There are two types of variables in Bash, singular variable and array.
Bash arrays have numbered indexes only, but they are sparse, ie you don’t have to define all the indexes. It can be asigned as an entire array or individual component:
arrayA=(Hello World) or arrayA[0]=Hello arrayA[1]=World
But it gets a bit ugly when you want to refer to an array item:
echo ${arrayA[0]} ${arrayA[1]}
To quote from the man page:
Some useful constructs are:
${arrayA[*]} # All of the items in the array
${!arrayA[*]} # All of the indexes in the array
${#arrayA[*]} # Number of items in the array
${#arrayA[0]} # Length of item zero
The following example shows some simple array usage.
#!/bin/bash
arrayB=(one two three four [5]=five)
n=${#arrayB[*]}
echo "Array size: ${#arrayB[*]} or $n"
echo "Array items:"
for item in ${arrayB[*]}
do
printf " %s\n" $item
done
echo "Array indexes:"
for index in ${!arrayB[*]}
do
printf " %d\n" $index
done
echo "Array items and indexes:"
for index in `seq 0 $n `
do
printf "%4d: %s\n" $index ${arrayB[$index]}
done
Running it produces the following output:
Array size: 5
Array items:
one
two
three
four
five
Array indexes:
0
1
2
3
5
Array items and indexes:
0: one
1: two
2: three
3: four
4:
5: five
Note ${array[*]} can replaced with ${array[@]}
#!/bin/bash
arrayC=("first item" "second item" "third" "item")
echo "Number of items in original array: ${#arrayC[*]}"
for ix in ${!arrayC[*]}
do
printf " %s\n" "${arrayC[$ix]}"
done
echo
arr=(${arrayC[*]})
echo "After unquoted expansion: ${#arr[*]}"
for ix in ${!arr[*]}
do
printf " %s\n" "${arr[$ix]}"
done
echo
arr=("${arrayC[*]}")
echo "After * quoted expansion: ${#arr[*]}"
for ix in ${!arr[*]}
do
printf " %s\n" "${arr[$ix]}"
done
echo
arr=("${arrayC[@]}")
echo "After @ quoted expansion: ${#arr[*]}"
for ix in ${!arr[*]}
do
printf " %s\n" "${arr[$ix]}"
done
When run it outputs:
Number of items in original array: 4
first item
second item
third
item
After unquoted expansion: 6
first
item
second
item
third
item
After * quoted expansion: 1
first item second item third item
After @ quoted expansion: 4
first item
second item
third
item
