Lua question: How to use string.match with a string contain a "-"

[dsyrock]

a='#1|1-1.wav#'

path='1-1.wav'

b=a:match('#(%d+)|'..path)

The value of b should be 1, but I got a nil value. Only if I change "1-1" to "11" then b finally gets the correct number.

So what is the correct way to use string.match in this case?

I found a similar question here: https://forum.cockos.com/showthread....t=string.match

But in my case, path could be variable, sometimes it contains a dash sometimes it doesn't.

[cfillion]

- is the metacharacter for 0 or more repetitions (non-greedy) in Lua patterns. Escape it (add a % before) to mean a literal hyphen.

The dot is also a metacharacter (it accepts any one character). It should be escaped too for matching a literal dot.

[Lokasenna]

Since the string is interpreted as a pattern, you have to escape any of the special pattern-matching characters with %:

path = "1%-1.wav"

[dsyrock]

Originally Posted by cfillion

- is the metacharacter for 0 or more repetitions (non-greedy) in Lua patterns. Escape it (add a % before) to mean a literal hyphen.

The dot is also a metacharacter (it accepts any one character). It should be escaped too for matching a literal dot.

But in my case, the value of path is from a media item, how can i change it to the prober format?

[cfillion]

Either search/replace each occurrence of a Lua pattern matacharacter to escape them (eg. using string.gsub) or find another way that doesn't involve using string.match with an arbitrary string. What is the root problem/feature this is intended to solve?

[Lokasenna]

local function escapePercent(str) 
  return str:gsub("%-", "%%-") 
end

b = a:match("#(%d+)|" .. escapePercent(path))

You can chain :gsub as many times as you want with the same logic to escape any other special characters.

[dsyrock]

Originally Posted by cfillion

Either search/replace each occurrence of a Lua pattern matacharacter to escape them (eg. using string.gsub) or find another way that doesn't involve using string.match with an arbitrary string. What is the root problem/feature this is intended to solve?

Thanks!

[dsyrock]

Originally Posted by Lokasenna

local function escapePercent(str) 
  return str:gsub("%-", "%%-") 
end

b = a:match("#(%d+)|" .. escapePercent(path))

You can chain :gsub as many times as you want with the same logic to escape any other special characters.

It works, thanks! By the way, I did something similar before

path=path:gsub('-', '%-')

Then I realize that is not allowed. Now you showed me the right way.

[dsyrock]

Then one more question. For instance, there are stringA and stringB, and stringB is a completely random string. If I'm gonna do something like stringA:match(stringB), do I have to replace all the magic characters in stringB for safety?

function escape(text)
    text=text:gsub('%-', '%%-')
    text=text:gsub('%.', '%%.')
    etc

    return text
end

stringA:match(escape(stringB))

[cfillion]

If all you need is checking whether stringA contains stringB, string.find has a "plain" parameter which entirely disables pattern matching when set to true:

stringA:find(stringB, 1, true) -- no need to escape stringB

[dsyrock]

Originally Posted by cfillion

If all you need is checking whether stringA contains stringB, string.find has a "plain" parameter which entirely disables pattern matching when set to true:

stringA:find(stringB, 1, true) -- no need to escape stringB

Thanks, but I do need the match function, as the example I post at #1. It would be better if string.match has a plain mode.

[Lokasenna]

string.match doesn't have a plain option, so if you specifically need match you'll have to run string B through the escape function above.

[Meo-Ada Mespotine]

Is there a function floating in this forum somewhere, where the escaping of a magic characters in such a string can be made?
So the resulting string can be used for plain-matching? I think, it would be a nice addition for my API.

[cfillion]

http://stackoverflow.com/a/34953646

[Meo-Ada Mespotine]

Thanks