Brad Lucas

Programming, Clojure and other interests
September 29, 2017

Clojure And STDERR

How to print to STDERR in Clojure came up the other day.

It turns out there are two vars *out* and *err* that are bound to STDOUT and STDERR. There vars are instances of `java.io.PrintWriter' and you can simply write to them.

For example, here is a string being printed to STDOUT.

user> (.println *out* "hello")
hello
nil

The same can be done for STDERR. Just send a string out through *err*.

 (.println *out* "hello")
hello
nil

In addition you can also send something to *err* by temporarily binding the value of *out* to the current value of *err*. This allows you use your normal println function and have it's output go to a different place.

  (binding [*out* *err*]
    (println msg))

The repo linked below has a simple Clojure project you can build and run to show both techniques.


Tags: clojure