Use variables as command arguments

Question

In a program I am trying to display the artwork of my currently playing spotify song using rust.

The code only works if I copy and paste the url into the argument, so I tried making a variable called arturl to use in a .arg(arturl). But that makes the code return nothing, and the arturl variable does return the correct value.

My code:

use std::process::{Command, Stdio};

fn main() {
    let arturl = Command::new("playerctl")
        .arg("metadata")
        .arg("mpris:artUrl")
        .stdout(Stdio::piped())
        .output()
        .expect("url failed");
    let arturl = String::from_utf8(arturl.stdout).unwrap();

    let picture = Command::new("chafa")
        .arg("--size=30")
        .arg(arturl)
        .stdout(Stdio::piped())
        .output()
        .expect("picture failed");
    let picture = String::from_utf8(picture.stdout).unwrap();
    println!("{}", picture);
}

What does this code print if you add println!("{:?}", arturl) (exactly this, with Debug formatting, to see possible unprintable symbols)? — Cerberus
– Cerberus, Commented May 22, 2022 at 5:53
Thanks this helps a whole lot, apparently there was a trailing new line in the string... — a e
– a e, Commented May 22, 2022 at 6:06

a e · Accepted Answer · 2022-05-22 06:08:13Z

1

Managed to fixed this with adding a simple arturl.pop to get rid of the newline at the end of the string

fixed code:

use std::process::{Command, Stdio};

fn main() {
    let arturl = Command::new("playerctl")
        .arg("metadata")
        .arg("mpris:artUrl")
        .stdout(Stdio::piped())
        .output()
        .expect("url failed");
    let mut arturl = String::from_utf8(arturl.stdout).unwrap();
    arturl.pop();
    println!("{:?}", arturl);

    let picture = Command::new("chafa")
        .arg("--size=30")
        .arg(arturl)
        .stdout(Stdio::piped())
        .output()
        .expect("picture failed");
    let picture = String::from_utf8(picture.stdout).unwrap();
    println!("{}", picture);
}

answered May 22, 2022 at 6:08

a e

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1 Comment

Cerberus Over a year ago

The more idiomatic solution would probably be to trim() the output, since this would more explicitly tell the intention. This wouldn't work if the URL can have legitimate spaces at the either end, however.

Netwave · Accepted Answer · 2022-05-22 09:26:02Z

1

You should probably "clean" the string with str::trim:

use std::process::{Command, Stdio};

fn main() {
    let arturl = Command::new("playerctl")
        .arg("metadata")
        .arg("mpris:artUrl")
        .stdout(Stdio::piped())
        .output()
        .expect("url failed");
    let arturl = String::from_utf8(arturl.stdout).unwrap().trim();
    println!("{:?}", arturl);

    let picture = Command::new("chafa")
        .arg("--size=30")
        .arg(arturl)
        .stdout(Stdio::piped())
        .output()
        .expect("picture failed");
    let picture = String::from_utf8(picture.stdout).unwrap();
    println!("{}", picture);
}

answered May 22, 2022 at 9:26

Netwave

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