Cheat sheet verified with Bash 4.4.19

Variables

Set and get

local var="Jan"
echo $var

Arrays

Indexed - Standard arrays with number as index array_var=(value1 value2 value3)

Associative - Index could be any string array_var=([text-index]=value [text-index2]=value2)

Declare

Indexed

array_var=()

array_var=(value1 value2 value3)

declare -a array_var

Associative

declare -A array_var

Conversion from String

Convert string to array. With space separator " “

var_string='string is automatically converted'
array=( "$var_string" )
echo ${array[0]}

Print/Get array elements

Get first array element

array=(value1 value2 value3)
echo ${array[1]}
`value1`

Get all array elements

array=(value1 value2 value3)
echo ${array[@]}

Get array size

echo "${#array[@]}"

Get index of array element

array=(feb may jan)
value='jan'

for i in "${!array[@]}"; do
   if [[ "${array[$i]}" = "${value}" ]]; then
       echo "${i}";
   fi
done

Output:

2

Merge arrays

combined=( "${array1[@]}" "${array2[@]}" )

Merge arrays and remove duplicates

no_duplicates=( $(printf '%s\n' "${array[@]}" | sort -uz) )

Check if array contains some value

function contains(){
        if [[ " ${some_array[@]} " =~ " ${some_value} " ]]; then
          echo "FOUND"
        else
          echo "NOT FOUND"
        fi
}

Conditionals

Simple if else

if [ "true" = "false" ] then
    echo You may go to the party.
elif [ "false" == "true" ] then
    echo You may go to the party but be back before midnight.
else
    echo You may not go to the party.
fi

test command => In conditionals: []

value=0
[[ $(test $value) -eq 1 ]] || echo "Condition not fulfilled."

Output:

Condition not fulfilled.

String operations

Replace space with new line

echo "String with spaces"  | tr ' ' '\n'

Output:

String
with
spaces

Substitute words in variable:

name="Marko"
grade=5
input="Hello I'm #name. My grade is #grade."
command=$(echo "$input" | sed "s/#name/$name/gi" | sed "s/#grade/$grade/gi")
echo $command

Output:

Hello I'm Marko. My grade is 5.

Files

for through files in path

for path in /some/path/*; do
    readFile "${path}"
done

Read line in a file with empty lines, spaces and comments removal

sed -e 's/[[:space:]]*#.*// ; /^[[:space:]]*$/d' $1 | while IFS= read -r line || [ -n "$line" ];
do
    echo $line
done

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