Macro runcmd_output 

macro_rules! runcmd_output {
    ($cmd:expr) => { ... };
    ($cmd:expr, $($args:expr),*) => { ... };
}

Runs the provided command, captures its stdout, and swallows its stderr except on failure. The first macro argument is the executable, and following arguments are passed to the command. Returns a Result describing whether the command failed, and if not, its standard output. Output is assumed to be UTF-8. Errors are adequately prefixed with the full command.