How to extract data for non-fixed string

Question

I have some magnet links being submitted as string in Lua. These magnets normally are of the format:

magnet:?xt=<hashing>&xl=<size>&dn=<name>

but with differences in the clients the magnets can also be generated as:

magnet:?xl=<size>&xt=<hashing>&dn=<name>

From this type of string, I want to fetch the data after xl=(which is pure number) and after xt= which consists of %w and :(where %w is alphanumeric match).

Currently I am using two separate statements to fetch these values. Can this be achieved in a single statement/string.find()?

sInput = "magnet:?xt=urn:tree:tiger:ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABC&xl=1234567890123456789&dn=This+Is+The+Name+Of+File.EXT"
local _, _, sHash = sInput:find( "xt=([%w%:]+)" )
local _, _, iSize = sInput:find( "xl=(%d+)" )

lhf · Accepted Answer · 2012-10-01 13:48:27Z

2

I think you'd be better off collecting all values into a table:

local sInput="magnet:?xt=<hashing>&xl=<size>&dn=<name>"
local s=sInput:match("%?(.*)$").."&"
local t={}
for k,v in s:gmatch("(%w+)=(.-)&") do
        t[k]=v
end

If you want to restrict to the keys starting with x then use gmatch("(x%w+)=(.-)&"). If you know that xt and xl are never the last item in the list, you can simply do:

for k,v in sInput:gmatch("(x%w+)=(.-)&") do

answered Oct 1, 2012 at 13:48

lhf

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1 Comment

Michal Kottman Over a year ago

FYI: he is one of the authors of Lua :)

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