Function resolve_executable 

pub fn resolve_executable(
    program: &str,
    cwd: &Path,
    env: &[(String, String)],
) -> Option<PathBuf>

The executable program runs as in cwd with env: a program with a / against cwd, else the first file of that name on PATH (relative PATH entries against cwd too) — canonicalised; None when there is none. A file without an execute bit is skipped, as execvp skips it: the executable named is the one that runs. What a command’s approval names, and what it is checked against again when it runs.