Exclusive Pattern Matching In Lua

From this line

frame=    2 fps=  0 q=3.0 size=     开发者_运维知识库 -0kB time=00:00:13.33 bitrate=  -0.0kbits/s dup=0 drop=92

I only want to match the '2' in the frame. How do I accomplish this?

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Here is the Lua pattern string to use:

"frame%=[%s]+(%d+)"

If you use this in a function like string.match, then this will capture the frame number as a string:

local framenumber = string.match(testString, "frame%=%s+(%d+)");

framenumber will either have the captured number (again, as a string. Convert it to a number with tonumber) or NIL if it was not found.

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If frame is always at the beginning and there is always the same amount of spaces you don't actually need patterns. A simple string.sub will do:

local str = "frame=    2 fps= not really important"
local frame = tonumber(str:sub(7,12))

---

Something like this should work.

local data = 'frame=    2 fps=  0 q=3.0 size=      -0kB time=00:00:13.33 bitrate=  -0.0kbits/s dup=0 drop=92'
local _,_, frame = data:find("^frame%=%s+(%d+)")

if frame then
    print("Frame: "..frame)
end 

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Given your comments, the simple pattern s:match("%d+") will work, but s:match("frame=%s*(%d+)") is probably more robust in the long run.