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# Argument parsing
Matching can be used to parse simple arguments:
```rust,editable
use std::env;
fn increase(number: i32) {
println!("{}", number + 1);
}
fn decrease(number: i32) {
println!("{}", number - 1);
}
fn help() {
println!("usage:
match_args <string>
Check whether given string is the answer.
match_args {{increase|decrease}} <integer>
Increase or decrease given integer by one.");
}
fn main() {
let args: Vec<String> = env::args().collect();
match args.len() {
// no arguments passed
1 => {
println!("My name is 'match_args'. Try passing some arguments!");
},
// one argument passed
2 => {
match args[1].parse() {
Ok(42) => println!("This is the answer!"),
_ => println!("This is not the answer."),
}
},
// one command and one argument passed
3 => {
let cmd = &args[1];
let num = &args[2];
// parse the number
let number: i32 = match num.parse() {
Ok(n) => {
n
},
Err(_) => {
eprintln!("error: second argument not an integer");
help();
return;
},
};
// parse the command
match &cmd[..] {
"increase" => increase(number),
"decrease" => decrease(number),
_ => {
eprintln!("error: invalid command");
help();
},
}
},
// all the other cases
_ => {
// show a help message
help();
}
}
}
```
```shell
$ ./match_args Rust
This is not the answer.
$ ./match_args 42
This is the answer!
$ ./match_args do something
error: second argument not an integer
usage:
match_args <string>
Check whether given string is the answer.
match_args {increase|decrease} <integer>
Increase or decrease given integer by one.
$ ./match_args do 42
error: invalid command
usage:
match_args <string>
Check whether given string is the answer.
match_args {increase|decrease} <integer>
Increase or decrease given integer by one.
$ ./match_args increase 42
43
```
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