docs/feat: add stdin support via - filename

README.md

@@ -72,6 +72,14 @@ ical2rem [OPTION]… FILE…
 
 Output goes to stdout and can be redirected to a `.rem` file.
 
+Pass `-` as a filename to read from standard input. `-` may appear at most once,
+but can be freely mixed with regular files:
+
+```bash
+curl https://example.com/calendar.ics | ical2rem - > calendar.rem
+ical2rem work.ics - personal.ics > all.rem
+```
+
 ### Examples
 
 Convert a single calendar:
@@ -99,6 +107,11 @@ Strip all metadata lines from output:
 ical2rem --no-uuid --no-source --no-location --no-description --no-conference-url personal.ics
 ```
 
+Use stdin as input calendar:
+```bash
+curl https://example.com/calendar.ics | ical2rem - > calendar.rem
+```
+
 Override calendar name in `INFO` lines (single file only):
 ```bash
 ical2rem --source "Work" work.ics > work.rem
@@ -113,7 +126,7 @@ ical2rem --verbose personal.ics > personal.rem
 
 | Option | Description |
 |---|---|
-| `FILE…` | One or more `.ics` files to convert |
+| `FILE…` | One or more `.ics` files to convert; use `-` for standard input (at most once) |
 | `-z`, `--timezone TZ` | Target timezone for output (default: local) |
 | `--sort asc\|desc\|original` | Sort order by date (default: `desc`); `original` preserves processing order (sorted by UID within each file, last file first) |
 | `--source NAME` | Override calendar name (single file only) |

bin/main.ml

@@ -14,7 +14,22 @@ let read_file filename =
   close_in ic;
   Bytes.unsafe_to_string s
 
+let read_stdin () =
+  let buf = Buffer.create 4096 in
+  (try
+     while true do
+       Buffer.add_channel buf stdin 4096
+     done
+   with End_of_file -> ());
+  Buffer.contents buf
+
 let ical2rem (args : CommandLine.cli_args) ical_files =
+  (* Validate: '-' (stdin) may appear at most once *)
+  let stdin_count = List.length (List.filter (( = ) "-") ical_files) in
+  if stdin_count > 1 then begin
+    Printf.eprintf "Error: '-' (stdin) may appear at most once.\n";
+    exit 1
+  end;
   (* Validate --source with multiple files *)
   (match args.source with
   | Some _ when List.length ical_files > 1 ->
@@ -31,11 +46,17 @@ let ical2rem (args : CommandLine.cli_args) ical_files =
   let good_rems =
     ListLabels.fold_left ~init:[] ical_files ~f:(fun good_rems_acc filename ->
         try
-          let file_content = read_file filename in
-          let basename =
-            match args.source with
-            | Some name -> name
-            | None -> Filename.remove_extension (Filename.basename filename)
+          let file_content, basename =
+            if filename = "-" then
+              ( read_stdin (),
+                match args.source with
+                | Some name -> name
+                | None -> "stdin" )
+            else
+              ( read_file filename,
+                match args.source with
+                | Some name -> name
+                | None -> Filename.remove_extension (Filename.basename filename) )
           in
           match Icalendar.parse file_content with
           | Error e ->