Clap - short command line parameters

arg short

This is part of the series about Clap, the Command Line Argument Parser of Rust.

Having long command line parameter names is good, because they are usually easier to remember than the short ones, and they are clearer once you wrote them down, but they also take a lot longer to type in. So often, besides having a flag called --debug we would also like to allow the user to just write -d. In addition of --help Clap allows us to use the -h flag and get help. When we use the version command we automatically get two flags the --version and the -V flag. Apparently for some reason the "short name for the lower-case version is the upper-case V.

In order to allow short parameter name(s) we only have to supply the short keyword in the arg definition of each parameter where we want to have such a flag:

Short parameter names

debug: bool,

This will allow the user to use -d.

#[arg(long, short)]
debug: bool,

This will allow the user to use either -d or --debug.

#[arg(long, short)]
host: String,

This will lead to a runtime panic!:

Command short: Short option names must be unique for each argument, but '-h' is in use by both 'host' and 'help' (call `cmd.disable_help_flag(true)` to remove the auto-generated `--help`)

In addition to the solution suggested in this message we can also set the short letter explicitly:

#[arg(long, short='H')]
host: String,

As explained in this issue there is no plan to include this suggestion in the panic message.


As in the other articles about Clap I include the content of Cargo.toml to make it easier to copy this example.


name = "short"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at

clap = { version = "4.4.11", features = ["derive"] }

The full example


use clap::Parser;

struct Cli {
    #[arg(long, short, default_value_t = false)]
    debug: bool,

    #[arg(long, short='H', default_value = "")]
    host: String,

    verbose: bool,

fn main() {
    let args = Cli::parse();
    println!("debug:   {}", args.debug);
    println!("host:    {}",;
    println!("verbose: {}", args.verbose);

In this example I included the version command, long parameters, and default values as well.

Usage with defaults:

$ cargo run -q

debug:   false
verbose: false

Setting some parameters

$ cargo run -q -- -v -H localhost

debug:   false
host:    localhost
verbose: true

Here we can see that we can use the -H short name for --host and we can use -v for verbose. Maybe the reason the short of --version is the capital -V is to allow -v to be short of verbose.

Combining short flags

$ cargo run -q -- -dvH localhost

debug:   true
host:    localhost
verbose: true

We can even combine the short bool flags and the last one of the combination can also be a flag the expects a value.

Related Pages

Clap - Command Line Argument Parser for Rust


Gabor Szabo (szabgab)

Gabor Szabo, the author of the Rust Maven web site maintains several Open source projects in Rust and while he still feels he has tons of new things to learn about Rust he already offers training courses in Rust and still teaches Python, Perl, git, GitHub, GitLab, CI, and testing.

Gabor Szabo