allow to pipe in data to the CLI

src/cli.js

@@ -50,6 +50,21 @@ async function outputFile(file, contents) {
   await fs.promises.writeFile(file, contents, 'utf8')
 }
 
+function drainStdin() {
+  return new Promise((resolve, reject) => {
+    let result = ''
+    process.stdin.on('readable', () => {
+      let chunk
+      while ((chunk = process.stdin.read()) !== null) {
+        result += chunk
+      }
+    })
+
+    process.stdin.on('end', () => resolve(result))
+    process.stdin.on('error', (err) => reject(err))
+  })
+}
+
 function help({ message, usage, commands, options }) {
   let indent = 2
 
@@ -558,9 +573,21 @@ async function build() {
         })
     }
 
-    let css = input
-      ? fs.readFileSync(path.resolve(input), 'utf8')
-      : '@tailwind base; @tailwind components; @tailwind utilities'
+    let css = await (async () => {
+      // Input file has been provided
+      if (input) {
+        fs.readFileSync(path.resolve(input), 'utf8')
+      }
+
+      // Piping in data, let's drain the stdin
+      if (!process.stdin.isTTY) {
+        return await drainStdin()
+      }
+
+      // No input file provided, fallback to default atrules
+      return '@tailwind base; @tailwind components; @tailwind utilities'
+    })()
+
     return processCSS(css)
   }
 
@@ -694,9 +721,21 @@ async function build() {
           })
       }
 
-      let css = input
-        ? fs.readFileSync(path.resolve(input), 'utf8')
-        : '@tailwind base; @tailwind components; @tailwind utilities'
+      let css = await (async () => {
+        // Input file has been provided
+        if (input) {
+          fs.readFileSync(path.resolve(input), 'utf8')
+        }
+
+        // Piping in data, let's drain the stdin
+        if (!process.stdin.isTTY) {
+          return await drainStdin()
+        }
+
+        // No input file provided, fallback to default atrules
+        return '@tailwind base; @tailwind components; @tailwind utilities'
+      })()
+
       let result = await processCSS(css)
       env.DEBUG && console.timeEnd('Finished in')
       return result