Bash scripts

Arithmetic expansion

$((expression))
 
echo $(( 4 + 2 ))
y=4
x=2
echo $(( $y + $x ))
echo $(( y + x ))
$(( 4 ** 2)) # 4 to the power of 2

bc command

echo "5/2" | bc
echo "scale=2; 5/2" | bc # scale: number of decimal digits

Command Substitution

$(command)

time=$(date +%H:%m:%S)

History Expansion

Shell Parameters

How Bash process command line