From 1c9ef1f8a936d71c19ff07149e97e443923fc7fd Mon Sep 17 00:00:00 2001
From: Aaron Ball <nullspoon@oper.io>
Date: Fri, 2 Nov 2018 10:50:23 -0600
Subject: Added IPv4 validity check

This adds the is_ipv4 function that checks the input string for ipv4
validity. Main function will now exit early if provided IP is invalid.
---
 dnsbl-check.sh | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/dnsbl-check.sh b/dnsbl-check.sh
index f3632bd..9e202b6 100755
--- a/dnsbl-check.sh
+++ b/dnsbl-check.sh
@@ -25,6 +25,23 @@ export CRESET=$'\e[0m'
 
 export LIST=${LIST:-dnsbls.txt}
 
+# is_ipv4:
+# Checks if the provided string is a valid IPv4 address.
+#
+# @str   String to check
+# @return (stdout) 1 == valid ip, 0 == invalid ip
+is_ipv4() {
+  local str="${1}"
+  local match
+  match=$(printf "${str}" | grep -E '^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$')
+  if [ "${match}" = "${str}" ]; then
+    printf 1
+    return 0;
+  fi
+  printf 0;
+  return 1;
+}
+
 
 # main:
 # Ye olde' main.
@@ -49,6 +66,11 @@ main() {
     dnsbls=($(grep -v '^#' "${LIST}"))
   fi
 
+  if [ $(is_ipv4 "${ip}") = 0 ]; then
+    printf "Provided IP '%s' is not a valid IPv4 address\n" "${ip}"
+    return 1
+  fi
+
   # If the terminal is not a char terminal (eg: someone is using less, more,
   # cat, etc), we don't want to print escape codes because they will get
   # mangled by the tool most likely.
-- 
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