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README
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This is a library for parsing command-line arguments. It can parse both options and positional arguments. It aims to be easy to use and concise yet powerful and robust.
Overview
Defining options and positional arguments is as simple as:
import com.xenomachina.argparser.ArgParser
class MyArgs(parser: ArgParser) {
val v by parser.flagging("enable verbose mode")
val name by parser.storing("name of the user")
val count by parser.storing("number of the widgets") { toInt() }
val source by parser.positional("source filename")
val destination by parser.positional("destination filename")
}
An instance of MyArgs
will represent the set of parsed arguments. Each option
and positional argument is declared as a property that delegates through a
delegate factory method on an instance of ArgParser
.
The name of an option is inferred from the name of the property it is bound to.
The options above are named -v
, --name
and --count
, respectively. There
are also two positional arguments.
Direct control over an option's name is also possible, and for most types of options it is also possible to have multiple names, like a short and long name:
class MyArgs(parser: ArgParser) {
val verbose by parser.flagging(
"-v", "--verbose",
help = "enable verbose mode")
val name by parser.storing(
"-N", "--name",
help = "name of the user")
val count by parser.storing(
"-c", "--count",
help = "number of widgets") { toInt() }
val source by parser.positional(
"SOURCE",
help = "source filename")
val destination by parser.positional(
"DEST",
help = "destination filename")
}
The unparsed command-line arguments are passed to the ArgParser
instance at
construction:
fun main(args: Array<String>) = mainBody {
ArgParser(args).parseInto(::MyArgs).run {
println("Hello, ${name}!")
println("I'm going to move ${count} widgets from ${source} to ${destination}.")
// TODO: move widgets
}
}
See kotlin-argparser-example for a complete example project.
Nomenclature
Options, arguments, flags... what's the difference?
An application's main
function is passed an array of strings. These are
the unparsed command-line arguments, or unparsed arguments for short.
The unparsed arguments can then be parsed into options, which start
with a hyphen ("-
"), and positional arguments. For example, in the command
ls -l /tmp/
, the unparsed arguments would be "-l", "/tmp"
where -l
is an option, while /tmp/
is a positional argument.
Options can also have option arguments. In the command ls --time-style=iso
,
the option is --time-style
and that options argument is iso
. Note that in
parsing a single unparsed argument can be split into an option and an option
argument, or even into multiple options in some cases.
A flag is a boolean option which has no arguments and which is false if not
provided, but true if provided. The -l
option of ls
is a flag.
Option Types
Boolean Flags
Boolean flags are created by asking the parser for a flagging
delegate. One
or more option names, may be provided:
val verbose by parser.flagging("-v", "--verbose",
help = "enable verbose mode")
Here the presence of either -v
or --verbose
options in the
arguments will cause the Boolean
property verbose
to be true
, otherwise
it will be false
.
Storing a Single Argument
Single argument options are created by asking the parser for a
storing
delegate.
val name by parser.storing("-N", "--name",
help = "name of the user")
Here either -N
or --name
with an argument will cause the name
property to
have that argument as its value.
A function can also be supplied to transform the argument into the desired
type. Here the size
property will be an Int
rather than a String
:
val size by parser.storing("-c", "--count",
help = "number of widgets") { toInt() }
Adding to a Collection
Options that add to a Collection
each time they appear in the arguments are
created with using the adding
delegate. Just like storing
delegates, a
transform function may optionally be supplied:
val includeDirs by parser.adding(
"-I", help = "directory to search for header files") { File(this) }
Now each time the -I
option appears, its transformed argument is appended to
includeDirs
.
Mapping from an option to a fixed value
For choosing between a fixed set of values (typically, but not necessarily,
from an enum), a mapping
delegate can be used:
val mode by parser.mapping(
"--fast" to Mode.FAST,
"--small" to Mode.SMALL,
"--quiet" to Mode.QUIET,
help = "mode of operation")
Here the mode
property will be set to the corresponding ArgParser.Mode
value depending
on which of --fast
, --small
, and --quiet
appears (last) in the arguments.
mapping
is one of the few cases where it is not possible to infer the option
name from the property name.
More advanced options
For all other types of options, the option
method should be used. The
methods mentioned above are, in fact, convenience methods built on top of the
option
method.
For example, it is possible to create an option that has multiple arguments:
fun ArgParser.putting(vararg names: String, help: String) =
option<MutableMap<String, String>>(*names,
argNames = listOf("KEY", "VALUE"),
help = help) {
value.orElse { mutableMapOf<String, String>() }.apply {
put(arguments.first(), arguments.last()) }
}
Note that the option
method does not have an auto-naming overload. If you
need this capability, create a DelegateProvider
that creates your Delegate
:
fun ArgParser.putting(help: String) =
ArgParser.DelegateProvider { identifier ->
putting(identifierToOptionName(identifier), help = help) }
Positional Arguments
Positional arguments are collected by using the positional
and
positionalList
methods.
For a single positional argument:
val destination by parser.positional("destination filename")
An explicit name may also be specified:
val destination by parser.positional("DEST",
help = "destination filename")
The name ("DEST", here) is used in error handling and help text.
For a list of positional arguments:
val sources by parser.positionalList("SOURCE", 1..Int.MAX_VALUE,
help = "source filename")
The range indicates how many arguments should be collected, and defaults to the
value shown in this example. As the name suggests, the resulting property will
be a List
.
Both of these methods accept an optional transform function for converting
arguments from String
to whatever type is actually desired:
val destination by parser.positional("DEST",
help = "...") { File(this) }
val sources by parser.positionalList("SOURCE", 1..Int.MAX_VALUE,
help = "...") { File(this) }
Modifying Delegates
The delegates returned by any of these methods also have a few methods for setting optional attributes:
Adding a Default Value
Certain types of delegates (notably storing
, mapping
, and positional
)
have no default value, and hence will be required options unless a default
value is provided. This is done with the default
method:
val name by parser.storing("-N", "--name", help = "...").default("John Doe")
Note that it is possible to use null
for the default, though this may
require specifying the type parameter for default
explicitly:
val name by parser.storing("-N", "--name", help = "...").default<String?>(null)
The type of the resulting property be nullable (a String?
in this case).
Adding a Validator
Sometimes it's easier to validate an option at the end of parsing, in which
case the addValidator
method can be used.
val percentages by parser.adding("--percentages", help = "...") { toInt() }
.addValidator {
if (value.sum() != 100)
throw InvalidArgumentException(
"Percentages must add up to 100%")
}
Error Handling
If the parser determines that execution should not continue it will throw a
SystemExitException
which has a status code appropriate for passing to
exitProcess
as well as a message for the user.
These exceptions can be caused by user error, or even if the user requests help
(eg: via the --help
option).
It is recommended that transform functions (given to storing
,
positionalList
, etc.) and post-parsing validation, including that performed
via, addValidator
also throw a SystemExitException
on failure.
As a convenience, these exceptions can be handled by using the mainBody
function:
class ParsedArgs(parser: ArgParser) {
val name by positional("The user's name").default("world")
}
fun main(args: Array<String>) = mainBody {
ArgParser(args).parseInto(::ParsedArgs).run {
println("Hello, {name}!")
}
}
Parsing
Parsing of command-line arguments is performed sequentially. So long as
option-processing is enabled, each not-yet-processed command-line argument that
starts with a hyphen (-
) is treated as an option.
Short Options
Short options start with a single hyphen. If the option takes an argument, the argument can either be appended:
# "-o" with argument "ARGUMENT"
my_program -oARGUMENT
or can be the following command-line argument:
# "-o" with argument "ARGUMENT"
my_program -o ARGUMENT
Zero argument short options can also be appended to each other without intermediate hyphens:
# "-x", "-y" and "-z" options
my_program -xyz
An option that accepts arguments is also allowed at the end of such a chain:
# "-x", "-y" and "-z" options, with argument for "-z"
my_program -xyzARGUMENT
Long Options
Long options start with a double hyphen (--
). An argument to a long option
can
either be delimited with an equal sign (=
):
# "--foo" with argument "ARGUMENT"
my_program --foo=ARGUMENT
or can be the following command-line argument:
# "--foo" with argument "ARGUMENT"
my_program --foo ARGUMENT
Multi-argument Options
Multi-argument options are supported, though currently not by any of the convenience methods. Option-arguments after the first must be separate command-line arguments, for both an long and short forms of an option.
Positional Arguments
In GNU mode (the default), options can be interspersed with positional arguments, but in POSIX mode the first positional argument that is encountered disables option processing for the remaining arguments. In either mode, if the argument "--" is encountered while option processing is enabled, then option processing is disabled for the rest of the command-line. Once the options and option-arguments have been eliminated, what remains are considered to be positional arguments.
Each positional argument delegate can specify a minimum and maximum number of arguments it is willing to collect.
The positional arguments are distributed to the delegates by allocating each positional delegate at least as many arguments as it requires. If more than the minimum number of positional arguments have been supplied then additional arguments will be allocated to the first delegate up to its maximum, then the second, and so on, until all arguments have been allocated to a delegate.
This makes it easy to create a program that behaves like grep
:
class Args(parser: ArgParser) {
// accept 1 regex followed by n filenames
val regex by parser.positional("REGEX",
help = "regular expression to search for")
val files by parser.positionalList("FILE",
help = "file to search in")
}
And equally easy to create a program that behaves like cp
:
class Args(parser: ArgParser) {
// accept n source files followed by 1 destination
val sources by parser.positionalList("SOURCE",
help = "source file")
val destination by parser.positional("DEST",
help = "destination file")
}
Forcing Parsing
Parsing normally does not begin until a delegate's value is accessed. Sometimes this is not desirable, so it is possible to enforce the parsing of arguments into a class of values. This ensures that all arguments that are required are provided, and all arguments provided are consumed.
Forcing can be done in a separate step using the force
method:
val parser = ArgParser(args)
val parsedArgs = ParsedArgs(parser)
parser.force()
// now you can use parsedArgs
Alternatively, forcing can be done inline via the parseInto
method:
val parsedArgs = ArgParser(args).parseInto(::ParsedArgs)
// now you can use parsedArgs
In both cases exceptions will be thrown where parsing or validation errors are found.
Help Formatting
By default, ArgParser
will add a --help
option (short name -h
) for
displaying usage information. If this option is present a ShowHelpException
will be thrown.
If the default exception handling is being used (see Error Handling) the
program will halt and print a help message like the one below, based on the ArgParser
configuration:
usage: program_name [-h] [-n] [-I INCLUDE]... -o OUTPUT
[-v]... SOURCE... DEST
This is the prologue. Lorem ipsum dolor sit amet, consectetur
adipiscing elit. Aliquam malesuada maximus eros. Fusce
luctus risus eget quam consectetur, eu auctor est
ullamcorper. Maecenas eget suscipit dui, sed sodales erat.
Phasellus.
required arguments:
-o OUTPUT, directory in which all output should
--output OUTPUT be generated
optional arguments:
-h, --help show this help message and exit
-n, --dry-run don't do anything
-I INCLUDE, search in this directory for header
--include INCLUDE files
-v, --verbose increase verbosity
positional arguments:
SOURCE source file
DEST destination file
This is the epilogue. Lorem ipsum dolor sit amet,
consectetur adipiscing elit. Donec vel tortor nunc. Sed eu
massa sed turpis auctor faucibus. Donec vel pellentesque
tortor. Ut ultrices tempus lectus fermentum vestibulum.
Phasellus.
The creation of the --help
option can be disabled by passing null
as the
helpFormatter
when constructing the ArgParser
, or configured by manually
constructing a HelpFormatter
instance. In the above example a
DefaultHelpFormatter
was created with the prologue and epilogue.
Caveats
This library should be considered to be very beta. While there are no plans to make any breaking changes to the API, it's possible that there may be some until it is mature.
Upon reading the value any of the delegated properties created by an
ArgParser
, the arguments used to construct thatArgParser
will be parsed. This means it's important that you don't attempt to create delegates on anArgParser
after any of its existing delegated properties have been read. Attempting to do so will cause anIllegalStateException
. It would be nice if Kotlin had facilities for doing some of the work ofArgParser
at compile time rather than run time, but so far the run time errors seem to be reasonably easy to avoid.
Configuring Your Build
<!-- TODO move detailed instructions elsewhere, just have brief instructions here -->
Kotlin-argparser binaries are hosted on Maven Central and also Bintray's JCenter.
In Gradle, add something like this in your build.gradle
:
// you probably already have this part
buildscript {
repositories {
mavenCentral() // or jcenter()
}
}
dependencies {
compile "com.xenomachina:kotlin-argparser:$kotlin_argparser_version"
}
In Maven add something like this to your pom.xml
:
<dependency>
<groupId>com.xenomachina</groupId>
<artifactId>kotlin-argparser</artifactId>
<version>VERSION</version>
</dependency>
Information on setting up other build systems, as well as the current version number, can be found on MVN Repository's page for Kotlin-argparser.
Thanks
Thanks to the creators of Python's
argparse
module, which
provided the initial inspiration for this library.
Thanks also to the team behind Kotlin.
Finally, thanks to all of the people who have contributed code and/or issues.
*Note that all licence references and agreements mentioned in the kotlin-argparser README section above
are relevant to that project's source code only.