how to find the index of a repeated character in lua string

Question

suppose you have a path like this /home/user/dev/project I want to get the index of any / I want
like if I want the one before dev or the one before user
I don't get lua string patterns if there is a good documentation for it please link it

Answer 1

There are several ways to do this. Perhaps the simplest is using the () pattern element which yields a match position combined with string.gmatch:

for index in ("/home/user/dev/project"):gmatch"()/" do
    print(index)
end

which prints

1
6
11
15

as expected. Another way to go (which requires some more code) would be repeatedly invoking string.find, always passing a start index.

Assuming that you probably want to split a string by slashes, that's about as simple using string.gmatch:

for substr in ("/home/user/dev/project"):gmatch"[^/]+" do
    print(substr)
end

(the pattern finds all substrings of nonzero, maximal length that don't contain a slash)

Documentation for patterns is here. You might want to have a look at the subsection "Captures".

Answer 2

There are many ways to do so.
Also its good to know that Lua has attached all string functions on datatype string as methods.
Thats what @LMD demonstrates with the : directly on a string.
My favorite place for experimenting with such complicated/difficult things like pattern and their captures is the Lua Standalone Console maked with: make linux-readline
So lets play with the pattern '[%/\\][%u%l%s]+'

> _VERSION
Lua 5.4
> -- Lets set up a path
> path='/home/dev/project/folder with spaces mixed with one OR MORE Capitals in should not be ignored'
> -- I am curious /home exists so trying to have a look into
> os.execute('/bin/ls -Ah ' .. ('"%s"'):format(path:match('[%/\\][%u%l%s]+')));
knoppix  koyaanisqatsi
> -- OK now lets see if i can capture the last folder with the $
> io.stdout:write(('"%s"\n'):format(path:match('[%/\\][%u%l%s]+$'))):flush();
"/folder with spaces mixed with one OR MORE Capitals in should not be ignored"
> -- Works too so now i want to know whats the depth is
> do local str, count = path:gsub('[%/\\][%u%l%s%_%-]+','"%1"\n') print(str) return count end
"/home"
"/dev"
"/project"
"/folder with spaces mixed with one OR MORE Capitals in should not be ignored"

4
> -- OK seems usefull lets check a windows path with it
> path='C:\\tmp\\Some Folder'
> do local str, count = path:gsub('[%/\\][%u%l%s]+','<%1>') print(str) return count end
C:<\tmp><\Some Folder>
2
> -- And that is what i mean with "many"
> -- But aware that only lower upper and space chars are handled
> -- So _ - and other chars has to be included by the pattern
> -- Like: '[%/\\][%u%l%s%_%-]+'
> path='C:\\tmp\\Some_Folder'
> do local str, count = path:gsub('[%/\\][%u%l%s%_%-]+','<%1>') print(str) return count end
C:<\tmp><\Some_Folder>
2
> path='C:\\tmp\\Some-Folder'
> do local str, count = path:gsub('[%/\\][%u%l%s%_%-]+','<%1>') print(str) return count end
C:<\tmp><\Some-Folder>
2