How to check if a IP (ipv4) address is valid in pure Bash
Here is a small bash function to check if a IP is valid (4 octets, each octet < 256). I find it somewhat elegant since instead of using a lot of case/if/then constructs or a crazy long regex it splits the IP into each octet (and stores them in an array, and then uses a combination of regex and bit shifting to check each octet.
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is_valid_ipv4() {
local -a octets=( ${1//\./ } )
local RETURNVALUE=0
# return an error if the IP doesn't have exactly 4 octets
[[ ${#octets[@]} -ne 4 ]] && return 1
for octet in ${octets[@]}
do
if [[ ${octet} =~ ^[0-9]{1,3}$ ]]
then # shift number by 8 bits, anything larger than 255 will be > 0
((RETURNVALUE += octet>>8 ))
else # octet wasn't numeric, return error
return 1
fi
done
return ${RETURNVALUE}
}
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The function will return 0 if the IP is valid, and 1 or higher if it encountered an error (you can check with the $? variable directly after calling the function)
Example:
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is_valid_ipv4 ${ip}
if [[ $? -gt 0 ]]
then
echo "invalid IP"
else
echo "valid IP"
fi
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