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Rust: command line parameter and environment variable operation
2020-11-08 08:59:55 【osc_sejgcp0】
Rust in , We often encounter command line parameters and environment variable operations . Let's have a look at .
One 、 Command line arguments
You can see from above ,std::env Realized from cargo run Command line parameters are extracted from the command line a b c Enter the program .
Two 、 Read environment variables
std::env::var function , The function of environment variable in operating system is realized .
env::var()-> std::env::Vars
Vars What is it? , Very complicated , He did Iterator. The following is the source code in the standard library :
#[stable(feature = "env", since = "1.0.0")]
pub struct Vars {
inner: VarsOs,
}
/// An iterator over a snapshot of the environment variables of this process.
///
/// This structure is created by the [`std::env::vars_os`] function. See
/// its documentation for more.
///
/// [`std::env::vars_os`]: vars_os
#[stable(feature = "env", since = "1.0.0")]
pub struct VarsOs {
inner: os_imp::Env,
}
It should be noted that , In the environment variables , Characters don't have to be Unicode The standard , That would be a false report . You can use :
env::vars_os
following : Read specific environment variables
use std::env;
fn main() {
let args: Vec<String> = env::args().collect();
//println!("get command args :{:?} ", args);
//println!("get env args : ");
for (key, value) in env::vars() {
//println!(" {} => {}", key, value);
}
let key = "PATH";
match env::var(key) {
Ok(val) => {
// val is String, splited by ";"
println!("val =>{}",val);
},
Err(e) => println!("couldn't interpret {}: {}", key, e),
}
}
3、 ... and 、 Set the environment variable
Generally include : View all environment variables 、 Set new environment variables and modify old environment variables .
1、 stay cmd Next
The settings are made above , View individual environment variable operations 、 Modify the operating . It's still relatively simple .
2、powshell
# View all environment variables ls env:
# Search for environment variables ls env:NODE*
# Look at a single environment variable $env:NODE_ENV
# add to / Update environment variables $env:NODE_ENV=development
# Delete environment variables del evn:NODE_ENV
3、linux
modify bashrc file , This method is safer , It can control the permission to use these environment variables to the user level , This is for a specific user , If you need to give a user permission to use these environment variables , You only need to modify the
.bashrc Just file it .vi ~/.bashrc
Add below :
Export PATH="$PATH:/NEW_PATH"
source :
https://www.cnblogs.com/Joans/p/7760378.html
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