Question

I’m new to Lua programming, having come over from python to basically make a small addon for world of warcraft for a friend. I’m looking into various ways of finding a section of text from a rather large string of plain text. I need to extract the information from the text that I need and then process it in the usual way.

The string of text could be a number of anything, however the below is what we are looking to extract and process

-- GSL --
items = ["itemid":"qty" ,"itemid":"qty" ,"itemid":"qty" ,]
-- ENDGSL --

We want to strip the whole block of text from a potentially large block of text surrounding it, then remove the — GSL — and — ENDGSL — to be left with:

items = ["itemdid":"qty …

I’ve looked into various methods, and can’t seem to get my head around any of them.

Anyone have any suggestions on the best method to tackle this problem?

EDIT: Additional problem,

Based on the accepted answer I’ve changed the code slightly to the following.

function GuildShoppingList:GUILDBANKFRAME_OPENED()
    -- Actions to be taken when guild bank frame is opened.
    if debug == "True" then self:Print("Debug mode on, guild bank frame opened") end
    gslBankTab = GetCurrentGuildBankTab()
    gslBankInfo = GetGuildBankText(gslBankTab)
    p1 = gslBankInfo:match('%-%- GSL %-%-%s+(.*)%s+%-%- ENDGSL %-%-')
    self:Print(p1)
end

The string has now changed slightly the information we are parsing is

{itemid:qty, itemid:qty, itemid:qty, itemid:qty}

Now, this is a string that’s being called in p1. I need to update the s:match method to strip the { } also, and iterate over each item and its key seperated by, so I’m left with

itemid:qty
itemid:qty
itemid:qty
itemid:qty

Then I can identify each line individually and place it where it needs to go.

Answer 1

try

s=[[-- GSL --
items = ["itemid":"qty" ,"itemid":"qty" ,"itemid":"qty" ,]
-- ENDGSL --]]
print(s:match('%-%- GSL %-%-%s+(.*)%s+%-%- ENDGSL %-%-'))

The key probably is that - is a pattern modifier that needs quoting if you want a literal hyphen. More info on patterns in the Lua Reference Manual, chapter 5.4.1

Edit:
To the additional problem of looping through keys of what is almost an array, you could do 2 things:

Either loop over it as a string, assuming both key and quantity are integers:

 p="{1:10, 2:20, 3:30}"
 for id,qty in p:gmatch('(%d+):(%d+)') do
     --do something with those keys:
     print(id,qty)
 end

Or slightly change the string, evaluate it as a Lua table:

 p="{1:10, 2:20, 3:30}"
 p=p:gsub('(%d+):','[%1]=') -- replace : by = and enclose keys with []
 t=loadstring('return '..p)() -- at this point, the anonymous function
                              -- returned by loadstring get's executed
                              -- returning the wanted table
 for k,v in pairs(t) do
     print(k,v)
 end

If the formats of keys or quantities is not simply integer, changing it in the patterns should be trivial.