Add 'bash/booleans.bash'

bash/booleans.bash

@@ -0,0 +1,23 @@
+#!/bin/bash
+
+# BASH doesn't actually understand booleans.
+# What you can do however is to trick it by using the fact that the true and false commands return 0 and 1,
+# so it can stand in for boolean algebra if used correctly.
+
+BOOLEAN1=false
+
+if $BOOLEAN1; then
+    echo "We won't get here because BOOLEAN1 is false."
+fi
+if ! $BOOLEAN1; then
+    echo "But we DO get here."
+fi
+
+BOOLEAN1=true
+
+if $BOOLEAN1; then
+    echo "Now we do get in this as it's been set to true."
+fi
+if ! $BOOLEAN1; then
+    echo "And now we DON'T get here."
+fi