[Lua][Question] shell.resolve help

function shell.resolve( _sPath )
local sStartChar = string.sub( _sPath, 1, 1 )
if sStartChar == "/" or sStartChar == "" then
return fs.combine( "", _sPath )
else
return fs.combine( sDir, _sPath )
end
end

function shell.resolveProgram( _sCommand )
-- Substitute aliases firsts
if tAliases[ _sCommand ] ~= nil then
_sCommand = tAliases[ _sCommand ]
end

-- If the path is a global path, use it directly
local sStartChar = string.sub( _sCommand, 1, 1 )
if sStartChar == "/" or sStartChar == "" then
local sPath = fs.combine( "", _sCommand )
if fs.exists( sPath ) and not fs.isDir( sPath ) then
return sPath
end
return nil
end

-- Otherwise, look on the path variable
for sPath in string.gmatch(sPath, "[^:]+") do
sPath = fs.combine( shell.resolve( sPath ), _sCommand )
if fs.exists( sPath ) and not fs.isDir( sPath ) then
return sPath
end
end

-- Not found
return nil
end