Add examples/is_tty.clj (#812) [skip ci]

examples/README.md

@@ -31,6 +31,7 @@
   - [fzf](#fzf)
   - [digitalocean-ping.clj](#digitalocean-pingclj)
   - [download-aliases.clj](#download-aliasesclj)
+  - [Is TTY?](#is-tty)
 
 Here's a gallery of useful examples. Do you have a useful example? PR welcome!
 
@@ -431,3 +432,33 @@ $ bb digitalocean-ping.clj
 ## [download-aliases.clj](download-aliases.clj)
 
 Download deps for all aliases in a deps.edn project.
+
+## [Is TTY?](is_tty.clj)
+
+An equivalent of Python's `os.isatty()` in Babashka, to check if the
+`stdin`/`stdout`/`stderr` is connected to a TTY or not (useful to check if the
+script output is being redirect to `/dev/null`, for example).
+
+Only works in Unix systems.
+
+``` shell
+$ bb is-tty.clj
+STDIN is TTY?: true
+STDOUT is TTY?: true
+STDERR is TTY?: true
+
+$ bb is-tty.clj </dev/null
+STDIN is TTY?: false
+STDOUT is TTY?: true
+STDERR is TTY?: true
+
+$ bb is-tty.clj 1>&2 >/dev/null
+STDIN is TTY?: true
+STDOUT is TTY?: false
+STDERR is TTY?: true
+
+$ bb is-tty.clj 2>/dev/null
+STDIN is TTY?: true
+STDOUT is TTY?: true
+STDERR is TTY?: false
+```

examples/is_tty.clj

@@ -0,0 +1,21 @@
+#!/usr/bin/env bb
+
+(ns is-tty
+  (:require [babashka.process :as p]))
+
+(defn- is-tty
+  [fd key]
+  (-> ["test" "-t" (str fd)]
+      (p/process {key :inherit :env {}})
+      deref
+      :exit
+      (= 0)))
+
+(defn in-is-tty? [] (is-tty 0 :in))
+(defn out-is-tty? [] (is-tty 1 :out))
+(defn err-is-tty? [] (is-tty 2 :err))
+
+(when (= *file* (System/getProperty "babashka.file"))
+  (println "STDIN is TTY?:" (in-is-tty?))
+  (println "STDOUT is TTY?:" (out-is-tty?))
+  (println "STDERR is TTY?:" (err-is-tty?)))