Available on crate feature
unstable-doc only.Expand description
§Tutorial for the Builder API
See the side bar for the Table of Contents
§Quick Start
You can create an application with several arguments using usage strings.
First, ensure clap is available:
$ cargo add clapHere is a preview of the type of application you can make:
use std::path::PathBuf;
use clap::{arg, command, value_parser, ArgAction, Command};
fn main() {
let matches = command!() // requires `cargo` feature
.arg(arg!([name] "Optional name to operate on"))
.arg(
arg!(
-c --config <FILE> "Sets a custom config file"
)
// We don't have syntax yet for optional options, so manually calling `required`
.required(false)
.value_parser(value_parser!(PathBuf)),
)
.arg(arg!(
-d --debug ... "Turn debugging information on"
))
.subcommand(
Command::new("test")
.about("does testing things")
.arg(arg!(-l --list "lists test values").action(ArgAction::SetTrue)),
)
.get_matches();
// You can check the value provided by positional arguments, or option arguments
if let Some(name) = matches.get_one::<String>("name") {
println!("Value for name: {name}");
}
if let Some(config_path) = matches.get_one::<PathBuf>("config") {
println!("Value for config: {}", config_path.display());
}
// You can see how many times a particular flag or argument occurred
// Note, only flags can have multiple occurrences
match matches
.get_one::<u8>("debug")
.expect("Counts are defaulted")
{
0 => println!("Debug mode is off"),
1 => println!("Debug mode is kind of on"),
2 => println!("Debug mode is on"),
_ => println!("Don't be crazy"),
}
// You can check for the existence of subcommands, and if found use their
// matches just as you would the top level cmd
if let Some(matches) = matches.subcommand_matches("test") {
// "$ myapp test" was run
if matches.get_flag("list") {
// "$ myapp test -l" was run
println!("Printing testing lists...");
} else {
println!("Not printing testing lists...");
}
}
// Continued program logic goes here...
}$ 01_quick --help
A simple to use, efficient, and full-featured Command Line Argument Parser
Usage: 01_quick[EXE] [OPTIONS] [name] [COMMAND]
Commands:
test does testing things
help Print this message or the help of the given subcommand(s)
Arguments:
[name] Optional name to operate on
Options:
-c, --config <FILE> Sets a custom config file
-d, --debug... Turn debugging information on
-h, --help Print help
-V, --version Print version
By default, the program does nothing:
$ 01_quick
Debug mode is off
But you can mix and match the various features
$ 01_quick -dd test
Debug mode is on
Not printing testing lists...
See also
- FAQ: When should I use the builder vs derive APIs?
- The cookbook for more application-focused examples
§Configuring the Parser
You use Command to start building a parser.
use clap::{arg, Command};
fn main() {
let matches = Command::new("MyApp")
.version("1.0")
.about("Does awesome things")
.arg(arg!(--two <VALUE>).required(true))
.arg(arg!(--one <VALUE>).required(true))
.get_matches();
println!(
"two: {:?}",
matches.get_one::<String>("two").expect("required")
);
println!(
"one: {:?}",
matches.get_one::<String>("one").expect("required")
);
}$ 02_apps --help
Does awesome things
Usage: 02_apps[EXE] --two <VALUE> --one <VALUE>
Options:
--two <VALUE>
--one <VALUE>
-h, --help Print help
-V, --version Print version
$ 02_apps --version
MyApp 1.0
You can use command!() to fill these fields in from your Cargo.toml
file. This requires the cargo feature flag.
use clap::{arg, command};
fn main() {
// requires `cargo` feature, reading name, version, author, and description from `Cargo.toml`
let matches = command!()
.arg(arg!(--two <VALUE>).required(true))
.arg(arg!(--one <VALUE>).required(true))
.get_matches();
println!(
"two: {:?}",
matches.get_one::<String>("two").expect("required")
);
println!(
"one: {:?}",
matches.get_one::<String>("one").expect("required")
);
}$ 02_crate --help
A simple to use, efficient, and full-featured Command Line Argument Parser
Usage: 02_crate[EXE] --two <VALUE> --one <VALUE>
Options:
--two <VALUE>
--one <VALUE>
-h, --help Print help
-V, --version Print version
$ 02_crate --version
clap [..]
You can use Command methods to change the application level behavior of
clap, like Command::next_line_help.
use clap::{arg, command, ArgAction};
fn main() {
let matches = command!() // requires `cargo` feature
.next_line_help(true)
.arg(arg!(--two <VALUE>).required(true).action(ArgAction::Set))
.arg(arg!(--one <VALUE>).required(true).action(ArgAction::Set))
.get_matches();
println!(
"two: {:?}",
matches.get_one::<String>("two").expect("required")
);
println!(
"one: {:?}",
matches.get_one::<String>("one").expect("required")
);
}$ 02_app_settings --help
A simple to use, efficient, and full-featured Command Line Argument Parser
Usage: 02_app_settings[EXE] --two <VALUE> --one <VALUE>
Options:
--two <VALUE>
--one <VALUE>
-h, --help
Print help
-V, --version
Print version
§Adding Arguments
§Positionals
By default, an Arg defines a positional argument:
use clap::{command, Arg};
fn main() {
let matches = command!() // requires `cargo` feature
.arg(Arg::new("name"))
.get_matches();
println!("name: {:?}", matches.get_one::<String>("name"));
}$ 03_03_positional --help
A simple to use, efficient, and full-featured Command Line Argument Parser
Usage: 03_03_positional[EXE] [name]
Arguments:
[name]
Options:
-h, --help Print help
-V, --version Print version
$ 03_03_positional
name: None
$ 03_03_positional bob
name: Some("bob")
Note that the default ArgAction is Set. To
accept multiple values, override the action with Append:
use clap::{command, Arg, ArgAction};
fn main() {
let matches = command!() // requires `cargo` feature
.arg(Arg::new("name").action(ArgAction::Append))
.get_matches();
let args = matches
.get_many::<String>("name")
.unwrap_or_default()
.map(|v| v.as_str())
.collect::<Vec<_>>();
println!("names: {:?}", &args);
}$ 03_03_positional_mult --help
A simple to use, efficient, and full-featured Command Line Argument Parser
Usage: 03_03_positional_mult[EXE] [name]...
Arguments:
[name]...
Options:
-h, --help Print help
-V, --version Print version
$ 03_03_positional_mult
names: []
$ 03_03_positional_mult bob
names: ["bob"]
$ 03_03_positional_mult bob john
names: ["bob", "john"]
§Options
You can name your arguments with a flag:
- Intent of the value is clearer
- Order doesn’t matter
use clap::{command, Arg};
fn main() {
let matches = command!() // requires `cargo` feature
.arg(Arg::new("name").short('n').long("name"))
.get_matches();
println!("name: {:?}", matches.get_one::<String>("name"));
}$ 03_02_option --help
A simple to use, efficient, and full-featured Command Line Argument Parser
Usage: 03_02_option[EXE] [OPTIONS]
Options:
-n, --name <name>
-h, --help Print help
-V, --version Print version
$ 03_02_option
name: None
$ 03_02_option --name bob
name: Some("bob")
$ 03_02_option --name=bob
name: Some("bob")
$ 03_02_option -n bob
name: Some("bob")
$ 03_02_option -n=bob
name: Some("bob")
$ 03_02_option -nbob
name: Some("bob")
Note that the default ArgAction is Set. To
accept multiple occurrences, override the action with Append:
use clap::{command, Arg, ArgAction};
fn main() {
let matches = command!() // requires `cargo` feature
.arg(
Arg::new("name")
.short('n')
.long("name")
.action(ArgAction::Append),
)
.get_matches();
let args = matches
.get_many::<String>("name")
.unwrap_or_default()
.map(|v| v.as_str())
.collect::<Vec<_>>();
println!("names: {:?}", &args);
}$ 03_02_option_mult --help
A simple to use, efficient, and full-featured Command Line Argument Parser
Usage: 03_02_option_mult[EXE] [OPTIONS]
Options:
-n, --name <name>
-h, --help Print help
-V, --version Print version
$ 03_02_option_mult
names: []
$ 03_02_option_mult --name bob
names: ["bob"]
$ 03_02_option_mult --name bob --name john
names: ["bob", "john"]
$ 03_02_option_mult_derive --name bob --name=john -n tom -n=chris -nsteve
name: ["bob", "john", "tom", "chris", "steve"]
§Flags
Flags can also be switches that can be on/off:
use clap::{command, Arg, ArgAction};
fn main() {
let matches = command!() // requires `cargo` feature
.arg(
Arg::new("verbose")
.short('v')
.long("verbose")
.action(ArgAction::SetTrue),
)
.get_matches();
println!("verbose: {:?}", matches.get_flag("verbose"));
}$ 03_01_flag_bool --help
A simple to use, efficient, and full-featured Command Line Argument Parser
Usage: 03_01_flag_bool[EXE] [OPTIONS]
Options:
-v, --verbose
-h, --help Print help
-V, --version Print version
$ 03_01_flag_bool
verbose: false
$ 03_01_flag_bool --verbose
verbose: true
$ 03_01_flag_bool --verbose --verbose
? failed
error: the argument '--verbose' cannot be used multiple times
Usage: 03_01_flag_bool[EXE] [OPTIONS]
For more information, try '--help'.
To accept multiple flags, use Count:
use clap::{command, Arg, ArgAction};
fn main() {
let matches = command!() // requires `cargo` feature
.arg(
Arg::new("verbose")
.short('v')
.long("verbose")
.action(ArgAction::Count),
)
.get_matches();
println!("verbose: {:?}", matches.get_count("verbose"));
}$ 03_01_flag_count --help
A simple to use, efficient, and full-featured Command Line Argument Parser
Usage: 03_01_flag_count[EXE] [OPTIONS]
Options:
-v, --verbose...
-h, --help Print help
-V, --version Print version
$ 03_01_flag_count
verbose: 0
$ 03_01_flag_count --verbose
verbose: 1
$ 03_01_flag_count --verbose --verbose
verbose: 2
§Required
By default, an Arg is optional which can be changed with
required.
use clap::{command, Arg};
fn main() {
let matches = command!() // requires `cargo` feature
.arg(Arg::new("name").required(true))
.get_matches();
println!(
"name: {:?}",
matches
.get_one::<String>("name")
.expect("clap `required` ensures its present")
);
}$ 03_06_required --help
A simple to use, efficient, and full-featured Command Line Argument Parser
Usage: 03_06_required[EXE] <name>
Arguments:
<name>
Options:
-h, --help Print help
-V, --version Print version
$ 03_06_required
? 2
error: the following required arguments were not provided:
<name>
Usage: 03_06_required[EXE] <name>
For more information, try '--help'.
$ 03_06_required bob
name: "bob"
§Defaults
We’ve previously showed that arguments can be required or optional.
When optional, you work with a Option and can unwrap_or. Alternatively, you can set
Arg::default_value.
use clap::{arg, command, value_parser};
fn main() {
let matches = command!() // requires `cargo` feature
.arg(
arg!([PORT])
.value_parser(value_parser!(u16))
.default_value("2020"),
)
.get_matches();
println!(
"port: {:?}",
matches
.get_one::<u16>("PORT")
.expect("default ensures there is always a value")
);
}$ 03_05_default_values --help
A simple to use, efficient, and full-featured Command Line Argument Parser
Usage: 03_05_default_values[EXE] [PORT]
Arguments:
[PORT] [default: 2020]
Options:
-h, --help Print help
-V, --version Print version
$ 03_05_default_values
port: 2020
$ 03_05_default_values 22
port: 22
§Subcommands
Subcommands are defined as Commands that get added via
Command::subcommand. Each instance of a Subcommand can have its
own version, author(s), Args, and even its own subcommands.
use clap::{arg, command, Command};
fn main() {
let matches = command!() // requires `cargo` feature
.propagate_version(true)
.subcommand_required(true)
.arg_required_else_help(true)
.subcommand(
Command::new("add")
.about("Adds files to myapp")
.arg(arg!([NAME])),
)
.get_matches();
match matches.subcommand() {
Some(("add", sub_matches)) => println!(
"'myapp add' was used, name is: {:?}",
sub_matches.get_one::<String>("NAME")
),
_ => unreachable!("Exhausted list of subcommands and subcommand_required prevents `None`"),
}
}$ 03_04_subcommands help
A simple to use, efficient, and full-featured Command Line Argument Parser
Usage: 03_04_subcommands[EXE] <COMMAND>
Commands:
add Adds files to myapp
help Print this message or the help of the given subcommand(s)
Options:
-h, --help Print help
-V, --version Print version
$ 03_04_subcommands help add
Adds files to myapp
Usage: 03_04_subcommands[EXE] add [NAME]
Arguments:
[NAME]
Options:
-h, --help Print help
-V, --version Print version
$ 03_04_subcommands add bob
'myapp add' was used, name is: Some("bob")
Because we set Command::arg_required_else_help:
$ 03_04_subcommands
? failed
A simple to use, efficient, and full-featured Command Line Argument Parser
Usage: 03_04_subcommands[EXE] <COMMAND>
Commands:
add Adds files to myapp
help Print this message or the help of the given subcommand(s)
Options:
-h, --help Print help
-V, --version Print version
Since we specified Command::propagate_version, the --version flag
is available in all subcommands:
$ 03_04_subcommands --version
clap [..]
$ 03_04_subcommands add --version
clap-add [..]
§Validation
An appropriate default parser/validator will be selected for the field’s type. See
value_parser! for more details.
§Enumerated values
If you have arguments of specific values you want to test for, you can use the
PossibleValuesParser or Arg::value_parser(["val1", ...]) for short.
This allows you to specify the valid values for that argument. If the user does not use one of those specific values, they will receive a graceful exit with error message informing them of the mistake, and what the possible valid values are
use clap::{arg, command};
fn main() {
let matches = command!() // requires `cargo` feature
.arg(
arg!(<MODE>)
.help("What mode to run the program in")
.value_parser(["fast", "slow"]),
)
.get_matches();
// Note, it's safe to call unwrap() because the arg is required
match matches
.get_one::<String>("MODE")
.expect("'MODE' is required and parsing will fail if its missing")
.as_str()
{
"fast" => {
println!("Hare");
}
"slow" => {
println!("Tortoise");
}
_ => unreachable!(),
}
}$ 04_01_possible --help
A simple to use, efficient, and full-featured Command Line Argument Parser
Usage: 04_01_possible[EXE] <MODE>
Arguments:
<MODE> What mode to run the program in [possible values: fast, slow]
Options:
-h, --help Print help
-V, --version Print version
$ 04_01_possible fast
Hare
$ 04_01_possible slow
Tortoise
$ 04_01_possible medium
? failed
error: invalid value 'medium' for '<MODE>'
[possible values: fast, slow]
For more information, try '--help'.
When enabling the derive feature, you can use
ValueEnum to take care of the boiler plate for you, giving the same
results.
use clap::{arg, builder::PossibleValue, command, value_parser, ValueEnum};
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
enum Mode {
Fast,
Slow,
}
// Can also be derived with feature flag `derive`
impl ValueEnum for Mode {
fn value_variants<'a>() -> &'a [Self] {
&[Mode::Fast, Mode::Slow]
}
fn to_possible_value(&self) -> Option<PossibleValue> {
Some(match self {
Mode::Fast => PossibleValue::new("fast").help("Run swiftly"),
Mode::Slow => PossibleValue::new("slow").help("Crawl slowly but steadily"),
})
}
}
impl std::fmt::Display for Mode {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
self.to_possible_value()
.expect("no values are skipped")
.get_name()
.fmt(f)
}
}
impl std::str::FromStr for Mode {
type Err = String;
fn from_str(s: &str) -> Result<Self, Self::Err> {
for variant in Self::value_variants() {
if variant.to_possible_value().unwrap().matches(s, false) {
return Ok(*variant);
}
}
Err(format!("invalid variant: {s}"))
}
}
fn main() {
let matches = command!() // requires `cargo` feature
.arg(
arg!(<MODE>)
.help("What mode to run the program in")
.value_parser(value_parser!(Mode)),
)
.get_matches();
// Note, it's safe to call unwrap() because the arg is required
match matches
.get_one::<Mode>("MODE")
.expect("'MODE' is required and parsing will fail if its missing")
{
Mode::Fast => {
println!("Hare");
}
Mode::Slow => {
println!("Tortoise");
}
}
}$ 04_01_enum --help
A simple to use, efficient, and full-featured Command Line Argument Parser
Usage: 04_01_enum[EXE] <MODE>
Arguments:
<MODE>
What mode to run the program in
Possible values:
- fast: Run swiftly
- slow: Crawl slowly but steadily
Options:
-h, --help
Print help (see a summary with '-h')
-V, --version
Print version
$ 04_01_enum -h
A simple to use, efficient, and full-featured Command Line Argument Parser
Usage: 04_01_enum[EXE] <MODE>
Arguments:
<MODE> What mode to run the program in [possible values: fast, slow]
Options:
-h, --help Print help (see more with '--help')
-V, --version Print version
$ 04_01_enum fast
Hare
$ 04_01_enum slow
Tortoise
$ 04_01_enum medium
? failed
error: invalid value 'medium' for '<MODE>'
[possible values: fast, slow]
For more information, try '--help'.
§Validated values
More generally, you can validate and parse into any data type with Arg::value_parser.
use clap::{arg, command, value_parser};
fn main() {
let matches = command!() // requires `cargo` feature
.arg(
arg!(<PORT>)
.help("Network port to use")
.value_parser(value_parser!(u16).range(1..)),
)
.get_matches();
// Note, it's safe to call unwrap() because the arg is required
let port: u16 = *matches
.get_one::<u16>("PORT")
.expect("'PORT' is required and parsing will fail if its missing");
println!("PORT = {port}");
}$ 04_02_parse --help
A simple to use, efficient, and full-featured Command Line Argument Parser
Usage: 04_02_parse[EXE] <PORT>
Arguments:
<PORT> Network port to use
Options:
-h, --help Print help
-V, --version Print version
$ 04_02_parse 22
PORT = 22
$ 04_02_parse foobar
? failed
error: invalid value 'foobar' for '<PORT>': invalid digit found in string
For more information, try '--help'.
$ 04_02_parse_derive 0
? failed
error: invalid value '0' for '<PORT>': 0 is not in 1..=65535
For more information, try '--help'.
A custom parser can be used to improve the error messages or provide additional validation:
use std::ops::RangeInclusive;
use clap::{arg, command};
fn main() {
let matches = command!() // requires `cargo` feature
.arg(
arg!(<PORT>)
.help("Network port to use")
.value_parser(port_in_range),
)
.get_matches();
// Note, it's safe to call unwrap() because the arg is required
let port: u16 = *matches
.get_one::<u16>("PORT")
.expect("'PORT' is required and parsing will fail if its missing");
println!("PORT = {port}");
}
const PORT_RANGE: RangeInclusive<usize> = 1..=65535;
fn port_in_range(s: &str) -> Result<u16, String> {
let port: usize = s
.parse()
.map_err(|_| format!("`{s}` isn't a port number"))?;
if PORT_RANGE.contains(&port) {
Ok(port as u16)
} else {
Err(format!(
"port not in range {}-{}",
PORT_RANGE.start(),
PORT_RANGE.end()
))
}
}$ 04_02_validate --help
A simple to use, efficient, and full-featured Command Line Argument Parser
Usage: 04_02_validate[EXE] <PORT>
Arguments:
<PORT> Network port to use
Options:
-h, --help Print help
-V, --version Print version
$ 04_02_validate 22
PORT = 22
$ 04_02_validate foobar
? failed
error: invalid value 'foobar' for '<PORT>': `foobar` isn't a port number
For more information, try '--help'.
$ 04_02_validate 0
? failed
error: invalid value '0' for '<PORT>': port not in range 1-65535
For more information, try '--help'.
See Arg::value_parser for more details.
§Argument Relations
You can declare dependencies or conflicts between Args or even
ArgGroups.
ArgGroups make it easier to declare relations instead of having to list
each individually, or when you want a rule to apply “any but not all” arguments.
Perhaps the most common use of ArgGroups is to require one and only one
argument to be present out of a given set. Imagine that you had multiple arguments, and you
want one of them to be required, but making all of them required isn’t feasible because perhaps
they conflict with each other.
use std::path::PathBuf;
use clap::{arg, command, value_parser, ArgAction, ArgGroup};
fn main() {
// Create application like normal
let matches = command!() // requires `cargo` feature
// Add the version arguments
.arg(arg!(--"set-ver" <VER> "set version manually"))
.arg(arg!(--major "auto inc major").action(ArgAction::SetTrue))
.arg(arg!(--minor "auto inc minor").action(ArgAction::SetTrue))
.arg(arg!(--patch "auto inc patch").action(ArgAction::SetTrue))
// Create a group, make it required, and add the above arguments
.group(
ArgGroup::new("vers")
.required(true)
.args(["set-ver", "major", "minor", "patch"]),
)
// Arguments can also be added to a group individually, these two arguments
// are part of the "input" group which is not required
.arg(
arg!([INPUT_FILE] "some regular input")
.value_parser(value_parser!(PathBuf))
.group("input"),
)
.arg(
arg!(--"spec-in" <SPEC_IN> "some special input argument")
.value_parser(value_parser!(PathBuf))
.group("input"),
)
// Now let's assume we have a -c [config] argument which requires one of
// (but **not** both) the "input" arguments
.arg(
arg!(config: -c <CONFIG>)
.value_parser(value_parser!(PathBuf))
.requires("input"),
)
.get_matches();
// Let's assume the old version 1.2.3
let mut major = 1;
let mut minor = 2;
let mut patch = 3;
// See if --set-ver was used to set the version manually
let version = if let Some(ver) = matches.get_one::<String>("set-ver") {
ver.to_owned()
} else {
// Increment the one requested (in a real program, we'd reset the lower numbers)
let (maj, min, pat) = (
matches.get_flag("major"),
matches.get_flag("minor"),
matches.get_flag("patch"),
);
match (maj, min, pat) {
(true, _, _) => major += 1,
(_, true, _) => minor += 1,
(_, _, true) => patch += 1,
_ => unreachable!(),
};
format!("{major}.{minor}.{patch}")
};
println!("Version: {version}");
// Check for usage of -c
if matches.contains_id("config") {
let input = matches
.get_one::<PathBuf>("INPUT_FILE")
.unwrap_or_else(|| matches.get_one::<PathBuf>("spec-in").unwrap())
.display();
println!(
"Doing work using input {} and config {}",
input,
matches.get_one::<PathBuf>("config").unwrap().display()
);
}
}$ 04_03_relations --help
A simple to use, efficient, and full-featured Command Line Argument Parser
Usage: 04_03_relations[EXE] [OPTIONS] <--set-ver <VER>|--major|--minor|--patch> [INPUT_FILE]
Arguments:
[INPUT_FILE] some regular input
Options:
--set-ver <VER> set version manually
--major auto inc major
--minor auto inc minor
--patch auto inc patch
--spec-in <SPEC_IN> some special input argument
-c <CONFIG>
-h, --help Print help
-V, --version Print version
$ 04_03_relations
? failed
error: the following required arguments were not provided:
<--set-ver <VER>|--major|--minor|--patch>
Usage: 04_03_relations[EXE] <--set-ver <VER>|--major|--minor|--patch> [INPUT_FILE]
For more information, try '--help'.
$ 04_03_relations --major
Version: 2.2.3
$ 04_03_relations --major --minor
? failed
error: the argument '--major' cannot be used with '--minor'
Usage: 04_03_relations[EXE] <--set-ver <VER>|--major|--minor|--patch> [INPUT_FILE]
For more information, try '--help'.
$ 04_03_relations --major -c config.toml
? failed
error: the following required arguments were not provided:
<INPUT_FILE|--spec-in <SPEC_IN>>
Usage: 04_03_relations[EXE] -c <CONFIG> <--set-ver <VER>|--major|--minor|--patch> <INPUT_FILE|--spec-in <SPEC_IN>>
For more information, try '--help'.
$ 04_03_relations --major -c config.toml --spec-in input.txt
Version: 2.2.3
Doing work using input input.txt and config config.toml
§Custom Validation
As a last resort, you can create custom errors with the basics of clap’s formatting.
use std::path::PathBuf;
use clap::error::ErrorKind;
use clap::{arg, command, value_parser, ArgAction};
fn main() {
// Create application like normal
let mut cmd = command!() // requires `cargo` feature
// Add the version arguments
.arg(arg!(--"set-ver" <VER> "set version manually"))
.arg(arg!(--major "auto inc major").action(ArgAction::SetTrue))
.arg(arg!(--minor "auto inc minor").action(ArgAction::SetTrue))
.arg(arg!(--patch "auto inc patch").action(ArgAction::SetTrue))
// Arguments can also be added to a group individually, these two arguments
// are part of the "input" group which is not required
.arg(arg!([INPUT_FILE] "some regular input").value_parser(value_parser!(PathBuf)))
.arg(
arg!(--"spec-in" <SPEC_IN> "some special input argument")
.value_parser(value_parser!(PathBuf)),
)
// Now let's assume we have a -c [config] argument which requires one of
// (but **not** both) the "input" arguments
.arg(arg!(config: -c <CONFIG>).value_parser(value_parser!(PathBuf)));
let matches = cmd.get_matches_mut();
// Let's assume the old version 1.2.3
let mut major = 1;
let mut minor = 2;
let mut patch = 3;
// See if --set-ver was used to set the version manually
let version = if let Some(ver) = matches.get_one::<String>("set-ver") {
if matches.get_flag("major") || matches.get_flag("minor") || matches.get_flag("patch") {
cmd.error(
ErrorKind::ArgumentConflict,
"Can't do relative and absolute version change",
)
.exit();
}
ver.to_string()
} else {
// Increment the one requested (in a real program, we'd reset the lower numbers)
let (maj, min, pat) = (
matches.get_flag("major"),
matches.get_flag("minor"),
matches.get_flag("patch"),
);
match (maj, min, pat) {
(true, false, false) => major += 1,
(false, true, false) => minor += 1,
(false, false, true) => patch += 1,
_ => {
cmd.error(
ErrorKind::ArgumentConflict,
"Can only modify one version field",
)
.exit();
}
};
format!("{major}.{minor}.{patch}")
};
println!("Version: {version}");
// Check for usage of -c
if matches.contains_id("config") {
let input = matches
.get_one::<PathBuf>("INPUT_FILE")
.or_else(|| matches.get_one::<PathBuf>("spec-in"))
.unwrap_or_else(|| {
cmd.error(
ErrorKind::MissingRequiredArgument,
"INPUT_FILE or --spec-in is required when using --config",
)
.exit()
})
.display();
println!(
"Doing work using input {} and config {}",
input,
matches.get_one::<PathBuf>("config").unwrap().display()
);
}
}$ 04_04_custom --help
A simple to use, efficient, and full-featured Command Line Argument Parser
Usage: 04_04_custom[EXE] [OPTIONS] [INPUT_FILE]
Arguments:
[INPUT_FILE] some regular input
Options:
--set-ver <VER> set version manually
--major auto inc major
--minor auto inc minor
--patch auto inc patch
--spec-in <SPEC_IN> some special input argument
-c <CONFIG>
-h, --help Print help
-V, --version Print version
$ 04_04_custom
? failed
error: Can only modify one version field
Usage: 04_04_custom[EXE] [OPTIONS] [INPUT_FILE]
For more information, try '--help'.
$ 04_04_custom --major
Version: 2.2.3
$ 04_04_custom --major --minor
? failed
error: Can only modify one version field
Usage: 04_04_custom[EXE] [OPTIONS] [INPUT_FILE]
For more information, try '--help'.
$ 04_04_custom --major -c config.toml
? failed
Version: 2.2.3
error: INPUT_FILE or --spec-in is required when using --config
Usage: 04_04_custom[EXE] [OPTIONS] [INPUT_FILE]
For more information, try '--help'.
$ 04_04_custom --major -c config.toml --spec-in input.txt
Version: 2.2.3
Doing work using input input.txt and config config.toml
§Testing
clap reports most development errors as debug_assert!s. Rather than checking every
subcommand, you should have a test that calls
Command::debug_assert:
use clap::{arg, command, value_parser};
fn main() {
let matches = cmd().get_matches();
// Note, it's safe to call unwrap() because the arg is required
let port: usize = *matches
.get_one::<usize>("PORT")
.expect("'PORT' is required and parsing will fail if its missing");
println!("PORT = {port}");
}
fn cmd() -> clap::Command {
command!() // requires `cargo` feature
.arg(
arg!(<PORT>)
.help("Network port to use")
.value_parser(value_parser!(usize)),
)
}
#[test]
fn verify_cmd() {
cmd().debug_assert();
}§Next Steps
- Cookbook for application-focused examples
- Explore more features in the API reference
For support, see Discussions