Pasted

local args = {...}
 
if #args == 0 then
    error("usage: which <program>", 0)
end
 
local result = shell.resolveProgram(args[1])
 
if result == nil then
    error(table.concat {
        '"',
        args[1],
        '" not found'
    }, 0)
end
 
write '/'
print(result)