babashka/doc/io-flags.md

Input and output flags

In one-liners the *input* value may come in handy. It contains the input read from stdin as EDN by default. If you want to read in text, use the -i flag, which binds *input* to a lazy seq of lines of text. If you want to read multiple EDN values, use the -I flag. The -o option prints the result as lines of text. The -O option prints the result as lines of EDN values.

Note: *input* is only available in the user namespace, designed for one-liners. For writing scripts, see scripts.

The following table illustrates the combination of options for commands of the form

echo "{{Input}}" | bb {{Input flags}} {{Output flags}} "*input*"

Input	Input flags	Output flag	*input*	Output
{:a 1} {:a 2}			{:a 1}	{:a 1}
hello bye	-i		("hello" "bye")	("hello" "bye")
hello bye	-i	-o	("hello" "bye")	hello bye
{:a 1} {:a 2}	-I		({:a 1} {:a 2})	({:a 1} {:a 2})
{:a 1} {:a 2}	-I	-O	({:a 1} {:a 2})	{:a 1} {:a 2}

When combined with the --stream option, the expression is executed for each value in the input:

$ echo '{:a 1} {:a 2}' | bb --stream '*input*'
{:a 1}
{:a 2}

Scripts

When writing scripts instead of one-liners on the command line, it is not recommended to use *input*. Here is how you can rewrite to standard Clojure code.

EDN input

Reading a single EDN value from stdin:

(ns script
 (:require [clojure.edn :as edn]))

(edn/read *in*)

Reading multiple EDN values from stdin (the -I flag):

(ns script
 (:require [clojure.edn :as edn]
           [clojure.java.io :as io]))

(let [reader  (java.io.PushbackReader. (io/reader *in*))]
  (take-while #(not (identical? ::eof %)) (repeatedly #(edn/read {:eof ::eof} reader))))

Text input

Reading text from stdin can be done with (slurp *in*). To get a lazy seq of lines (the -i flag), you can use:

(ns script
 (:require [clojure.java.io :as io]))

(line-seq (io/reader *in*))

Output

To print to stdout, use println for text and prn for EDN values.