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Determining The Number Of Array Elements
Using parameter expansion, we can determine the number of elements in an array in much the same way as finding the length of a string. Here is an example:
[me@linuxbox ~]$ a[100]=foo
[me@linuxbox ~]$ echo ${#a[@]} # number of array elements
1
[me@linuxbox ~]$ echo ${#a[100]} # length of element 100
3
[me@linuxbox ~]$ a[100]=foo
[me@linuxbox ~]$ echo ${#a[@]} # number of array elements
1
[me@linuxbox ~]$ echo ${#a[100]} # length of element 100
3
We create array a and assign the string “foo” to element 100. Next, we use parameter ex- pansion to examine the length of the array, using the @ notation. Finally, we look at the length of element 100 which contains the string “foo”. It is interesting to note that while we assigned our string to element 100, bash only reports one element in the array. This differs from the behavior of some other languages in which the unused elements of the ar- ray (elements 0-99) would be initialized with empty values and counted. In bash, array elements only exist if they have been assigned a value regardless of their subscript.