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regex='(?>(?>([a-f\d]{1,4})(?>:(?1)){3}|(?!(?:.*[a-f\d](?>:|$)){})((?1)(?>:(?1)){0,6})?::(?2)?)|(?>(?>(?1)(?>:(?1)){5}:|(?!(?:.*[a-f\d]:){6,})(?3)?::(?>((?1)(?>:(?1)){0,4}):)?)?(25[0-5]|2[0-4]\d|1\d{2}|[1-9]?\d)(?>\.(?4)){3}))\/\d{1,2}'
txt="v=abc ip4:127.0.0.1/19 ip4:192.168.1.1/32 ip4:192.168.2.50/20 ip6:2001:4860:4000::/36 ip6:2404:6800:4000::/36 ip6:2607:f8b0:4000::/36 ip6:2800:3f0:4000::/36 ip6:2a00:1450:4000::/36 ip6:2c0f:fb50:4000::/36 ~all"
echo "$txt" | grep -Po "$regex"