bash-scrip-cheatsheet

Arrays

Creating an array in Bash

1. Declare without adding elements

   declare -a my_first_array

2. Create and add at the same time

   my_first_array=(1 2 3) # remember: No commas!

Important array properties

• All array elemnts can be return using array[@]. though do note, Bash requires curly brackets around the array name when you want to access these properties

my_array=(1 3 5 2)
echo ${my_array[@]}
>> 1 3 5 2

• The length of an array is accessed using #array[@]

${#my_array[@]}

Manipulating array elements

• accessing array elements using square brackets.

my_first_array=(15 20 300 42)
echo ${my_first_array[2]}
>> 300

• Set array elements using the index notation.

my_first_array=(15 20 300 42 23 2 4 33 54 67 66)
my_first_array[0]=999
echo ${my_first_array[0]}
>>999

• Use the notation array[@]:N:M to "slice" out a subset of the array.

my_first_array=(15 20 300 42 23 2 4 33 54 67 66)
echo ${my_first_array[0]:3:2}
>>42 23

• Append to an array using array+=(elements)

my_first_array=(15 20 300 42 23 2 4 33 54 67 66)
my_first_array+=(10) # if you forget the parenthesis a 10 will be concatenated to the first element

Associative arrays

Similar to Python dictionaries

Creating an associative array

You can only create an associative array using the declare syntax (and uppercase -A). You can either declare first, then add elements or do it all on one line. e.g.

declare -A city_details # Declare first
city_details=([city_name]="New York" [population]=14000000) # Add elements
echo {city_details[city_name]} # Index using key to return a value
>> New York

declare -A city_details=([city_name]="New York" [population]=14000000)

You can access the keys of an associative array with an !

echo ${!city_details[@]} # return all the keys
>> city_name population