Cookbook getenv\n\nRecreate PR #2383

data/cookbook/read-environment-variable/00-stdlib.ml

@@ -0,0 +1,16 @@
+---
+packages: []
+discussion: |
+  - **Understanding `Sys.getenv` and `Sys.getenv_opt`:** Both `Sys.getenv` and `Sys.getenv_opt` functions take a environment variable name and return its value. `Sys.getenv` returns directly the value, but raises a `Not_found` exception if the variable doesn't exist. `Sys.getenv_opt` returns an `option` type: `Some value` if the variable exists and `None` if not.
+---
+
+let path = Sys.getenv "PATH"
+let () =
+  Printf.printf "The path is %s\n" path
+
+let () =
+  match Sys.getenv_opt "OPAM_SWITCH_PREFIX" with
+  | Some p ->
+      Printf.printf "The Opam switch prefix is %s\n" p
+  | None ->
+      print_string "The Opam switch prefix is not set.\n"