Generating a list of IP addresses in a Bash loop

Question

I need a list of IP addresses from 130.15.0.0 to 130.15.255.255. I tried this but I realized it will create 255 lists. Can anyone please help me figure this out?

for (( i = 0; i <= 255; i++)) ; do
for (( j = 0; j <= 255; j++)) ; do
LIST="$LIST 130.15.$i.$j"
done
done

Answer 1

I'd say that your approach works, but it is very slow¹. You can use brace expansion instead:

echo 135.15.{0..255}.{0..255}

Or, if you want the result in a variable, just assign:

list=$(echo 135.15.{0..255}.{0..255})

If you want the addresses in an array, you can skip the echo and command substitution:

list=(135.15.{0..255}.{0..255})

Now, list is a proper array:

$ echo "${list[0]}"                    # First element
135.15.0.0
$ echo "${list[@]:1000:3}"             # Three elements in the middle
135.15.3.232 135.15.3.233 135.15.3.234

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Comments on your code:

• Instead of

  list="$list new_element"
  

  it is easier to append to a string with

  list+=" new_element"
  

• If you wanted to append to an array in a loop, you'd use

  list+=("new_element")
  

• Uppercase variable names are not recommended as they're more likely to clash with environment variables (see POSIX spec, paragraph four)

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¹ In fact, on my machine, it takes almost six minutes – the brace expansion takes less than 0.1 seconds!