pico-args 0.4.2

An ultra simple CLI arguments parser.


Build Status Crates.io Documentation Rust 1.32+

An ultra simple CLI arguments parser.

If you think that this library doesn't support some feature, it's probably intentional.

  • No help generation.
  • Only flags, options, free arguments and subcommands are supported.
  • Options can be separated by a space, = or nothing. See build features.
  • Arguments can be in any order.
  • Non UTF-8 arguments are supported.

Build features

  • eq-separator

    Allows parsing arguments separated by =. Enabled by default. This feature adds about 1KiB to the resulting binary.

  • short-space-opt

    Makes the space between short keys and their values optional (e.g. -w10). If eq-separator is enabled, then it takes precedence and the '=' is not included. If eq-separator is disabled, then -K=value gives an error instead of returning "=value". The optional space is only applicable for short keys because --keyvalue would be ambiguous.

  • combined-flags

    Allows combination of flags, e.g. -abc instead of -a -b -c. If short-space-opt or eq-separator are enabled, you must parse flags after values, to prevent ambiguities.


The core idea of pico-args is to provide some "sugar" for arguments parsing without a lot of overhead (binary or compilation time wise). There are no point in comparing parsing features since pico-args supports only the bare minimum. So we will compare only the size overhead and compilation time.

There are a lot of arguments parsing implementations, but we will use only these one:

  • clap - is the most popular and complete one
  • gumdrop - a simple parser that uses procedural macros
  • structopt - a two above combined
  • argh - similar to gumdrop
null pico-args clap gumdrop structopt argh
Binary overhead 0KiB 14.3KiB 373.0KiB 19.8KiB 371.4KiB 17.6KiB
Build time 0.4s 0.7s 5.6s 4.1s 6.2s 4.0s
Number of dependencies 0 0 8 5 20 8
Tested version - 0.4.0 2.33.3 0.8.0 0.3.21 0.1.4
  • Binary size overhead was measured by subtracting the .text section size of an app with arguments parsing and a hello world app.
  • Build time was measured using hyperfine 'cargo clean; cargo build --release'.
  • Test projects can be found in test-apps/.