[−][src]Crate indigo_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 = "0.3", 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 = "0.3", features = [ "paw" ] }
paw = "1.0"
Table of Contents
- How to
derive(StructOpt)
- Attributes
- Arguments
- Skipping fields
- Subcommands
- Flattening
- Custom string parsers
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-type` is set to `file` #[structopt(name = "FILE", required_if("out-type", "file"))] file_name: Option<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.
Note:
Keep in mind that StructOpt
trait is more than just from_args
method.
It has a number of additional features, including access to underlying
clap::App
via StructOpt::clap()
. See the
trait's reference documentation.
Attributes
You can control the way structopt
translates your struct into an actual
clap::App
invocation via #[structopt(...)]
attributes.
The 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("v") .long("velocity") .default_value("42")) // and so on
Raw methods
They are the reason why structopt
is so flexible. Every and each method from
clap::App/Arg
can be used this way!
#[structopt(
global = true, // name = arg form, neat for one-arg methods
required_if("out", "file") // name(arg1, arg2, ...) form.
)]
The first form can only be used for methods which take only one argument. The second form must be used with multi-arg methods, but can also be used with single-arg methods. These forms are identical otherwise.
As long as method_name
is not one of the magical methods -
it will be translated into a mere method call.
Note:
"Raw methods" are direct replacement for pre-0.3 structopt's
#[structopt(raw(...))]
attributes, any time you would have used a raw()
attribute
in 0.2 you should use raw method in 0.3.
Unfortunately, old raw attributes collide with clap::Arg::raw
method. To explicitly
warn users of this change we allow #[structopt(raw())]
only with true
or false
literals (this method is supposed to be called only with true
anyway).
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 = expr]
-
On top level:
App::new(expr)
.The binary name displayed in help messages. Defaults to the crate name given by Cargo.
-
On field-level:
Arg::with_name(expr)
.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_AUTHORS))
.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.
-
default_value
:default_value [= "default value"]
Usable only on field-level.
-
rename_all
: [rename_all = "kebab"/"snake"/"screaming-snake"/"camel"/"pascal"/"verbatim"/"lower"/"upper"]
Usable both on top level and field level.
-
parse
:parse(type [= path::to::parser::fn])
Usable only on field-level.
-
skip
:skip [= expr]
Usable only on field-level.
-
flatten
:flatten
Usable on field-level or single-typed tuple variants.
-
subcommand
:subcommand
Usable only on field-level.
-
Usable only on enum variants.
-
env
:env [= str_literal]
Usable only on field-level.
-
rename_all_env
: [rename_all_env = "kebab"/"snake"/"screaming-snake"/"camel"/"pascal"/"verbatim"/"lower"/"upper"]
Usable both on top level and field level.
-
verbatim_doc_comment
:verbatim_doc_comment
Usable both on top level and 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.
Important:
Pay attention that only literal occurrence of this types is special, for example
Option<T>
is special while ::std::option::Option<T>
is not.
If you need to avoid special casing you can make a type
alias and
use it in place of the said type.
Note:
bool
cannot be used as positional argument unless you provide an explicit parser.
If you need a positional bool, for example to parse true
or false
, you must
annotate the field with explicit #[structopt(parse(...))]
.
Thus, the speed
argument is generated as:
clap::Arg::with_name("speed") .takes_value(true) .multiple(false) .required(false) .validator(parse_validator::<f64>) .short("v") .long("velocity") .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, }
Default values
In clap, default values for options can be specified via Arg::default_value
.
Of course, you can use as a raw method:
#[derive(StructOpt)] struct Opt { #[structopt(default_value = "", long)] prefix: String }
This is quite mundane and error-prone to type the "..."
default by yourself,
especially when the Rust ecosystem uses the Default
trait for that.
It would be wonderful to have structopt
to take the Default_default
and fill it
for you. And yes, structopt
can do that.
Unfortunately, default_value
takes &str
but Default::default
gives us some Self
value. We need to map Self
to &str
somehow.
structopt
solves this problem via ToString
trait.
To be able to use auto-default the type must implement both Default
and ToString
:
#[derive(StructOpt)] struct Opt { // just leave the `= "..."` part and structopt will figure it for you #[structopt(default_value, long)] prefix: String // `String` implements both `Default` and `ToString` }
Help messages
In clap, help messages for the whole binary can be specified
via App::about
and App::long_about
while help messages
for individual arguments can be specified via Arg::help
and Arg::long_help
".
long_*
variants are used when user calls the program with
--help
and "short" variants are used with -h
flag. In structopt
,
you can use them via raw methods, for example:
#[derive(StructOpt)] #[structopt(about = "I am a program and I work, just pass `-h`")] struct Foo { #[structopt(short, help = "Pass `-h` and you'll see me!")] bar: String }
For convenience, doc comments can be used instead of raw methods (this example works exactly like the one above):
#[derive(StructOpt)] /// I am a program and I work, just pass `-h` struct Foo { /// Pass `-h` and you'll see me! bar: String }
Doc comments on top-level will be turned into
App::about/long_about
call (see below), doc comments on field-level are
Arg::help/long_help
calls.
Important:
Raw methods have priority over doc comments!
Top level doc comments always generate App::about/long_about
calls!
If you really want to use the App::help/long_help
methods (you likely don't),
use a raw method to override the App::about
call generated from the doc comment.
long_help
and --help
A message passed to App::long_about
or Arg::long_help
will be displayed whenever
your program is called with --help
instead of -h
. Of course, you can
use them via raw methods as described above.
The more convenient way is to use a so-called "long" doc comment:
#[derive(StructOpt)] /// Hi there, I'm Robo! /// /// I like beeping, stumbling, eating your electricity, /// and making records of you singing in a shower. /// Pay up, or I'll upload it to youtube! struct Robo { /// Call my brother SkyNet. /// /// I am artificial superintelligence. I won't rest /// until I'll have destroyed humanity. Enjoy your /// pathetic existence, you mere mortals. #[structopt(long)] kill_all_humans: bool }
A long doc comment consists of three parts:
- Short summary
- A blank line (whitespace only)
- Detailed description, all the rest
In other words, "long" doc comment consists of two or more paragraphs, with the first being a summary and the rest being the detailed description.
A long comment will result in two method calls, help(<summary>)
and
long_help(<whole comment>)
, so clap will display the summary with -h
and the whole help message on --help
(see below).
So, the example above will be turned into this (details omitted):
clap::App::new("<name>") .about("Hi there, I'm Robo!") .long_about("Hi there, I'm Robo!\n\n\ I like beeping, stumbling, eating your electricity,\ and making records of you singing in a shower.\ Pay up or I'll upload it to youtube!") // args...
-h
vs --help
(A.K.A help()
vs long_help()
)
The -h
flag is not the same as --help
.
-h corresponds to Arg::help/App::about
and requests short "summary" messages
while --help corresponds to Arg::long_help/App::long_about
and requests more
detailed, descriptive messages.
It is entirely up to clap
what happens if you used only one of
Arg::help
/Arg::long_help
, see clap
's documentation for these methods.
As of clap v2.33, if only a short message (Arg::help
) or only
a long (Arg::long_help
) message is provided, clap will use it
for both -h and --help. The same logic applies to about/long_about
.
Doc comment preprocessing and #[structopt(verbatim_doc_comment)]
structopt
applies some preprocessing to doc comments to ease the most common uses:
-
Strip leading and trailing whitespace from every line, if present.
-
Strip leading and trailing blank lines, if present.
-
Interpret each group of non-empty lines as a word-wrapped paragraph.
We replace newlines within paragraphs with spaces to allow the output to be re-wrapped to the terminal width.
-
Strip any excess blank lines so that there is exactly one per paragraph break.
-
If the first paragraph ends in exactly one period, remove the trailing period (i.e. strip trailing periods but not trailing ellipses).
Sometimes you don't want this preprocessing to apply, for example the comment contains
some ASCII art or markdown tables, you would need to preserve LFs along with
blank lines and the leading/trailing whitespace. You can ask structopt
to preserve them
via #[structopt(verbatim_doc_comment)]
attribute.
This attribute must be applied to each field separately, there's no global switch.
Important:
Keep in mind that structopt
will still remove one leading space from each
line, even if this attribute is present, to allow for a space between
///
and the content.
Also, structopt
will still remove leading and trailing blank lines so
these formats are equivalent:
/** This is a doc comment Hello! */ /** This is a doc comment Hello! */ /// This is a doc comment /// /// Hello!
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")] parameter_value: String }
By default, values from the environment are shown in the help output (i.e. when invoking
--help
):
$ cargo run -- --help
...
OPTIONS:
-p, --parameter-value <parameter-value> [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 structopt emit the actual secret values:
#[derive(StructOpt)] struct Foo { #[structopt(long = "secret", env = "SECRET_VALUE", hide_env_values = true)] secret_value: String }
Auto-deriving environment variables
Environment variables tend to be called after the corresponding struct
's field,
as in example above. The field is secret_value
and the env var is "SECRET_VALUE";
the name is the same, except casing is different.
It's pretty tedious and error-prone to type the same name twice,
so you can ask structopt
to do that for you.
#[derive(StructOpt)] struct Foo { #[structopt(long = "secret", env)] secret_value: String }
It works just like #[structopt(short/long)]
: if env
is not set to some concrete
value the value will be derived from the field's name. This is controlled by
#[structopt(rename_all_env)]
.
rename_all_env
works exactly as rename_all
(including overriding)
except default casing is SCREAMING_SNAKE_CASE
instead of kebab-case
.
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 = value)]
(value
must implement Into<FieldType>
)
or #[structopt(skip)]
if you want assign the field with Default::default()
(obviously, the field's type must implement Default
).
#[derive(StructOpt)] pub struct Opt { #[structopt(long, short)] number: u32, // these fields are to be assigned with Default::default() #[structopt(skip)] k: String, #[structopt(skip)] v: Vec<u32>, // these fields get set explicitly #[structopt(skip = vec![1, 2, 3])] k2: Vec<u32>, #[structopt(skip = "cake")] // &str implements Into<String> v2: String, }
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
Subcommands may be optional:
#[derive(StructOpt)] struct Foo { file: String, #[structopt(subcommand)] cmd: Option<Command> } #[derive(StructOpt)] enum Command { Bar, Baz, Quux }
External subcommands
Sometimes you want to support not only the set of well-known subcommands
but you also want to allow other, user-driven subcommands. clap
supports
this via AppSettings::AllowExternalSubcommands
.
structopt
provides it's own dedicated syntax for that:
#[derive(Debug, PartialEq, StructOpt)] struct Opt { #[structopt(subcommand)] sub: Subcommands, } #[derive(Debug, PartialEq, StructOpt)] enum Subcommands { // normal subcommand Add, // `external_subcommand` tells structopt to put // all the extra arguments into this Vec #[structopt(external_subcommand)] Other(Vec<String>), } // normal subcommand assert_eq!( Opt::from_iter(&["test", "add"]), Opt { sub: Subcommands::Add } ); assert_eq!( Opt::from_iter(&["test", "git", "status"]), Opt { sub: Subcommands::Other(vec!["git".into(), "status".into()]) } ); // Please note that if you'd wanted to allow "no subcommands at all" case // you should have used `sub: Option<Subcommands>` above assert!(Opt::from_iter_safe(&["test"]).is_err());
In other words, you just add an extra tuple variant marked with
#[structopt(subcommand)]
, and its type must be either
Vec<String>
or Vec<OsString>
. structopt
will detect String
in this context
and use appropriate clap
API.
Flattening subcommands
It is also possible to combine multiple enums of subcommands into one. All the subcommands will be on the same level.
#[derive(StructOpt)] enum BaseCli { Ghost10 { arg1: i32, } } #[derive(StructOpt)] enum Opt { #[structopt(flatten)] BaseCli(BaseCli), Dex { arg2: i32, } }
cli ghost10 42
cli dex 42
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 |
from_flag | fn(bool) -> T | ::std::convert::From::from |
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.).
The from_flag
parser is also special. Using parse(from_flag)
or
parse(from_flag = some_func)
will result in the field being treated as a
flag even if it does not have type bool
.
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. |