How To Find BASH Shell Array Length ( number of elements )

How do I define bash array?

Array can be defined using following syntax:
ArrayName=("element 1" "element 2" "element 3")
Define array called distro with 3 elements, enter:

distro=("redhat" "debian" "gentoo")

How do I reference any element in bash array?

Any element of an array may be referenced using following syntax:

${ArrayName[subscript]}

To print redhat i.e first element enter:

echo "${distro[0]}"
echo "${distro[2]}"  # will print gentoo

How do I find out bash shell array length?

You can easily find out bash shell array length using following syntax:

${#ArrayName[@]}

To print distro array length enter:

echo "${#distro[@]}"

Sample output:

3

If subscript is @ or *, the word expands to all members of name. By prefixing # to variable you will find length of an array (i.e number of elements). Now we can use bash for loop to read or print values from $distro:

## define it
distro=("redhat" "debian" "gentoo")
 
## get length of $distro array
len=${#distro[@]}
 
## Use bash for loop 
for (( i=0; i<$len; i++ )); do echo "${distro[$i]}" ; done

Putting it all together

A sample shell script to print array called NAMESERVERS:

#!/bin/bash
# define array
# name server names FQDN 
NAMESERVERS=("ns1.nixcraft.net." "ns2.nixcraft.net." "ns3.nixcraft.net.")
 
# get length of an array
tLen=${#NAMESERVERS[@]}
 
# use for loop read all nameservers
for (( i=0; i<${tLen}; i++ ));
do
  echo ${NAMESERVERS[$i]}
done

Sample output:

ns1.nixcraft.net.
ns2.nixcraft.net.
ns3.nixcraft.net.