add information about switches (#1182)

* add information about switches * Update book/custom_commands.md Co-authored-by: Antoine Stevan <[email protected]> --------- Co-authored-by: Antoine Stevan <[email protected]>
nushell · Dec 21, 2023 · e4d6203 · e4d6203
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diff --git a/book/custom_commands.md b/book/custom_commands.md
@@ -292,6 +292,25 @@ Or just without the switch flag:
 > greet -a 10 hello
 ```
 
+You can also assign it to true/false to enable/disable the flag too:
+
+```nu
+> greet -a 10 --switch=false
+> greet -a 10 --switch=true
+```
+
+But note that this is not the behavior you want: `> greet -a 10 --switch false`, here the value `false` will pass as a positional argument.
+
+To avoid confusion, it's not allowed to annotate a boolean type on a flag:
+
+```nu
+def greet [
+    --twice: bool   # Not allowed
+] { ... }
+```
+
+instead, you should define it as a basic switch: `def greet [--twice] { ... }`
+
 Flags can contain dashes. They can be accessed by replacing the dash with an underscore:
 
 ```nu