Tips and Tricks

Parsing Numbers

When an input is numeric, you can use Clojure's parse-long function to parse a number; it returns nil if the string is not a number. You can then check using some? within :validate:

(defcommand kill-port
  "Kills the listening process locking a port."
  [force ["-f" "--force" "Kill process without asking for confirmation"]
   :args
   port ["PORT" "Port number to kill"
         :parse-fn parse-long
         :validate [some? "Not a number"
                    pos? "Must be at least 1"]]]
  ...)                    

This handles invalid input gracefully:

> flow kill-port abc
Error in flow kill-port: PORT: Not a number

You might be tempted to use #(Long/parseLong %) as the parse function; this works, but the message produced comes from the message of the thrown exception, and is not very friendly:

> flow kill-port abc
Error in flow kill-port: PORT: Error in PORT: For input string: "abc"

Colors

You can add the namespace net.lewisship.cli-tools.colors to add a colors command.

This is a useful way to preview all the basic colors available.