Nushell Error Handling with `error make` and `try`, and Early Returns

[`continue`](/commands/docs/continue.html) will stop execution of the current loop, skipping the rest of the code in the loop, and will go to the next loop. If the loop would normally end, like if [`for`](/commands/docs/for.html) has iterated through all the given elements, or if [`while`](/commands/docs/while.html)'s condition is now false, it won't loop again and execution will continue after the loop block. ```nu mut x = -1; while $x <= 6 { $x = $x + 1; if $x mod 3 == 0 { continue }; print $x } # => 1 # => 2 # => 4 # => 5 # => 7 ``` ## Errors ### `error make` [`error make`](/commands/docs/error_make.html) creates an error that stops execution of the code and any code that called it, until either it is handled by a [`try`](/commands/docs/try.html) block, or it ends the script and outputs the error message. This functionality is the same as "exceptions" in other languages. ```nu print 'printed'; error make { msg: 'Some error info' }; print 'unprinted' # => printed # => Error: × Some error info # => ╭─[entry #9:1:1] # => 1 │ print 'printed'; error make { msg: 'Some error info' }; print 'unprinted' # => · ─────┬──── # => · ╰── originates from here # => ╰──── ``` The record passed to it provides some information to the code that catches it or the resulting error message. You can find more information about [`error make`](/commands/docs/error_make.html) and error concepts on the [Creating your own errors page](/book/creating_errors.html). ### `try` [`try`](/commands/docs/try.html) will catch errors created anywhere in the [`try`](/commands/docs/try.html)'s code block and resume execution of the code after the block. ```nu try { error make { msg: 'Some error info' }}; print 'Resuming' # => Resuming ``` This includes catching built in errors. ```nu try { 1 / 0 }; print 'Resuming' # => Resuming ``` The resulting value will be `nothing` if an error occurs and the returned value of the block if an error did not occur. If you include a `catch` block after the [`try`](/commands/docs/try.html) block, it will execute the code in the `catch` block if an error occurred in the [`try`](/commands/docs/try.html) block. ```nu try { 1 / 0 } catch { 'An error happened!' } | $in ++ ' And now I am resuming.' # => An error happened! And now I am resuming. ``` It will not execute the `catch` block if an error did not occur. `try` also works for external commands: ```nu try { ^nonexisting }; print 'a' # => a ^nonexisting; print 'a' # => Error: nu::shell::external_command # => # => × External command failed # => ╭─[entry #3:1:2] # => 1 │ ^nonexisting; print 'a' # => · ─────┬───── # => · ╰── Command `nonexisting` not found # => ╰──── # => help: `nonexisting` is neither a Nushell built-in or a known external command ``` ## Other ### `return` [`return`](/commands/docs/return.html) Ends a closure or command early where it is called, without running the rest of the command/closure, and returns the given value. Not often necessary since the last value in a closure or command is also returned, but it can sometimes be convenient. ```nu def 'positive-check' [it] { if $it > 0 { return 'positive' }; 'non-positive' } ``` ```nu positive-check 3 # => positive positive-check (-3) # => non-positive let positive_check = {|elt| if $elt > 0 { return 'positive' }; 'non-positive' } do $positive_check 3 # => positive do $positive_check (-3) # => non-positive ```

This section covers error handling in Nushell using `error make` to generate errors and `try` to catch them. It also demonstrates how to use the `catch` block within `try` to handle errors. The section further explains the use of `return` to exit closures or commands early and return a value, though it's often unnecessary as the last value is returned by default.