[−][src]Crate structopt
This crate defines the StructOpt
trait and its custom derive.
Features
If you want to disable all the clap
features (colors,
suggestions, ..) add default-features = false
to the structopt
dependency:
[dependencies]
structopt = { version = "0.2", default-features = false }
Support for paw
(the
Command line argument paw-rser abstraction for main
) is disabled
by default, but can be enabled in the structopt
dependency
with the feature paw
:
[dependencies]
structopt = { version = "0.2", features = [ "paw" ] }
paw = "1.0"
How to derive(StructOpt)
First, let's look at the example:
use std::path::PathBuf; use structopt::StructOpt; #[derive(Debug, StructOpt)] #[structopt(name = "example", about = "An example of StructOpt usage.")] struct Opt { /// Activate debug mode // short and long flags (-d, --debug) will be deduced from the field's name #[structopt(short, long)] debug: bool, /// Set speed // we don't want to name it "speed", need to look smart #[structopt(short = "v", long = "velocity", default_value = "42")] speed: f64, /// Input file #[structopt(parse(from_os_str))] input: PathBuf, /// Output file, stdout if not present #[structopt(parse(from_os_str))] output: Option<PathBuf>, /// Where to write the output: to `stdout` or `file` #[structopt(short)] out_type: String, /// File name: only required when `out` is set to `file` #[structopt(name = "FILE", required_if("out_type", "file"))] file_name: String, } fn main() { let opt = Opt::from_args(); println!("{:?}", opt); }
So derive(StructOpt)
tells Rust to generate a command line parser,
and the various structopt
attributes are simply
used for additional parameters.
First, define a struct, whatever its name. This structure
corresponds to a clap::App
, its fields correspond to clap::Arg
(unless they're subcommands),
and you can adjust these apps and args by #[structopt(...)]
attributes.
Attributes
#[structopt(...)]
attributes fall into two categories:
-
structopt
's own magical methods.They are used by
structopt
itself. They come mostly inattr = ["whatever"]
form, but someattr(args...)
also exist. -
They represent explicit
clap::Arg/App
method calls. They are what used to be explicit#[structopt(raw(...))]
attrs in pre-0.3structopt
Every structopt attribute
looks like comma-separated sequence of methods:
#[structopt(
short, // method with no arguments - always magical
long = "--long-option", // method with one argument
required_if("out", "file"), // method with one and more args
parse(from_os_str = path::to::parser) // some magical methods have their own syntax
)]
#[structopt(...)]
attributes can be placed on top of struct
, enum
,
struct
field or enum
variant. Attributes on top of struct
or enum
represent clap::App
method calls, field or variant attributes correspond
to clap::Arg
method calls.
In other words, the Opt
struct from the example above
will be turned into this (details omitted):
App::new("example") .version("0.2.0") .about("An example of StructOpt usage.") .arg(Arg::with_name("debug") .help("Activate debug mode") .short("debug") .long("debug")) .arg(Arg::with_name("speed") .help("Set speed") .short("s") .long("speed") .default_value("42")) // and so on
Raw methods
They are the reason why structopt
is so flexible.
Each and every method from clap::App
and clap::Arg
can be used directly -
just #[structopt(method_name = single_arg)]
or #[structopt(method_name(arg1, arg2))]
and it just works. As long as method_name
is not one of the magical methods -
it's just a method call.
Note: the Arg::raw
method is allowed only with true
or false
literals.
Magical methods
They are the reason why structopt
is so easy to use and convenient in most cases.
Many of them have defaults, some of them get used even if not mentioned.
Methods may be used on "top level" (on top of a struct
, enum
or enum
variant)
and/or on "field-level" (on top of a struct
field or inside of an enum variant).
Top level (non-magical) methods correspond to App::method
calls, field-level methods
are Arg::method
calls.
#[structopt(top_level)] struct Foo { #[structopt(field_level)] field: u32 } #[structopt(top_level)] enum Bar { #[structopt(top_level)] Pineapple { #[structopt(field_level)] chocolate: String }, #[structopt(top_level)] Orange, }
-
name
:[name = "name"]
-
On top level:
App::new("name")
.The binary name displayed in help messages. Defaults to the crate name given by Cargo.
-
On field-level:
Arg::with_name("name")
.The name for the argument the field stands for, this name appears in help messages. Defaults to a name, deduced from a field, see also
rename_all
.
-
-
version
:[version = "version"]
Usable only on top level:
App::version("version" or env!(CARGO_PKG_VERSION))
.The version displayed in help messages. Defaults to the crate version given by Cargo. If
CARGO_PKG_VERSION
is not set no.version()
calls will be generated unless requested. -
no_version
:no_version
Usable only on top level. Prevents default
App::version
call, i.e when noversion = "version"
mentioned. -
author
:author [= "author"]
Usable only on top level:
App::author("author" or env!(CARGO_PKG_AUTHOR))
.Author/maintainer of the binary, this name appears in help messages. Defaults to the crate author given by cargo, but only when
author
explicitly mentioned. -
about
:about [= "about"]
Usable only on top level:
App::about("about" or env!(CARGO_PKG_DESCRIPTION))
.Short description of the binary, appears in help messages. Defaults to the crate description given by cargo, but only when
about
explicitly mentioned. -
short
:short [= "short-opt-name"]
Usable only on field-level.
-
long
:long [= "long-opt-name"]
Usable only on field-level.
-
rename_all
: [rename_all = "kebab"/"snake"/"screaming-snake"/"camel"/"pascal"/"verbatim"]
Usable only on top level
-
parse
:parse(type [= path::to::parser::fn])
Usable only on field-level.
-
skip
:skip
Usable only on field-level.
-
flatten
:flatten
Usable only on field-level.
-
subcommand
:subcommand
Usable only on field-level.
Type magic
One of major things that makes structopt
so awesome is it's type magic.
Do you want optional positional argument? Use Option<T>
! Or perhaps optional argument
that optionally takes value ([--opt=[val]]
)? Use Option<Option<T>>
!
Here is the table of types and clap
methods they correspond to:
Type | Effect | Added method call to clap::Arg |
---|---|---|
bool | true if the flag is present | .takes_value(false).multiple(false) |
Option<T: FromStr> | optional positional argument or option | .takes_value(true).multiple(false) |
Option<Option<T: FromStr>> | optional option with optional value | .takes_value(true).multiple(false).min_values(0).max_values(1) |
Vec<T: FromStr> | list of options or the other positional arguments | .takes_value(true).multiple(true) |
Option<Vec<T: FromStr> | optional list of options | .takes_values(true).multiple(true).min_values(0) |
T: FromStr | required option or positional argument | .takes_value(true).multiple(false).required(!has_default) |
The FromStr
trait is used to convert the argument to the given
type, and the Arg::validator
method is set to a method using
to_string()
(FromStr::Err
must implement std::fmt::Display
).
If you would like to use a custom string parser other than FromStr
, see
the same titled section below.
Thus, the speed
argument is generated as:
clap::Arg::with_name("speed") .takes_value(true) .multiple(false) .required(false) .validator(parse_validator::<f64>) .short("s") .long("speed") .help("Set speed") .default_value("42");
Specifying argument types
There are three types of arguments that can be supplied to each (sub-)command:
- short (e.g.
-h
), - long (e.g.
--help
) - and positional.
Like clap, structopt defaults to creating positional arguments.
If you want to generate a long argument you can specify either
long = $NAME
, or just long
to get a long flag generated using
the field name. The generated casing style can be modified using
the rename_all
attribute. See the rename_all
example for more.
For short arguments, short
will use the first letter of the
field name by default, but just like the long option it's also
possible to use a custom letter through short = $LETTER
.
If an argument is renamed using name = $NAME
any following call to
short
or long
will use the new name.
Attention: If these arguments are used without an explicit name
the resulting flag is going to be renamed using kebab-case
if the
rename_all
attribute was not specified previously. The same is true
for subcommands with implicit naming through the related data structure.
use structopt::StructOpt; #[derive(StructOpt)] #[structopt(rename_all = "kebab-case")] struct Opt { /// This option can be specified with something like `--foo-option /// value` or `--foo-option=value` #[structopt(long)] foo_option: String, /// This option can be specified with something like `-b value` (but /// not `--bar-option value`). #[structopt(short)] bar_option: String, /// This option can be specified either `--baz value` or `-z value`. #[structopt(short = "z", long = "baz")] baz_option: String, /// This option can be specified either by `--custom value` or /// `-c value`. #[structopt(name = "custom", long, short)] custom_option: String, /// This option is positional, meaning it is the first unadorned string /// you provide (multiple others could follow). my_positional: String, /// This option is skipped and will be filled with the default value /// for its type (in this case 0). #[structopt(skip)] skipped: u32, }
Help messages
Help messages for the whole binary or individual arguments can be
specified using the about
attribute on the struct and the help
attribute on the field, as we've already seen. For convenience,
they can also be specified using doc comments. For example:
#[derive(StructOpt)] /// The help message that will be displayed when passing `--help`. struct Foo { #[structopt(short)] /// The description for the arg that will be displayed when passing `--help`. bar: String }
If it is necessary or wanted to provide a more complex help message then the
previous used ones, it could still be a good idea to distinguish between the
actual help message a short summary. In this case about
and help
should
only contain the short and concise form while the two additional arguments
long_about
and long_help
can be used to store a descriptive and more in
depth message.
If both - the short and the long version of the argument - are present,
the user can later chose between the short summary (-h
) and the long
descriptive version (--help
) of the help message. Also in case
of subcommands the short help message will automatically be used for the
command description inside the parents help message and the long version
as command description if help is requested on the actual subcommand.
This feature can also be used with doc comments instead of arguments through proper comment formatting. To be activated it requires, that the first line of the comment is separated from the rest of the comment through an empty line. In this case the first line is used as summary and the whole comment represents the long descriptive message.
#[derive(StructOpt)] /// The help message that will be displayed when passing `--help`. struct Foo { #[structopt(short)] /// Only this summary is visible when passing `-h`. /// /// But the whole comment will be displayed when passing `--help`. /// This could be quite useful to provide further hints are usage /// examples. bar: String }
Environment Variable Fallback
It is possible to specify an environment variable fallback option for an arguments so that its value is taken from the specified environment variable if not given through the command-line:
#[derive(StructOpt)] struct Foo { #[structopt(short, long, env = "PARAMETER_VALUE")] param: String }
By default, values from the environment are shown in the help output (i.e. when invoking
--help
):
$ cargo run -- --help
...
OPTIONS:
-p, --param <param> [env: PARAMETER_VALUE=env_value]
In some cases this may be undesirable, for example when being used for passing
credentials or secret tokens. In those cases you can use hide_env_values
to avoid
having strucopt emit the actual secret values:
#[derive(StructOpt)] struct Foo { #[structopt(long = "secret", env = "SECRET_VALUE", hide_env_values = true)] param: String }
Skipping fields
Sometimes you may want to add a field to your Opt
struct that is not
a command line option and clap
should know nothing about it. You can ask
structopt
to skip the field entirely via #[structopt(skip)]
. Note that
the field type has to implement std::default::Default
then.
Subcommands
Some applications, especially large ones, split their functionality
through the use of "subcommands". Each of these act somewhat like a separate
command, but is part of the larger group.
One example is git
, which has subcommands such as add
, commit
,
and clone
, to mention just a few.
clap
has this functionality, and structopt
supports it through enums:
#[derive(StructOpt)] #[structopt(about = "the stupid content tracker")] enum Git { Add { #[structopt(short)] interactive: bool, #[structopt(short)] patch: bool, #[structopt(parse(from_os_str))] files: Vec<PathBuf> }, Fetch { #[structopt(long)] dry_run: bool, #[structopt(long)] all: bool, repository: Option<String> }, Commit { #[structopt(short)] message: Option<String>, #[structopt(short)] all: bool } }
Using derive(StructOpt)
on an enum instead of a struct will produce
a clap::App
that only takes subcommands. So git add
, git fetch
,
and git commit
would be commands allowed for the above example.
structopt
also provides support for applications where certain flags
need to apply to all subcommands, as well as nested subcommands:
#[derive(StructOpt)] struct MakeCookie { #[structopt(name = "supervisor", default_value = "Puck", long = "supervisor")] supervising_faerie: String, /// The faerie tree this cookie is being made in. tree: Option<String>, #[structopt(subcommand)] // Note that we mark a field as a subcommand cmd: Command } #[derive(StructOpt)] enum Command { /// Pound acorns into flour for cookie dough. Pound { acorns: u32 }, /// Add magical sparkles -- the secret ingredient! Sparkle { #[structopt(short, parse(from_occurrences))] magicality: u64, #[structopt(short)] color: String }, Finish(Finish), } // Subcommand can also be externalized by using a 1-uple enum variant #[derive(StructOpt)] struct Finish { #[structopt(short)] time: u32, #[structopt(subcommand)] // Note that we mark a field as a subcommand finish_type: FinishType } // subsubcommand! #[derive(StructOpt)] enum FinishType { Glaze { applications: u32 }, Powder { flavor: String, dips: u32 } }
Marking a field with structopt(subcommand)
will add the subcommands of the
designated enum to the current clap::App
. The designated enum must also
be derived StructOpt
. So the above example would take the following
commands:
make-cookie pound 50
make-cookie sparkle -mmm --color "green"
make-cookie finish 130 glaze 3
Optional subcommands
A nested subcommand can be marked optional:
#[derive(StructOpt)] struct Foo { file: String, #[structopt(subcommand)] cmd: Option<Command> } #[derive(StructOpt)] enum Command { Bar, Baz, Quux }
Flattening
It can sometimes be useful to group related arguments in a substruct,
while keeping the command-line interface flat. In these cases you can mark
a field as flatten
and give it another type that derives StructOpt
:
#[derive(StructOpt)] struct Cmdline { /// switch on verbosity #[structopt(short)] verbose: bool, #[structopt(flatten)] daemon_opts: DaemonOpts, } #[derive(StructOpt)] struct DaemonOpts { /// daemon user #[structopt(short)] user: String, /// daemon group #[structopt(short)] group: String, }
In this example, the derived Cmdline
parser will support the options -v
,
-u
and -g
.
This feature also makes it possible to define a StructOpt
struct in a
library, parse the corresponding arguments in the main argument parser, and
pass off this struct to a handler provided by that library.
Custom string parsers
If the field type does not have a FromStr
implementation, or you would
like to provide a custom parsing scheme other than FromStr
, you may
provide a custom string parser using parse(...)
like this:
use std::num::ParseIntError; use std::path::PathBuf; fn parse_hex(src: &str) -> Result<u32, ParseIntError> { u32::from_str_radix(src, 16) } #[derive(StructOpt)] struct HexReader { #[structopt(short, parse(try_from_str = parse_hex))] number: u32, #[structopt(short, parse(from_os_str))] output: PathBuf, }
There are five kinds of custom parsers:
Kind | Signature | Default |
---|---|---|
from_str | fn(&str) -> T | ::std::convert::From::from |
try_from_str | fn(&str) -> Result<T, E> | ::std::str::FromStr::from_str |
from_os_str | fn(&OsStr) -> T | ::std::convert::From::from |
try_from_os_str | fn(&OsStr) -> Result<T, OsString> | (no default function) |
from_occurrences | fn(u64) -> T | value as T |
The from_occurrences
parser is special. Using parse(from_occurrences)
results in the number of flags occurrences being stored in the relevant
field or being passed to the supplied function. In other words, it converts
something like -vvv
to 3
. This is equivalent to
.takes_value(false).multiple(true)
. Note that the default parser can only
be used with fields of integer types (u8
, usize
, i64
, etc.).
When supplying a custom string parser, bool
will not be treated specially:
Type | Effect | Added method call to clap::Arg |
---|---|---|
Option<T> | optional argument | .takes_value(true).multiple(false) |
Vec<T> | list of arguments | .takes_value(true).multiple(true) |
T | required argument | .takes_value(true).multiple(false).required(!has_default) |
In the try_from_*
variants, the function will run twice on valid input:
once to validate, and once to parse. Hence, make sure the function is
side-effect-free.
Re-exports
pub use clap; |
Traits
StructOpt | A struct that is converted from command line arguments. |