diff --git a/README.md b/README.md
index 75ff36e..69a7b2c 100644
--- a/README.md
+++ b/README.md
@@ -152,9 +152,8 @@ HTML notebook that will be saved to the same directory with the extension
 docker run --rm \
     --env-file .env \
     -v $(pwd)/notebooks:/data \
-    -e RENDER_INPUT="/data/examples/notebook.Rmd" \
-    tschaffter/rstudio \
-    render
+    tschaffter/rstudio:4.0.5 \
+    render /data/examples/notebook.Rmd
 ```
 
 ## Versioning
diff --git a/root/render.R b/root/render.R
index 2982992..89a9f0d 100644
--- a/root/render.R
+++ b/root/render.R
@@ -1,10 +1,14 @@
-# Renders a notebook in HTML or PDF format using args specified as environment
-# variables.
+# Render an Rmd notebook to HTML or PDF.
+#
+# TODO: Use a library for managing command-line options.
 
-input = Sys.getenv("RENDER_INPUT", unset = NA)
+# input = Sys.getenv("RENDER_INPUT", unset = NA)
 output_format = Sys.getenv("RENDER_OUTPUT_FORMAT", unset = "html_document")
 quiet = Sys.getenv("RENDER_QUIET", unset = "TRUE")
 
+options <- commandArgs(trailingOnly = TRUE)
+input <- options[1]
+
 if (is.na(input)) {
   stop("The environment variable RENDER_INPUT is required")
 }
diff --git a/root/usr/local/bin/render b/root/usr/local/bin/render
index b05db99..e69884b 100755
--- a/root/usr/local/bin/render
+++ b/root/usr/local/bin/render
@@ -1,5 +1,7 @@
 #!/bin/bash
+#
+# Render an Rmd notebook to HTML or PDF.
 
 set -euo pipefail
 
-Rscript /render.R
\ No newline at end of file
+Rscript /render.R "$@"
\ No newline at end of file