Create some files

src/inputs/index.ts

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+import { getInput, InputOptions } from '@actions/core'
+
+export interface Inputs {
+  readonly version: string
+  readonly dest: string
+  readonly binDest: string
+  readonly registry: string
+}
+
+const options: InputOptions = {
+  required: true,
+}
+
+export const getInputs = (): Inputs => ({
+  version: getInput('version', options),
+  dest: getInput('dest', options),
+  binDest: getInput('bin_dest', options),
+  registry: getInput('registry', options),
+})
+
+export default getInputs

src/install/index.ts

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+import { setFailed } from '@actions/core'
+import { getInputs } from '../inputs'
+import runSelfInstaller from './run'
+
+export { runSelfInstaller }
+
+export async function install() {
+  const { error, status } = await runSelfInstaller(getInputs())
+
+  if (error) return setFailed(error)
+
+  if (status) {
+    return setFailed(`Something does wrong, self-installer exits with code ${status}`)
+  }
+}
+
+export default install

src/install/run.ts

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+import { spawnSync } from 'child_process'
+import { downloadSelfInstaller } from '../self-installer'
+import { Inputs } from '../inputs'
+
+export async function runSelfInstaller(inputs: Inputs) {
+  return spawnSync('node', {
+    env: {
+      PNPM_VERSION: inputs.version,
+      PNPM_DEST: inputs.dest,
+      PNPM_BIN_DEST: inputs.binDest,
+      PNPM_REGISTRY: inputs.registry,
+    },
+    input: await downloadSelfInstaller(),
+    stdio: 'inherit',
+  })
+}
+
+export default runSelfInstaller

src/self-installer/download.ts

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+import download from 'download'
+import url from './url'
+export const downloadSelfInstaller = () => download(url)
+export default downloadSelfInstaller

src/self-installer/index.ts

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+export * from './url'
+export * from './download'

src/self-installer/url.ts

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+export const ref = '301414cec74a2b6b63c95b42f2ad1790ccb980ed'
+export const url = `https://raw.githubusercontent.com/pnpm/self-installer/${ref}/install.js`
+export default url