From 5e8771e77b5163efcaa7b6effe66712d9184cb48 Mon Sep 17 00:00:00 2001
From: Mark van Seventer <mark@vseventer.com>
Date: Mon, 24 Aug 2026 07:21:22 -0700
Subject: [PATCH 1/2] Fixes #49.

---
 CHANGELOG.md                |  4 ++++
 cmd/resizing/resize.js      | 32 ++++++++++++++++++++++++++------
 package.json                |  2 +-
 test/cmd/resizing/resize.js | 24 ++++++++++++++++++++----
 4 files changed, 51 insertions(+), 11 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 15f620c..3f70990 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Changelog
 
+## 6.1.0-dev
+
+- Added percentage-based dimensions to the `resize` command ([#49](https://github.com/vseventer/sharp-cli/issues/49)).
+
 ## 6.0.0 (August 21, 2026)
 
 - Added [`--limitInputChannels`](https://sharp.pixelplumbing.com/api-constructor/) input option.
diff --git a/cmd/resizing/resize.js b/cmd/resizing/resize.js
index d9520dc..ee94331 100644
--- a/cmd/resizing/resize.js
+++ b/cmd/resizing/resize.js
@@ -27,17 +27,31 @@
 import constants from "../../lib/constants.js";
 import { pick } from "../../lib/utils.js";
 
+// Helpers.
+const resolveDimension = (dimension, metadataDimension) => {
+  if (dimension == null) return null;
+  if (typeof dimension === "string" && dimension.endsWith("%")) {
+    if (metadataDimension == null) {
+      throw new Error("Input metadata is required to resolve percentage");
+    }
+    return Math.round(
+      (metadataDimension * Number(dimension.slice(0, -1))) / 100,
+    );
+  }
+  return Number(dimension);
+};
+
 // Configure.
 const positionals = {
   width: {
     default: null,
-    desc: "Pixels wide the resultant image should be",
-    type: "number",
+    desc: "Pixels or percentage wide the resultant image should be",
+    type: "string",
   },
   height: {
     default: null,
-    desc: "Pixels high the resultant image should be",
-    type: "number",
+    desc: "Pixels or percentage high the resultant image should be",
+    type: "string",
   },
 };
 
@@ -94,6 +108,10 @@ const builder = (yargs) => {
       "$0 resize --height 100",
       "The output will be 100 pixels high, auto-scaled width",
     )
+    .example(
+      "$0 resize 50%",
+      "The output will be 50% of the input width, auto-scaled height",
+    )
     .example(
       '$0 resize 200 300 --background rgba(255,255,255,0.5) --fit contain --kernel nearest --position "right top"',
       "The output will be 200 pixels wide and 300 pixels high containing a nearest-neighbour scaled version contained within the north-east corner of a semi-transparent white canvas",
@@ -132,8 +150,10 @@ const handler = (args) => {
   // @see https://sharp.pixelplumbing.com/api-resize#resize
   return args["#queue"].push([
     "resize",
-    (sharp) => {
-      return sharp.resize(args.width, args.height, pick(args, optionNames));
+    (sharp, { metadata } = {}) => {
+      const width = resolveDimension(args.width, metadata?.width);
+      const height = resolveDimension(args.height, metadata?.height);
+      return sharp.resize(width, height, pick(args, optionNames));
     },
   ]);
 };
diff --git a/package.json b/package.json
index 0f1aa0b..656ed29 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "sharp-cli",
-  "version": "6.0.0",
+  "version": "6.1.0-dev",
   "description": "CLI for sharp.",
   "keywords": [
     "cli",
diff --git a/test/cmd/resizing/resize.js b/test/cmd/resizing/resize.js
index a84c093..c1b8bd1 100644
--- a/test/cmd/resizing/resize.js
+++ b/test/cmd/resizing/resize.js
@@ -62,7 +62,7 @@ export default function register() {
 
       it("must set the width flag", () => {
         const args = cli.parsed.argv;
-        assert.equal(args["width"], width);
+        assert.equal(args["width"], String(width));
       });
       it("must update the pipeline", () => {
         const pipeline = getPipeline(cli.parsed.argv);
@@ -80,7 +80,7 @@ export default function register() {
 
       it("must set the height flag", () => {
         const args = cli.parsed.argv;
-        assert.equal(args["height"], height);
+        assert.equal(args["height"], String(height));
       });
       it("must update the pipeline", () => {
         const pipeline = getPipeline(cli.parsed.argv);
@@ -100,8 +100,8 @@ export default function register() {
       // Tests.
       it("must set the width and height flags", () => {
         const args = cli.parsed.argv;
-        assert.equal(args["width"], width);
-        assert.equal(args["height"], height);
+        assert.equal(args["width"], String(width));
+        assert.equal(args["height"], String(height));
       });
       it("must update the pipeline", () => {
         const pipeline = getPipeline(cli.parsed.argv);
@@ -114,6 +114,22 @@ export default function register() {
       });
     });
 
+    describe("percentage dimensions", () => {
+      const metadata = { height: 331, width: 500 };
+
+      it("must resize width relative to input metadata", async () => {
+        await cli.parseAsync(["resize", "50%"]);
+        const pipeline = drain(cli.parsed.argv, { metadata });
+        sinon.assert.calledWithMatch(pipeline.resize, 250, null);
+      });
+
+      it("must resize width and height relative to input metadata", async () => {
+        await cli.parseAsync(["resize", "50%", "75%"]);
+        const pipeline = drain(cli.parsed.argv, { metadata });
+        sinon.assert.calledWithMatch(pipeline.resize, 250, 248);
+      });
+    });
+
     describe("[options]", () => {
       // @see https://sharp.pixelplumbing.com/api-resize#resize
       describe("--background", () => {

From c72309e88aa3e94ffd038fb5cca48f4b9be9814d Mon Sep 17 00:00:00 2001
From: Mark van Seventer <mark@vseventer.com>
Date: Tue, 25 Aug 2026 08:08:50 -0700
Subject: [PATCH 2/2] Add test.

---
 test/cmd/resizing/resize.js | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/test/cmd/resizing/resize.js b/test/cmd/resizing/resize.js
index c1b8bd1..a6677c1 100644
--- a/test/cmd/resizing/resize.js
+++ b/test/cmd/resizing/resize.js
@@ -128,6 +128,14 @@ export default function register() {
         const pipeline = drain(cli.parsed.argv, { metadata });
         sinon.assert.calledWithMatch(pipeline.resize, 250, 248);
       });
+
+      it("must fail when input metadata is not set", async () => {
+        await cli.parseAsync(["resize", "50%"]);
+        assert.throws(
+          () => drain(cli.parsed.argv),
+          "metadata is required to resolve percentage",
+        );
+      });
     });
 
     describe("[options]", () => {