Error

Error is raised for system and I/O failures originating from the shell extension. It is a subtype of std.RuntimeError, so it can be caught either specifically or through the broader runtime error type.

try
  fs.read "/definitely/missing"
catch Error: err
  echo $str(err)

str(err) returns the underlying system error message. dbg(err) includes the nominal type name together with that message.

On Unix, Error exposes an errno field containing the underlying OS error number when one exists:

try
  fs.read "/definitely/missing"
catch Error: err
  assert_eq $err.errno 2

If the failure did not originate from an OS errno, errno is nil.