Lua. Search string in a file and print second column - regex

Question

Looking for solution to replace following command in Lua:
grep "dhcp-range" /tmp/etc/dnsmasq.conf | awk -F "\"*,\"*" '{print $2}'
tried
for line in file:lines() do
if line:match("([^;]*),([^;]*),([^;]*),([^;]*),([^;]*)") then
print(line[2])
end
end
and it doesnt work.
/tmp/etc/dnsmasq.conf looks like this
dhcp-leasefile=/tmp/dhcp.leases
resolv-file=/tmp/resolv.conf.auto
addn-hosts=/tmp/hosts
conf-dir=/tmp/dnsmasq.d
stop-dns-rebind
rebind-localhost-ok
dhcp-broadcast=tag:needs-broadcast
dhcp-range=lan,192.168.34.165,192.168.34.179,255.255.255.0,12h
no-dhcp-interface=eth0

Answer 1

Here is a function in Lua that will print the values you need if you pass the whole file contents to it:
function getmatches(text)
for line in string.gmatch(text, "[^\r\n]+") do
m,n = string.match(line,"^dhcp%-range[^,]*,([^,]+),([^,]+)")
if m ~= nil then
print(m,n)
end
end
end
See Lua demo
With string.gmatch(text, "[^\r\n]+"), each file line is accessed (adjust as you see fit), and then the main part is m,n = string.match(line,"^dhcp%-range[^,]*,([^,]+),([^,]+)") that instantiates m with the first IP and n with the second IP found on a line that starts with dhcp-range.
Lua pattern details:
^ - start of string
dhcp%-range - a literal string dhcp-range (a - is a quantifier in Lua matching 0 or more occurrences, but as few as possible, and to match a literal -, it must be escaped. Regex escapes are formed with %.)
[^,]*, - 0+ chars other than , and then a ,
([^,]+) - Group 1 (m): one or more chars other than ,
, - a comma
([^,]+) - Group 1 (n): one or more chars other than ,.

Answer 2

Try this code:
for line in io.lines() do
local a,b=line:match("^dhcp%-range=.-,(.-),(.-),")
if a~=nil then
print(a,b)
end
end
The pattern reads: match dhcp-range= at the start of a line (note the need to escape - in Lua), skip everything until the next comma, and capture the next two fields between commas.