Cookbook recipe to parse command-line arguments with Cmdliner

Author: boechat107

data/cookbook/parse-command-line-arguments/01-cmdliner.ml

@@ -0,0 +1,78 @@
+---
+packages:
+- name: cmdliner
+  tested_version: "1.3.0"
+  used_libraries:
+  - cmdliner
+---
+(* In this example, we define a parser for a command-line like this:
+
+   ```
+   mycmd --verbose input_file -o output_file
+   ```
+
+   `--verbose` and `-o` are optional, and the command should accept multiple
+   input files.
+
+   We can find more examples on
+   [this page](https://erratique.ch/software/cmdliner/doc/examples.html).
+ *)
+let cmdliner_parser () =
+  (* `Cmdliner` is a library that allows the declarative definition of
+     command-line interfaces
+     ([documentation page](https://erratique.ch/software/cmdliner/doc/index.html)).
+   *)
+  let open Cmdliner in
+  (* First we declare the expected arguments of our command-line, and how
+     `Cmdliner` should parse them. *)
+  let verbose =
+    let doc = "Output debug information" in
+    (* `&` is a right associative composition operator
+       ([documentation](https://erratique.ch/software/cmdliner/doc/Cmdliner/Arg/index.html#val-(&))).
+     *)
+    Arg.(value & flag & info ["v" ; "verbose"] ~doc)
+  and input_files =
+    let doc = "Input file(s)" in
+    Arg.(non_empty & pos_all file []
+         & info [] ~docv:"INPUT" ~doc)
+  and output_file =
+    let doc = "Output file"
+    and docv = "OUTPUT" in
+    Arg.(value & opt (some string) None
+         & info ["o"] ~docv ~doc)
+  (* `mycmd` is the function that the program will apply to the parsed
+     arguments. *)
+  and mycmd verbose input_files output_file =
+    Printf.printf "verbose: %b\n" verbose;
+    Printf.printf "input files: %s\n"
+      (input_files |> String.concat ", ");
+    Printf.printf "output file: %s\n"
+      (Option.value ~default:"" output_file)
+  in
+  (* Declaration of the complete command, including its man-like
+     documentation. *)
+  let cmd =
+    let doc = "An example command"
+    and man = [
+        `S Manpage.s_description;
+        `P "A command that can take multiple files
+            and outputs a file (optional)."
+      ]
+    in
+    Cmd.v (Cmd.info "mycmd" ~doc ~man)
+      Term.(const mycmd $ verbose $ input_files $ output_file)
+  in
+  Cmd.eval cmd
+
+
+(* Given a command-line like
+   `mycmd --verbose -o somefile ./dune-project ./cmd_cookbook.opam`, we should
+   expect the following output:
+
+   ```
+   verbose: true
+   input files: ./dune-project, ./cmd_cookbook.opam
+   output file: somefile
+   ``` *)
+let () =
+  exit @@ cmdliner_parser ()