Error

Additional Language Notes

1. While error may be used as a type annotation, there is currently no known use-case for doing so, since an error value can never be assigned to a variable or custom command parameter. Any error condition results in termination of the current command/expression and will also terminate any assignment expression or custom command. For example:

   let e: error = (error make --unspanned { msg: "This is an error" })
   # => Error: nu::shell::error
   # =>
   # =>   × This is an error
   # =>
   
   $e
   # => Error: nu::shell::variable_not_found
   # =>
   # =>   × Variable not found
   # =>    ╭─[repl_entry #2:1:1]
   # =>  1 │ $e
   # =>    · ─┬
   # =>    ·  ╰── variable not found
   # =>    ╰────

2. The error type is also returned from internal Nushell commands to indicate an error condition, but as with assignment, there is no way to use this result.

3. Surrounding code that might potentially throw an error with a try/catch {|e|} block will result in an $e variable that is a record, not an error type.

   The record has the fields msg, debug, raw, rendered and details. details is a record with the msg, labels, code, url, help and inner of the error:

   try { 1 / 0 } catch {|e| $e.msg }
   # => Division by zero.
   try { 1 / 0 } catch {|e| $e.details.code }
   # => nu::shell::division_by_zero

   The raw field holds the original error value. Evaluating it raises the error again, so it can be used to re-throw an error after handling it:

   try { 1 / 0 } catch {|e| print "cleaning up"; $e.raw }
   # => cleaning up
   # => Error: nu::shell::division_by_zero
   # =>
   # =>   × Division by zero.
   # =>    ╭─[repl_entry #1:1:9]
   # =>  1 │ try { 1 / 0 } catch {|e| print "cleaning up"; $e.raw }
   # =>    ·         ┬
   # =>    ·         ╰── division by zero
   # =>    ╰────

   See try/catch for more about handling errors.