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0.3.0 Nov 25, 2019
0.2.0 Nov 21, 2019
0.1.0 Nov 21, 2019

#616 in Command-line interface

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11,746 downloads per month
Used in 6 crates

MIT license

909 lines


An argument parser that is truly zero-cost, similar to Unix's getopts.


getargs is a low-level, efficient and versatile argument parser that works similarly to getopts. It works by producing a stream of options, and after each option, your code decides whether to require and retrieve the value for the option or not.

You don't have to declare a list of valid options up-front, so getargs does not have to allocate space for them or spend runtime searching for them. This also means that you have to write your own help message, but since --help is just another flag, there are no restrictions on what you do with it.


  • Short -f and long --flag flags
  • Required implicit values -i VALUE and --implicit VALUE
  • Required or optional explicit values -eVALUE and --explicit=VALUE
  • Positional arguments and --
  • Parse options at the beginning of the argument list, or anywhere


  • Zero cost
  • Zero copy
  • Zero unsafe code
  • Zero dependencies
  • Zero allocation
  • Simple to use yet versatile
  • #![no_std]-compatible
  • Compatible with &str and &[u8]


getargs has had a lot of attention put into profiling and optimization, and on a modern machine it takes under 0.2μs to parse a short array of 12 arguments.

In our testing, getargs is faster than every other argument parsing library on crates.io. Its closest competitor is gumdrop, which is only ~30% slower in the worst case, and its second-closest competitor is getopt, which takes three times as long. Other libraries degrade quickly; clap takes 45x longer. (This is not an entirely fair comparison though, as clap is not just an argument-parsing library, but an entire command-line application framework. It is perhaps overqualified for simple tasks.)


For examples, see [the examples directory][./examples/] for small programs that you can compile and run yourself to see how getargs works.



No runtime deps