Structopt: PathBuf w/ default of stdin?

[zack-emmert]

How does one specify a PathBuf parameter that defaults to stdin? The example in the docs say that it defaults to stdout.

[TeXitoi]

PathBuf represent a path to a file. stdin and stdout can't be modeled this way. The example saying that default to stdout is purely talking about what the application will do. For example, for your case, just use a Option, and do something like that:

#[macro_use]
extern crate structopt;

use structopt::StructOpt;
use std::io::{self, Read, Write};
use std::fs;
use std::path::PathBuf;

#[derive(StructOpt, Debug)]
struct Opt {
    /// Input file, default to stdin.
    #[structopt(short = "i", parse(from_os_str))]
    input: Option<PathBuf>,
    /// Output file, default to stdout.
    #[structopt(short = "o", parse(from_os_str))]
    output: Option<PathBuf>,
}

fn main() {
    run(Opt::from_args()).unwrap();
}

fn run(opt: Opt) -> io::Result<()> {
    match (opt.input, opt.output) {
        (None, None) => cat(io::stdin(), io::stdout())?,
        (Some(i), Some(o)) => cat(fs::File::open(i)?, fs::File::create(o)?)?,
        (None, Some(o)) => cat(io::stdin(), fs::File::create(o)?)?,
        (Some(i), None) => cat(fs::File::open(i)?, io::stdout())?,
    }
    Ok(())
}

fn cat<R: Read, W: Write>(reader: R, mut writer: W) -> io::Result<()> {
    for b in reader.bytes() {
        writer.write(&[b?])?;
    }
    Ok(())
}

[TeXitoi]

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