Looping through an array in shell script

Generally speaking, when I need to work with an array or dictionary type of
variable, I tend to reach for something other than Bash / shell scripting.

This primarily stems from the fact that Bash didn’t support arrays until version
4.x and when I first learned about them, macOS (then OS X) was still shipping
with version 3.x which didn’t support them.

Fast forwarded a few years, macOS is shipping with Z Shell and I am back to
using Linux as my daily driver.

So all that said, even though I prefer to use a scripting language like
JavaScript when I need more complex variables, there are times when I have an
existing shell script that I’d rather not port over.

Let’s say you have a list of IP addresses you want to run through and run nmap
against each one, first you’d define an array that looks something like this:


Still weirds me out to define an array without a comma , between each item.

If you’re using Z Shell like I do, you can easily dump out the contents of the
entire array using echo like it’s any other variable:


Which will display ll of the entries in the array, space delimited. With Bash,
you’ll only get the first item of the array, sad face.

It doesn’t take much to loop through the items once the variable is defined:

for IP_ADDRESS in "${IP_ADDRESSES[@]}" do
  # Swap `echo` for `nmap` to actually scan
  echo "$IP_ADDRESS"

Great, each IP address is displayed or you swapped echo for nmap and you’re
waiting for the scan of each IP address to complete!

Josh Sherman - The Man, The Myth, The Avatar

About Josh

Husband. Father. Pug dad. Musician. Founder of Holiday API, Head of Engineering and Emoji Specialist at Mailshake, and author of the best damn Lorem Ipsum Library for PHP.

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