Callbacks

Converters

argparse can perform automatic validation and conversion on arguments. If convert property of an element is a function, it will be applied to all the arguments passed to it. The function should return nil and, optionally, an error message if conversion failed. Standard tonumber and io.open functions work exactly like that.

parser:argument "input"
   :convert(io.open)
parser:option "-t --times"
   :convert(tonumber)

$ lua script.lua foo.txt -t5

{
   input = file_object,
   times = 5
}

$ lua script.lua nonexistent.txt

Usage: script.lua [-t <times>] [-h] <input>

Error: nonexistent.txt: No such file or directory

$ lua script.lua foo.txt --times=many

Usage: script.lua [-t <times>] [-h] <input>

Error: malformed argument 'many'

Table converters

If convert property of an element is a table, arguments passed to it will be used as keys. If a key is missing, an error is raised.

parser:argument "choice"
   :convert {
      foo = "Something foo-related",
      bar = "Something bar-related"
   }

$ lua script.lua bar

{
   choice = "Something bar-related"
}

$ lua script.lua baz

Usage: script.lua [-h] <choice>

Error: malformed argument 'baz'

Actions

argparse can trigger a callback when an option or a command is encountered. The callback can be set using action property. Actions are called regardless of whether the rest of command line arguments are correct.

parser:argument "required_argument"

parser:flag("-v --version", "Show version info and exit.")
   :action(function()
      print("script.lua v1.0.0")
      os.exit(0)
   end)

$ lua script.lua -v

script.lua v1.0.0