Getting started

myarr=()             #Make an empty array
myarr=(a b c 3 2 1)  #Initialize an array
${myarr[4]}          #Getting 5th element
${myarr[@]}          #Getting all emements
${!myarr[@]}         #Getting indices
${#myarr[@]}         #Getting length
myarr[2]=3           #Modify 3nd element
myarr+=(x y z)       #Append elements
myarr=( $(ls) )      #Save `ls` out as an array
${myarr[@]:s:n}      #Retrieve n elements beginning at index s
unset myarr[0]       #Destroy 1st element
unset myarr          #Remove the entire array

Looping array elements

${myarr[@]}stands to all members of the array myarr ,so you can use for command to loop array elements

$myarr=(a b c 3 2 1)
$for x in ${myarr[@]}; do echo $x; done

Looping array indices

${!myarr[@]} stands the index of array myarr , starts at zero .

$myarr=(a b c 3 2 1)
$for i in ${!myarr[@]}; do echo "indice $i = ${myarr[i]}"; done
indice 0 = a
indice 1 = b
indice 2 = c
indice 3 = 3
indice 4 = 2
indice 5 = 1

$* vs $@

For array both @ and * expands all the elements of an array ,but they differ only when the word appears within double quotes.${arr[*]} expands to a single word with the value of each array member by IFS (space by default), and ${name[@]} expands each element of name to a separate word.

$arr=(1 "Hello world" 2)
$for x in "${arr[*]}"; do echo $x; done
1 Hello world 2
$for x in "${arr[@]}"; do echo $x; done
Hello world
  • Note the Hello world been quoted.

Associative array (dictionary)

declare -A dict         #Declare an associative arry
declare -A dict=( [key1] value1 [key2] value2 )
dict['key3']='value3'   #Add or modify element
${dict[@]}              #expand the values
${!animals[@]}          #expand the keys

For example:

$declare -A dict=( [key1]=value1 [key2]=value2 )
$echo ${dict[key2]}
$echo ${dict[@]}
value2 value1
$echo ${!dict[@]}
key2 key1