go/src/os/exec/lp_unix.go

var ErrNotFound …

func findExecutable(file string) error { … }

// LookPath searches for an executable named file in the
// directories named by the PATH environment variable.
// If file contains a slash, it is tried directly and the PATH is not consulted.
// Otherwise, on success, the result is an absolute path.
//
// In older versions of Go, LookPath could return a path relative to the current directory.
// As of Go 1.19, LookPath will instead return that path along with an error satisfying
// [errors.Is](err, [ErrDot]). See the package documentation for more details.
func LookPath(file string) (string, error) { … }

// lookExtensions is a no-op on non-Windows platforms, since
// they do not restrict executables to specific extensions.
func lookExtensions(path, dir string) (string, error) { … }