$ wget https://ip-ranges.amazonaws.com/ip-ranges.json
$ grep ip_prefix ip-ranges.json |
sed -re 's|.*(/[0-9]+).*|\1|' |
sort | uniq -c
4 /11
16 /12
30 /13
82 /14
188 /15
278 /16
70 /17
63 /18
30 /19
47 /20
111 /21
248 /22
204 /23
839 /24
68 /25
235 /26
142 /27
124 /28
50 /29
42 /30
362 /31
370 /32> jq is like sed for JSON data - you can use it to slice and filter and map and transform structured data with the same ease that sed, awk, grep and friends let you play with text.
curl -s https://ip-ranges.amazonaws.com/ip-ranges.json | jq '.prefixes | .[].ip_prefix | .[-3:]' | sort | uniq -cNetmasks might not always be three characters.
Perhaps something like this:
curl -sf https://ip-ranges.amazonaws.com/ip-ranges.json | jq -r '.prefixes[].ip_prefix' | grep -o '/.*' | sort | uniq -c
curl -sf https://ip-ranges.amazonaws.com/ip-ranges.json | jq 'reduce (.prefixes[].ip_prefix | split("/")[1]) as $mask ({}; .[$mask] += 1)'