uu_printenv 0.0.1

printenv ~ (uutils) display value of environment VAR
Documentation 
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//  * This file is part of the uutils coreutils package.
//  *
//  * (c) Jordi Boggiano <j.boggiano@seld.be>
//  *
//  * For the full copyright and license information, please view the LICENSE
//  * file that was distributed with this source code.

/* last synced with: printenv (GNU coreutils) 8.13 */

extern crate getopts;

#[macro_use]
extern crate uucore;

use std::env;

static NAME: &str = "printenv";
static VERSION: &str = env!("CARGO_PKG_VERSION");

pub fn uumain(args: Vec<String>) -> i32 {
    let mut opts = getopts::Options::new();
    opts.optflag(
        "0",
        "null",
        "end each output line with 0 byte rather than newline",
    );
    opts.optflag("h", "help", "display this help and exit");
    opts.optflag("V", "version", "output version information and exit");
    let matches = match opts.parse(&args[1..]) {
        Ok(m) => m,
        Err(f) => crash!(1, "Invalid options\n{}", f),
    };
    if matches.opt_present("help") {
        let msg = format!(
            "{0} {1}

Usage:
  {0} [VARIABLE]... [OPTION]...

Prints the given environment VARIABLE(s), otherwise prints them all.",
            NAME, VERSION
        );
        print!("{}", opts.usage(&msg));
        return 0;
    }
    if matches.opt_present("version") {
        println!("{} {}", NAME, VERSION);
        return 0;
    }
    let mut separator = "\n";
    if matches.opt_present("null") {
        separator = "\x00";
    };

    exec(matches.free, separator);

    0
}

pub fn exec(args: Vec<String>, separator: &str) {
    if args.is_empty() {
        for (env_var, value) in env::vars() {
            print!("{}={}{}", env_var, value, separator);
        }
        return;
    }

    for env_var in &args {
        if let Ok(var) = env::var(env_var) {
            print!("{}{}", var, separator);
        }
    }
}