Bash

The "Bourne-again shell" (Bash) is a command language and interpreter on Unix systems.

#!/usr/bin/env bash
# hello beer: drink 0.5 liter in 4 rounds

LITER_PER_SIP=$(bc <<< "scale=3; 37/1000")
ROUNDS=4

function sips2liter(){
    echo $(bc <<< "scale=3; $1 * ${LITER_PER_SIP}")
}

beer_l=0.5
sips_per_round=(3 7 4 2)

echo "I drink ${beer_l} l in ${ROUNDS} rounds:"
for sips in ${sips_per_round[@]}
do
    echo "I drink ${sips} sips."
    sleep ${sips}s
    consumed_l=$(sips2liter ${sips})
    beer_l=$(bc <<< "scale=3; ${beer_l} - ${consumed_l}" )
    if [[ $(bc <<< "${beer_l} <= 0.0") -eq 1 ]]; then
        echo "My beer is empty!"
        break
    else
        echo "I have ${beer_l} l beer left."
    fi
done
exit 0

Data Structures

Arrays
Create (space separated): arr=(one two 42)
Access: ${arr[0]} one

Numbers
Bash only supports Integers! Float expressions need to be parsed by an external binary such as bc.

String Manipulations

• Slicing new=${old:12:5} where 12 is the offset (zero-based) and 5 is the length

mystr="what_is_this"
tmp=${mystr#*_}   # remove prefix ending in "_"
final=${tmp%_*}   # remove suffix starting with "_"
echo ${final}     # output "is"

Control Flow

Comparators (Test)

if [[ ${var} -eq 1 ]]; then
    # do stuff
fi

• Integer: -eq, -ne, -lt, -gt, -le, -ge
• Strings: ==, !=, <, \>
• Files: -f, -d, -r, -w, -x

Input / Output

read -p "Do you want to continue? (y|n)" -n 1 -r
if [[ $REPLY =~ ^[Yy]$ ]]; then
    # do dangerous stuff
fi

# read file line by line
while read f; do
    echo "Line is $f"
done < $path
}