name="John"
echo $name    # Basic output
echo "$name"  # Recommended way (with quotes)
echo "${name}"  # Most explicit way

echo "Current directory: $(pwd)"   # Modern syntax
echo "Current directory: `pwd`"    # Legacy syntax

git commit && git push             # Run second command only if first succeeds
git commit || echo "Commit failed" # Run second command only if first fails

get_name() {
    echo "John"
}
echo "You are $(get_name)"

if [[ -z "$string" ]]; then
    echo "String is empty"
elif [[ -n "$string" ]]; then
    echo "String is not empty"
fi

name="John"
echo "${name}"           # Standard output
echo "${name/J/j}"      # Substitution (john)
echo "${name:0:2}"      # Slicing (Jo)
echo "${name::2}"       # Slicing from start (Jo)
echo "${name::-1}"      # Slice except last char (Joh)
echo "${name:(-1)}"     # Last character (n)
echo "${food:-Cake}"    # Default value if unset

str="/path/to/foo.cpp"
echo "${str%.cpp}"      # Remove .cpp
echo "${str%.cpp}.o"    # Replace with .o
echo "${str%/*}"        # Remove last segment
echo "${str##*.}"       # Get extension
echo "${str##*/}"       # Get filename
echo "${str#*/}"        # Remove first segment
echo "${str/foo/bar}"   # Replace foo with bar

# Definition
Fruits=('Apple' 'Banana' 'Orange')

# Access
echo "${Fruits[0]}"     # First element
echo "${Fruits[-1]}"    # Last element
echo "${Fruits[@]}"     # All elements
echo "${#Fruits[@]}"    # Number of elements
echo "${#Fruits}"       # Length of first element

# Modification
Fruits+=('Watermelon')  # Add element
unset Fruits[2]         # Remove element
Fruits=("${Fruits[@]}") # Recreate array

# Declaration
declare -A sounds
sounds[dog]="bark"
sounds[cow]="moo"

# Access
echo "${sounds[dog]}"   # Single value
echo "${sounds[@]}"     # All values
echo "${!sounds[@]}"    # All keys
echo "${#sounds[@]}"    # Number of elements

[[ -e FILE ]]    # Exists
[[ -r FILE ]]    # Readable
[[ -h FILE ]]    # Symlink
[[ -d FILE ]]    # Directory
[[ -w FILE ]]    # Writable
[[ -s FILE ]]    # Size > 0 bytes
[[ -f FILE ]]    # Regular file
[[ -x FILE ]]    # Executable

[[ -z STRING ]]          # Empty string
[[ -n STRING ]]          # Not empty string
[[ STRING == STRING ]]   # Equal
[[ STRING != STRING ]]   # Not equal
[[ STRING =~ REGEX ]]    # Regex match

[[ NUM -eq NUM ]]   # Equal
[[ NUM -ne NUM ]]   # Not equal
[[ NUM -lt NUM ]]   # Less than
[[ NUM -le NUM ]]   # Less than or equal
[[ NUM -gt NUM ]]   # Greater than
[[ NUM -ge NUM ]]   # Greater than or equal

# Basic for loop
for i in /etc/rc.*; do
    echo "$i"
done

# C-style for loop
for ((i = 0; i < 100; i++)); do
    echo "$i"
done

# Range loop
for i in {1..5}; do
    echo "Welcome $i"
done

# With step size
for i in {5..50..5}; do
    echo "Welcome $i"
done

# Reading lines
while read -r line; do
    echo "$line"
done <file.txt

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

command > output.txt      # stdout to file
command >> output.txt     # stdout to file (append)
command 2> error.log      # stderr to file
command 2>&1             # stderr to stdout
command &>/dev/null      # stdout and stderr to null

echo -n "Proceed? [y/n]: "
read -r ans
echo "$ans"

read -n 1 ans    # Read single character

$?      # Exit status of last command
$!      # PID of last background process
$$      # Current shell PID
$0      # Script name
$_      # Last argument of previous command
$#      # Number of arguments
$@      # All arguments as separate words
$*      # All arguments as a single word

set -euo pipefail
IFS=$'\n\t'

trap 'echo Error at about $LINENO' ERR

# Or with function
traperr() {
    echo "ERROR: ${BASH_SOURCE[1]} at about ${BASH_LINENO[0]}"
}
set -o errtrace
trap traperr ERR

case "$1" in
    start|up)
        vagrant up
        ;;
    stop|down)
        vagrant halt
        ;;
    *)
        echo "Usage: $0 {start|stop}"
        ;;
esac

cat <<END
hello world
END

result=$(command)
lines=(`cat "logfile"`)