what does "(.+)"}], in lua pattern matching mean

Question

i got this code that take webhook message but i dont understand the pattern matching behind it

function getContent(link)
    cmd = io.popen('powershell -command "[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12; Write-Host (Invoke-WebRequest -Uri "'..link..'").Content"')
    return cmd:read("*all"):match('"description": "(.+)"}],')
end

function blabla(a)
    link= webhookLink.."/messages/"..messageId
    text = [[
        $webHookUrl = "]]..link..[["
        $embedObject = @{
            description = "]]..getContent(link):gsub("\\([nt])", {n="\n", t="\t"})..[[`n]]..a..[["
        }
        $embedArray = @($embedObject)
        $payload = @{
            embeds = $embedArray
        }
        [Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12
        Invoke-RestMethod -Uri $webHookUrl -Body ($payload | ConvertTo-Json -Depth 4) -Method Patch -ContentType 'application/json'
    ]]
    file = io.popen("powershell -command -", "w")
    file:write(text)
    file:close()
end

My question is what does "(.+)"}] mean in the getContent function and ]]..getContent(link):gsub("\\([nt])", {n="\n", t="\t"})..[[n]]..a..[[inblabla` function ?

it is all in the manual. what stops you from reading it? – Piglet Nov 14 '22 at 16:28 — Piglet, Nov 14 '22 at 16:28

AMR · Answer 1 · 2022-11-14T14:07:30.583

1

https://gitspartv.github.io/lua-patterns/ This can help you greatly with pattern matching,

though, (.+) means capture any digit, with multiple repetations.

example: "ABC(.+)" would return everything after "ABC"

return cmd:read("*all"):match('"description": "(.+)"}],') Looks like this gets everything inside description: "THIS_IS_RETURNED"],

edited Nov 14 '22 at 14:07

answered Nov 14 '22 at 14:04

AMR

11
3

score 1 · Answer 2 · answered Nov 14 '22 at 16:06

Let's break up the pattern: "description": "(.+)"}],

"description": " - literal string that needs to match
(.+) - one or more of any character, greedy (+), captured
"}], - another literal string

That is, this pattern will match the first substring that starts with "description": ", followed by one or more characters which are captured, followed by "}],.

All in all, this pattern is a very unreliable implementation of extracting a certain string from what's probably JSON; you should use a proper JSON parser instead. This pattern will fail in all of the following cases:

Empty String: [[{"description": ""}],null] (might be intended)
Another String later on: [{"foo": [{"description": "bar"}], "baz": "world"}], null], which would match as bar"}], "baz": "world due to + doing greedy matching.

ahh okay why + is greedy ? also ]]..getContent(link):gsub("\\([nt])", {n="\n", t="\t"})..[[n]]..a..[[ for this iam trying to dechiper also what pattern is that matching — Retaker, Nov 15 '22 at 03:14
`+` is greedy per definition. Refer to the [reference manual](https://www.lua.org/manual/5.1/manual.html#5.4.1). `\([nt])` matches a backslash followed by an `n` or `t`, which is captured (JSON string escapes). `str:gsub("\([nt])", {n="\n", t="\t"})` will replace the escape sequence `\n` with a newline character and the escape sequence `\t` with a tab. — Luatic, Nov 15 '22 at 07:54

score -1 · Answer 3 · answered Nov 14 '22 at 13:55

-1

. means any character, and + means one or more. I suggest you to read up on the basics of patterns. For example: http://lua-users.org/wiki/PatternsTutorial

answered Nov 14 '22 at 13:55

Ivo

18,659
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what does "(.+)"}], in lua pattern matching mean

3 Answers3