Read markdown from standard input when the filename is -

CLAUDE.md

@@ -31,7 +31,7 @@ Requires Go (see `go.mod`/`mise.toml` for version) and, for packaging, `just`, `
 
 Everything happens in `main()` in `main.go`, in a straight-line pipeline:
 
-1. **Flag parsing** — `-o`, `-v/-version`, `-h/-help`, `-b/-bare`. First positional arg is the input markdown file.
+1. **Flag parsing** — `-o`, `-v/-version`, `-h/-help`, `-b/-bare`. First positional arg is the input markdown file; a single `-` reads the markdown from stdin instead, in which case `baseDir` for image resolution is the working directory rather than the input file's directory.
 2. **Image inlining** (`processMarkdownImages` → `processHTMLImages`/markdown image regex + `imageToDataURI`) — rewrites relative image references (both `![]()`  markdown syntax and raw `<img src=...>` HTML) into base64 `data:` URIs *before* markdown parsing, so the output HTML is fully self-contained/offline-viewable. This includes path-traversal guards (caps `..` traversal depth) and a 10MB per-image size cap.
 3. **Markdown parsing** via Goldmark, configured with:
    - `extension.GFM` (tables, task lists, strikethrough, etc.)

README.md

@@ -19,6 +19,19 @@ A lightweight command-line tool that converts markdown files to styled HTML and
 
 ## Usage
 
+Pass a filename, or a single dash to read markdown from standard input:
+
+```sh
+mdview notes.md
+cat notes.md | mdview -
+age -d -i ~/.config/age/key.txt notes.md.age | mdview -
+```
+
+Reading from standard input avoids writing the markdown to disk first,
+which is useful when the content is decrypted or generated on the fly.
+Relative image paths are then resolved against the current working
+directory.
+
 By default, `mdview` writes the generated HTML to a temporary directory.
 It tries these in order:
 - A path defined in the `MDVIEW_DIR` environment variable

main.go

@@ -9,6 +9,7 @@ import (
 	"errors"
 	"flag"
 	"fmt"
+	"io"
 	"io/fs"
 	"log"
 	"os"
@@ -59,16 +60,28 @@ func main() {
 	}
 
 	if inputFilename == "" || *helpPtr {
-		os.Stderr.WriteString("Usage:\nmdview [options] <filename>\nFormats markdown and launches it in a browser.\nIf the environment variable MDVIEW_DIR is set, the temporary file will be written there.\n")
+		os.Stderr.WriteString("Usage:\nmdview [options] <filename>\nFormats markdown and launches it in a browser.\nUse - as the filename to read markdown from standard input.\nIf the environment variable MDVIEW_DIR is set, the temporary file will be written there.\n")
 		flag.PrintDefaults()
 		os.Exit(1)
 	}
 
-	dat, err := os.ReadFile(inputFilename)
-	check(err)
+	// A filename of - means read the markdown from standard input. Relative image
+	// paths are then resolved against the working directory, as there is no input
+	// file to anchor them to.
+	var dat []byte
+	var err error
+	baseDir := "."
+
+	if inputFilename == "-" {
+		dat, err = io.ReadAll(os.Stdin)
+		check(err)
+	} else {
+		dat, err = os.ReadFile(inputFilename)
+		check(err)
+		baseDir = filepath.Dir(inputFilename)
+	}
 
 	// Convert relative image links to data URIs in the markdown source
-	baseDir := filepath.Dir(inputFilename)
 	processedMarkdown := processMarkdownImages(string(dat), baseDir)
 	processedBytes := []byte(processedMarkdown)
 

mdview.1.md

@@ -7,6 +7,7 @@
 # SYNOPSIS
 
 **mdview** _filename_  
+**mdview** **-**  
 **mdview** \[**-h**|**--help**|**-v**|**--version**]
 
 # DESCRIPTION
@@ -16,6 +17,10 @@ then launches that file in the default web browser. By default, it will
 use the operating system's default temporary directory unless the
 environment variable MDVIEW_DIR is set.
 
+If _filename_ is a single dash (**-**), the markdown is read from
+standard input. Relative image paths are then resolved against the
+current working directory.
+
 ## Options
 
 **-b**, **-bare**