bash-array

Index Array (Lists)

This is similar to python lists, to declare a list

mylist=( str 2 3 text 3 "with space" 'more" space' )

declare -a mylist

• the syntax is using () and the delimiter is space, if there are spaces, it needs to be quoted

Getting value from list

• by default only the first item will be echoed, use [@] to get everything in the list as multiple variables
• the list index is obtained using !mylist
• the way to get item from list is same as Python using [index]

$mylist # first list item
${mylist[@]} # entire list
${!mylist[@]} # get all the index
${mylist[-1]} # last list item

Lists are mutable, items can be changed or added

mylist[0]="mystr"

To add item in list to the end, similar to append

mylist+=( "item" 2 )

Get the length of the list

echo ${#mylist[@]}

To remove a list, use unset, can remove items or entire array

unset mylist[1]

• when the item is unset, even the index is removed and it is not continuous
  List splicing
  Bash list splicing is different, it has a start index and length (not end index)

${newlist[@]:index:length}

• index is the starting index (inclusive)
• length indicate how many items from the starting index to include

Bash Dictionary

This is similar to Python dictionaries, to declare a dictionary (associative array):

declare -A mydict
mydict=( [key1]="value1" [key2]="value2" [key3]="value3" )

• use declare -A for associative arrays
• keys and values are assigned using [key]=value syntax

Getting values from dictionary:

• access value by key: ${mydict[key1]}
• get all keys: ${!mydict[@]}
• get all values: ${mydict[@]}

echo ${mydict[key1]}      # value for key1
echo ${!mydict[@]}        # all keys
echo ${mydict[@]}         # all values

Add or update key-value pairs:

mydict[newkey]="newvalue"

Remove a key-value pair:

unset mydict[key2]

Get the number of key-value pairs:

echo ${#mydict[@]}