbing and return an empty string if no matches are found
shopt -s nullglob

# Disable globbing and return an empty string if no matches are found
shopt -s failglob

# Include hidden files in globbing
shopt -s dotglob

# Case insensitive globbing
shopt -s nocaseglob

# Enable recursive globbing
shopt -s globstar

# Enable globbing of ASCII character ranges
shopt -s globasciiranges

# Enable extended globbing
shopt -s extglob

#!/bin/bash

# Numeric calculations
echo $(( 1 + 1 ))
echo $(( 1 - 1 ))
echo $(( 1 * 1 ))
echo $(( 1 / 1 ))

# Floating point calculations
echo "scale=2; 1 / 3" | bc

# Random number between 0 and 100
echo $(( RANDOM % 100 ))

#!/bin/bash

# printf
printf "%s\n" "Hello World"

# printf with colors
printf "\033[0;31m%s\033[0m\n" "Hello World"

#!/bin/bash

# Subshells
echo $(date)

# Subshells with variables
date=$(date)

# Change directory in subshell
(cd /tmp && echo "Current directory is: $(pwd)")

#!/bin/bash

# Inspecting commands
command -v ls

# Inspecting commands with arguments
command -v ls -- --help

#!/bin/bash

# Redirection

# Redirect stdout to file
echo "Hello World" > /tmp/hello.txt

# Redirect stdout
node test.js > /tmp/test.txt

# Append stdout
node test.js >> /tmp/test.txt

# Redirect stderr
node test.js 2> /tmp/test.txt

# Append stderr
node test.js 2>> /tmp/test.txt

# Redirect stdout and stderr
node test.js &> /tmp/test.txt

# Append stdout and stderr
node test.js &>> /tmp/test.txt

# Redirect stdout and stderr
node test.js > /tmp/test.txt 2>&1

# Append stdout and stderr
node test.js > /tmp/test.txt 2>&1

#!/bin/bash

# Pipes

# Pipe stdout to stdin
echo "Hello World" | cat

# Pipe stdout and stderr to stdin
node test.js | cat

# Pipe stdout to stdin and stderr to stdout
node test.js 2>&1 | cat

#!/bin/bash

# Process substitution

# Redirect stdout to file
echo "Hello World" > >(cat > /tmp/hello.txt)

# Redirect stdout and stderr to file
node test.js > >(cat > /tmp/test.txt) 2>&1

#!/bin/bash

# Source relative
source "$(dirname "$0")/test.sh"

#!/bin/bash

# Directory of script
DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )"

#!/bin/bash

# Switch/Case
case "$1" in
  start)
    echo "Starting..."
    ;;
  stop)
    echo "Stopping..."
    ;;
  *)
    echo "Usage: $0 {start|stop}"
    exit 1
    ;;
esac

#!/bin/bash

# Trap errors
trap 'echo "Error on line $LINENO"' ERR

# trap 'trapecho "$BASH_COMMAND"' ERR
trapecho() {
  echo "ERROR: ${BASH_SOURCE[1]}:${BASH_LINENO[0]}: ${FUNCNAME[1]}: $1"
}

# trace ERR through 'time command' and other functions
set -o errtrace

# trace ERR through 'time command' and other functions
trap 'trapecho "$BASH_COMMAND"' ERR

#!/bin/bash

# Getting options
while getopts ":a:b:" opt; do
  case $opt in
    a) echo "-a was triggered, Parameter: $OPTARG" >&2
    ;;
    b) echo "-b was triggered, Parameter: $OPTARG" >&2
    ;;
    \?) echo "Invalid option: -$OPTARG" >&2
    ;;
  esac
done

#!/bin/bash

# Check for command's result
if command -v ls &> /dev/null; then
  echo "ls exists"
else
  echo "ls does not exist"
fi

#!/bin/bash

# Grep check
if grep -q "Hello World" /tmp/hello.txt; then
  echo "Hello World exists"
else
  echo "Hello World does not exist"
fi

# Check for file
if [ -f /tmp/hello.txt ]; then
  echo "/tmp/hello.txt exists"
else
  echo "/tmp/hello.txt does not exist"
fi

#!/bin/bash

# Heredoc
cat << EOF
Hello World
EOF

#!/bin/bash

# Reading input
read -p "Enter your name: " name
echo "Hello $name"

#!/bin/bash

# Optional arguments
if [ -z "$1" ]; then
  echo "No arguments supplied"
else
  echo "Argument supplied: $1"
fi

#!/bin/bash

# Strict mode
set -euo pipefail
IFS=$'\n\t'