| ARGPARSE(1) | argparse | ARGPARSE(1) |
argparse - argparse tutorial
Contents:
The argparse module is a function which, when called, creates an instance of the Parser class.
-- script.lua local argparse = require "argparse" local parser = argparse()
parser is now an empty parser which does not recognize any command line arguments or options.
:parse([argv]) method of the Parser class returns a table with processed data from the command line or argv array.
local args = parser:parse()
After this is executed with lua script.lua, args is an empty table because the parser is empty and no command line arguments were supplied.
If the provided command line arguments are not recognized by the parser, it will print an error message and call os.exit(1).
$ lua script.lua foo
Usage: script.lua [-h] Error: too many arguments
If halting the program is undesirable, :pparse([args]) method should be used. It returns boolean flag indicating success of parsing and result or error message.
An error can raised manually using :error() method.
parser:error("manual argument validation failed")
Usage: script.lua [-h] Error: manual argument validation failed
As the automatically generated usage message states, there is a help option -h added to any parser by default.
When a help option is used, parser will print a help message and call os.exit(0).
$ lua script.lua -h
Usage: script.lua [-h] Options:
-h, --help Show this help message and exit.
When an option is not recognized by the parser, but there is an option with a similar name, a suggestion is automatically added to the error message.
$ lua script.lua --hepl
Usage: script.lua [-h] Error: unknown option '--hepl' Did you mean '--help'?
Parsers have several properties affecting their behavior. For example, description and epilog properties set the text to be displayed in the help message after the usage message and after the listings of options and arguments, respectively. Another is name, which overwrites the name of the program which is used in the usage message (default value is inferred from command line arguments).
There are several ways to set properties. The first is to chain setter methods of Parser object.
local parser = argparse()
:name "script"
:description "A testing script."
:epilog "For more info, see http://example.com"
The second is to call a parser with a table containing some properties.
local parser = argparse() {
name = "script",
description = "A testing script.",
epilog "For more info, see http://example.com."
}
Finally, name. description and epilog properties can be passed as arguments when calling a parser.
local parser = argparse("script", "A testing script.", "For more info, see http://example.com.")
Positional arguments can be added using :argument(name, description, default, convert, args) method. It returns an Argument instance, which can be configured in the same way as Parsers. The name property is required.
This and the following examples show contents of the result table returned by parser:parse() when the script is executed with given command-line arguments.
parser:argument "input"
$ lua script.lua foo
{
input = "foo"
}
The data passed to the argument is stored in the result table at index input because it is the argument's name. The index can be changed using target property.
args property sets how many command line arguments the argument consumes. Its value is interpreted as follows:
| Value | Interpretation |
| Number N | Exactly N arguments |
| String A-B, where A and B are numbers | From A to B arguments |
| String N+, where N is a number | N or more arguments |
| String ? | An optional argument |
| String * | Any number of arguments |
| String + | At least one argument |
If more than one argument can be consumed, a table is used to store the data.
parser:argument("pair", "A pair of arguments.")
:args(2)
parser:argument("optional", "An optional argument.")
:args "?"
$ lua script.lua foo bar
{
pair = {"foo", "bar"}
}
$ lua script.lua foo bar baz
{
pair = {"foo", "bar"},
optional = "baz"
}
Options can be added using :option(name, description, default, convert, args, count) method. It returns an Option instance, which can be configured in the same way as Parsers. The name property is required. An option can have several aliases, which can be set as space separated substrings in its name or by continuously setting name property.
-- These lines are equivalent: parser:option "-f" "--from" parser:option "-f --from"
$ lua script.lua --from there $ lua script.lua --from=there $ lua script.lua -f there $ lua script.lua -fthere
{
from = "there"
}
For an option, default index used to store arguments passed to it is the first "long" alias (an alias starting with two control characters, typically hyphens) or just the first alias, without control characters. Hyphens in the default index are replaced with underscores. In the following table it is assumed that local args = parser:parse() has been executed.
| Option's aliases | Location of option's arguments |
| -o | args.o |
| -o --output | args.output |
| -s --from-server | args.from_server |
As with arguments, the index can be explicitly set using target property.
Flags are almost identical to options, except that they don't take an argument by default.
parser:flag("-q --quiet")
$ lua script.lua -q
{
quiet = true
}
The first characters of all aliases of all options of a parser form the set of control characters, used to distinguish options from arguments. Typically the set only consists of a hyphen.
Just as arguments, options can be configured to take several command line arguments.
parser:option "--pair"
:args(2) parser:option "--optional"
:args "?"
$ lua script.lua --pair foo bar
{
pair = {"foo", "bar"}
}
$ lua script.lua --pair foo bar --optional
{
pair = {"foo", "bar"},
optional = {}
}
$ lua script.lua --optional=baz
{
optional = {"baz"}
}
Note that the data passed to optional option is stored in an array. That is necessary to distinguish whether the option was invoked without an argument or it was not invoked at all.
For options, it is possible to control how many times they can be used. argparse uses count property to set how many times an option can be invoked. The value of the property is interpreted in the same way args is.
parser:option("-e --exclude")
:count "*"
$ lua script.lua -eFOO -eBAR
{
exclude = {"FOO", "BAR"}
}
If an option can be used more than once and it can consume more than one argument, the data is stored as an array of invocations, each being an array of arguments.
As a special case, if an option can be used more than once and it consumes no arguments (e.g. it's a flag), than the number of invocations is stored in the associated field of the result table.
parser:flag("-v --verbose", "Sets verbosity level.")
:count "0-2"
:target "verbosity"
$ lua script.lua -vv
{
verbosity = 2
}
A group of arguments and options can be marked as mutually exclusive using :mutex(argument_or_option, ...) method of the Parser class.
parser:mutex(
parser:argument "input"
:args "?",
parser:flag "--process-stdin" ) parser:mutex(
parser:flag "-q --quiet",
parser:flag "-v --verbose" )
If more than one element of a mutually exclusive group is used, an error is raised.
$ lua script.lua -qv
Usage: script.lua ([-q] | [-v]) [-h] ([<input>] | [--process-stdin]) Error: option '-v' can not be used together with option '-q'
$ lua script.lua file --process-stdin
Usage: script.lua ([-q] | [-v]) [-h] ([<input>] | [--process-stdin]) Error: option '--process-stdin' can not be used together with argument 'input'
A command is a subparser invoked when its name is passed as an argument. For example, in git CLI add, commit, push, etc. are commands. Each command has its own set of arguments and options, but inherits options of its parent.
Commands can be added using :command(name, description, epilog) method. Just as options, commands can have several aliases.
parser:command "install i"
If a command it used, true is stored in the corresponding field of the result table.
$ lua script.lua install
{
install = true
}
A typo will result in an appropriate error message.
$ lua script.lua instal
Usage: script.lua [-h] <command> ... Error: unknown command 'instal' Did you mean 'install'?
Use command_target property of the parser to store the name of used command in a field of the result table.
parser:command_target("command")
parser:command("install")
parser:command("remove")
$ lua script.lua install
{
install = true,
command = "install"
}
The Command class is a subclass of the Parser class, so all the Parser's methods for adding elements work on commands, too.
local install = parser:command "install" install:argument "rock" install:option "-f --from"
$ lua script.lua install foo --from=bar
{
install = true,
rock = "foo",
from = "bar"
}
Commands have their own usage and help messages.
$ lua script.lua install
Usage: script.lua install [-f <from>] [-h] <rock> Error: too few arguments
$ lua script.lua install --help
Usage: script.lua install [-f <from>] [-h] <rock> Arguments:
rock Options:
-f <from>, --from <from>
-h, --help Show this help message and exit.
By default, if a parser has commands, using one of them is obligatory.
local parser = argparse() parser:command "install"
$ lua script.lua
Usage: script.lua [-h] <command> ... Error: a command is required
This can be changed using require_command property.
local parser = argparse()
:require_command(false) parser:command "install"
For elements such as arguments and options, if default property is set to a string, its value is stored in case the element was not used (if it's not a string, it'll be used as init property instead, see actions).
parser:option("-o --output", "Output file.", "a.out")
-- Equivalent:
parser:option "-o" "--output"
:description "Output file."
:default "a.out"
$ lua script.lua
{
output = "a.out"
}
The existence of a default value is reflected in help message, unless show_default property is set to false.
$ lua script.lua --help
Usage: script.lua [-o <output>] [-h] Options:
-o <output>, --output <output>
Output file. (default: a.out)
-h, --help Show this help message and exit.
Note that invocation without required arguments is still an error.
$ lua script.lua -o
Usage: script.lua [-o <output>] [-h] Error: too few arguments
defmode property regulates how argparse should use the default value of an element.
By default, or if defmode contains u (for unused), the default value will be automatically passed to the element if it was not invoked at all. It will be passed minimal required of times, so that if the element is allowed to consume no arguments (e.g. using :args "?"), the default value is ignored.
If defmode contains a (for argument), the default value will be automatically passed to the element if not enough arguments were passed, or not enough invocations were made.
Consider the difference:
parser:option "-o"
:default "a.out" parser:option "-p"
:default "password"
:defmode "arg"
$ lua script.lua -h
Usage: script.lua [-o <o>] [-p [<p>]] [-h] Options:
-o <o> default: a.out
-p [<p>] default: password
-h, --help Show this help message and exit.
$ lua script.lua
{
o = "a.out"
}
$ lua script.lua -p
{
o = "a.out",
p = "password"
}
$ lua script.lua -o
Usage: script.lua [-o <o>] [-p [<p>]] [-h] Error: too few arguments
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'
If convert property of an element is an array of functions, they will be used as converters for corresponding arguments in case the element accepts multiple arguments.
parser:option "--line-style"
:args(2)
:convert {string.lower, tonumber}
$ lua script.lua --line-style DASHED 1.5
{
line_style = {"dashed", 1.5}
}
If convert property of an element is a table and doesn't have functions in array part, 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'
argparse uses action callbacks to process invocations of arguments and options. Default actions simply put passed arguments into the result table as a single value or insert into an array depending on number of arguments the option can take and how many times it can be used.
A custom action can be set using action property. An action must be a function. and will be called after each invocation of the option or the argument it is assigned to. Four arguments are passed: result table, target index in that table, an argument or an array of arguments passed by user, and overwrite flag used when an option is invoked too many times.
Converters are applied before actions.
Initial value to be stored at target index in the result table can be set using init property, or also using default property if the value is not a string.
parser:option("--exceptions"):args("*"):action(function(args, _, exceptions)
for _, exception in ipairs(exceptions) do
table.insert(args.exceptions, exception)
end
end):init({"foo", "bar"})
parser:flag("--no-exceptions"):action(function(args)
args.exceptions = {}
end)
$ lua script.lua --exceptions x y --exceptions z t
{
exceptions = {
"foo",
"bar",
"x",
"y",
"z",
"t"
}
}
$ lua script.lua --exceptions x y --no-exceptions
{
exceptions = {}
}
Actions can also be used when a flag needs to print some message and exit without parsing remaining arguments.
parser:flag("-v --version"):action(function()
print("script v1.0.0")
os.exit(0)
end)
$ lua script.lua -v
script v1.0.0
These actions can be referred to by their string names when setting action property:
| Name | Description |
| store | Stores argument or arguments at target index. |
| store_true | Stores true at target index. |
| store_false | Stores false at target index. |
| count | Increments number at target index. |
| append | Appends argument or arguments to table at target index. |
| concat | Appends arguments one by one to table at target index. |
Examples using store_false and concat actions:
parser:flag("--candy")
parser:flag("--no-candy"):target("candy"):action("store_false")
parser:flag("--rain", "Enable rain", false)
parser:option("--exceptions"):args("*"):action("concat"):init({"foo", "bar"})
$ lua script.lua
{
rain = false
}
$ lua script.lua --candy
{
candy = true,
rain = false
}
$ lua script.lua --no-candy --rain
{
candy = false,
rain = true
}
$ lua script.lua --exceptions x y --exceptions z t
{
exceptions = {
"foo",
"bar",
"x",
"y",
"z",
"t"
},
rain = false
}
Actions for parsers and commands are simply callbacks invoked after parsing, with result table and command name as the arguments. Actions for nested commands are called first.
local install = parser:command("install"):action(function(args, name)
print("Running " .. name)
-- Use args here
)
parser:action(function(args)
print("Callbacks are fun!")
end)
$ lua script.lua install
Running install Callbacks are fun!
The usage and help messages of parsers and commands can be generated on demand using :get_usage() and :get_help() methods, and overridden using help and usage properties. When using the autogenerated usage and help messages, there are several ways to adjust them.
If hidden property for an argument, an option or a command is set to true, it is not included into help and usage messages, but otherwise works normally.
parser:option "--normal-option" parser:option "--deprecated-option"
:hidden(true)
$ lua script.lua --help
Usage: script.lua [--normal-option <normal_option>] [-h] Options:
--normal-option <normal_option>
-h, --help Show this help message and exit.
$ lua script.lua --deprecated-option value
{
deprecated_option = "value"
}
For options and arguments, argname property controls the placeholder for the argument in the usage message.
parser:option "-f" "--from"
:argname "<server>"
$ lua script.lua --help
Usage: script.lua [-f <server>] [-h] Options:
-f <server>, --from <server>
-h, --help Show this help message and exit.
argname can be an array of placeholders.
parser:option "--pair"
:args(2)
:argname {"<key>", "<value>"}
$ lua script.lua --help
Usage: script.lua [--pair <key> <value>] [-h] Options:
--pair <key> <value>
-h, --help Show this help message and exit.
:group(name, ...) method of parsers and commands puts passed arguments, options, and commands into a named group with its own section in the help message. Elements outside any groups are put into a default section.
parser:group("Configuring output format",
parser:flag "-v --verbose",
parser:flag "--use-colors",
parser:option "--encoding"
)
parser:group("Configuring processing",
parser:option "--compression-level",
parser:flag "--skip-broken-chunks"
)
parser:flag "--version"
:action(function() print("script.lua 1.0.0") os.exit(0) end)
$ lua script.lua --help
Usage: script.lua [-v] [--use-colors] [--encoding <encoding>]
[--compression-level <compression_level>]
[--skip-broken-chunks] [--version] [-h] Configuring output format:
-v, --verbose
--use-colors
--encoding <encoding> Configuring processing:
--compression-level <compression_level>
--skip-broken-chunks Other options:
--version
-h, --help Show this help message and exit.
If help_max_width property of a parser or a command is set, when generating its help message, argparse will automatically wrap lines, attempting to fit into given number of columns. This includes wrapping lines in parser description and epilog and descriptions of arguments, options, and commands.
Line wrapping preserves existing line endings and only splits overly long input lines. When breaking a long line, it replicates indentation of the line in the continuation lines. Additionally, if the first non-space token in a line is *, +, or -, the line is considered a list item, and the continuation lines are aligned with the first word after the list item marker.
parser:help_max_width(80) parser:option "-f --foo"
:description("Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor " ..
"incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation " ..
"ullamco laboris nisi ut aliquip ex ea commodo consequat.\n" ..
"The next paragraph is indented:\n" ..
" Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. " ..
"Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.") parser:option "-b --bar"
:description("Here is a list:\n"..
"* Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor...\n" ..
"* Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip...\n" ..
"* Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur.")
$ lua script.lua --help
Usage: script.lua [-f <foo>] [-b <bar>] [-h] Options:
-f <foo>, Lorem ipsum dolor sit amet, consectetur adipiscing
--foo <foo> elit, sed do eiusmod tempor incididunt ut labore et
dolore magna aliqua. Ut enim ad minim veniam, quis
nostrud exercitation ullamco laboris nisi ut aliquip ex
ea commodo consequat.
The next paragraph is indented:
Duis aute irure dolor in reprehenderit in voluptate
velit esse cillum dolore eu fugiat nulla pariatur.
Excepteur sint occaecat cupidatat non proident, sunt
in culpa qui officia deserunt mollit anim id est
laborum.
-b <bar>, Here is a list:
--bar <bar> * Lorem ipsum dolor sit amet, consectetur adipiscing
elit, sed do eiusmod tempor...
* Ut enim ad minim veniam, quis nostrud exercitation
ullamco laboris nisi ut aliquip...
* Duis aute irure dolor in reprehenderit in voluptate
velit esse cillum dolore eu fugiat nulla pariatur.
-h, --help Show this help message and exit.
help_max_width property is inherited by commands.
Several other parser and command properties can be used to tweak help and usage message format. Like help_max_width, all of them are inherited by commands when set on the parser or a parent command.
usage_max_width property sets maximum width of the usage string. Default is 70.
usage_margin property sets margin width used when line wrapping long usage strings. Default is 7.
parser:usage_max_width(50)
:usage_margin(#"Usage: script.lua ") parser:option "--foo" parser:option "--bar" parser:option "--baz" parser:option "--qux" print(parser:get_usage())
$ lua script.lua
Usage: script.lua [--foo <foo>] [--bar <bar>]
[--baz <baz>] [--qux <qux>] [-h]
Help message for a group of arguments, options, or commands is organized into two columns, with usage template on the left side and descriptions on the right side. help_usage_margin property sets horizontal offset for the first column (3 by default). help_description_margin property sets horizontal offset for the second column (25 by default).
help_vertical_space property sets number of extra empty lines to put between descriptions for different elements within a group (0 by default).
parser:help_usage_margin(2)
:help_description_margin(17)
:help_vertical_space(1) parser:option("--foo", "Set foo.") parser:option("--bar", "Set bar.") parser:option("--baz", "Set baz.") parser:option("--qux", "Set qux.")
$ lua script.lua --help
Usage: script.lua [--foo <foo>] [--bar <bar>] [--baz <baz>]
[--qux <qux>] [-h] Options:
--foo <foo> Set foo.
--bar <bar> Set bar.
--baz <baz> Set baz.
--qux <qux> Set qux.
-h, --help Show this help message and exit.
argparse module is a table with __call metamethod. argparse.version is a string in MAJOR.MINOR.PATCH format specifying argparse version.
If the property add_help of a parser is set to false, no help option will be added to it. Otherwise, the value of the field will be used to configure it.
local parser = argparse()
:add_help "/?"
$ lua script.lua /?
Usage: script.lua [/?] Options:
/? Show this help message and exit.
When handle_options property of a parser or a command is set to false, all options will be passed verbatim to the argument list, as if the input included double-hyphens.
parser:handle_options(false) parser:argument "input"
:args "*" parser:option "-f" "--foo"
:args "*"
$ lua script.lua bar -f --foo bar
{
input = {"bar", "-f", "--foo", "bar"}
}
By default, if an option is invoked too many times, latest invocations overwrite the data passed earlier.
parser:option "-o --output"
$ lua script.lua -oFOO -oBAR
{
output = "BAR"
}
Set overwrite property to false to prohibit this behavior.
parser:option "-o --output"
:overwrite(false)
$ lua script.lua -oFOO -oBAR
Usage: script.lua [-o <output>] [-h] Error: option '-o' must be used at most 1 time
argparse interprets command line arguments in the following way:
| Argument | Interpretation |
| foo | An argument of an option or a positional argument. |
| --foo | An option. |
| --foo=bar | An option and its argument. The option must be able to take arguments. |
| -f | An option. |
| -abcdef | Letters are interpreted as options. If one of them can take an argument, the rest of the string is passed to it. |
| -- | The rest of the command line arguments will be interpreted as positional arguments. |
Properties that can be set as arguments when calling or constructing a parser, in this order:
| Property | Type |
| name | String |
| description | String |
| epilog | String |
Other properties:
| Property | Type |
| usage | String |
| help | String |
| require_command | Boolean |
| handle_options | Boolean |
| add_help | Boolean or string or table |
| command_target | String |
| usage_max_width | Number |
| usage_margin | Number |
| help_max_width | Number |
| help_usage_margin | Number |
| help_description_margin | Number |
| help_vertical_space | Number |
Properties that can be set as arguments when calling or constructing a command, in this order:
| Property | Type |
| name | String |
| description | String |
| epilog | String |
Other properties:
| Property | Type |
| target | String |
| usage | String |
| help | String |
| require_command | Boolean |
| handle_options | Boolean |
| action | Function |
| add_help | Boolean or string or table |
| command_target | String |
| hidden | Boolean |
| usage_max_width | Number |
| usage_margin | Number |
| help_max_width | Number |
| help_usage_margin | Number |
| help_description_margin | Number |
| help_vertical_space | Number |
Properties that can be set as arguments when calling or constructing an argument, in this order:
| Property | Type |
| name | String |
| description | String |
| default | Any |
| convert | Function or table |
| args | Number or string |
Other properties:
| Property | Type |
| target | String |
| defmode | String |
| show_default | Boolean |
| argname | String or table |
| action | Function or string |
| init | Any |
| hidden | Boolean |
Properties that can be set as arguments when calling or constructing an option or a flag, in this order:
| Property | Type |
| name | String |
| description | String |
| default | Any |
| convert | Function or table |
| args | Number or string |
| count | Number or string |
Other properties:
| Property | Type |
| target | String |
| defmode | String |
| show_default | Boolean |
| overwrite | Booleans |
| argname | String or table |
| action | Function or string |
| init | Any |
| hidden | Boolean |
This is a tutorial for argparse, a feature-rich command line parser for Lua.
Peter Melnichenko
2021 - 2018, Peter Melnichenko
| January 3, 2021 | 0.6.0 |