Restrict script-shell to yarn run

src/cli/commands/run.js

@@ -79,7 +79,8 @@ export async function run(config: Config, reporter: Reporter, flags: Object, arg
       for (const [stage, cmd] of cmds) {
         // only tack on trailing arguments for default script, ignore for pre and post - #1595
         const cmdWithArgs = stage === action ? sh`${unquoted(cmd)} ${args}` : cmd;
-        await execCommand(stage, config, cmdWithArgs, config.cwd);
+        const customShell = config.getOption('script-shell');
+        await execCommand(stage, config, cmdWithArgs, config.cwd, customShell ? String(customShell) : undefined);
       }
     } else if (action === 'env') {
       reporter.log(JSON.stringify(await makeEnv('env', config.cwd, config), null, 2), {force: true});

src/util/execute-lifecycle-script.js

@@ -171,6 +171,7 @@ export async function executeLifecycleScript(
   cwd: string,
   cmd: string,
   spinner?: ReporterSpinner,
+  customShell?: string,
 ): LifecycleReturn {
   // if we don't have a spinner then pipe everything to the terminal
   const stdio = spinner ? undefined : 'inherit';
@@ -183,7 +184,6 @@ export async function executeLifecycleScript(
   let sh = 'sh';
   let shFlag = '-c';
 
-  const customShell = config.getOption('script-shell');
   let windowsVerbatimArguments = undefined;
 
   if (customShell) {
@@ -271,11 +271,17 @@ export async function execFromManifest(config: Config, commandName: string, cwd:
   }
 }
 
-export async function execCommand(stage: string, config: Config, cmd: string, cwd: string): Promise<void> {
+export async function execCommand(
+  stage: string,
+  config: Config,
+  cmd: string,
+  cwd: string,
+  customShell?: string,
+): Promise<void> {
   const {reporter} = config;
   try {
     reporter.command(cmd);
-    await executeLifecycleScript(stage, config, cwd, cmd);
+    await executeLifecycleScript(stage, config, cwd, cmd, undefined, customShell);
     return Promise.resolve();
   } catch (err) {
     if (err instanceof ProcessTermError) {