Parse nginx access log and extract IP, detect geo location for each parsed IP

The syntax <<< grep "pagename" <<< "$line0" is slighly off, <<<X inputs the string X to the stdin.

The syntax you want is the process substitution syntax (combined with a redirection-arrow):

< <(grep "pagename" <<< "$line0")

Here's also a simpler solution:

#! /bin/bashwhile read -r oneIP; do    curl -s "http://ipinfo.io/$oneIP"done < <(grep "pagename" /var/log/nginx/access.log \         | grep -oP '\b(?:(?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2}))\b')

The result of the first grep is piped to the second, and that stream of ips is then redirected to the while-loop which runs the curl for each of the ips.

You could also parallelize this with something like gnu parallel:

#! /bin/bashgrep "pagename" /var/log/nginx/access.log \| grep -oP '\b(?:(?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2}))\b' \| parallel echo curl -s "http://ipinfo.io/"{}