feat(shell): run -c strings inside a system shell (#22)

Fixes: #21

README.md

@@ -30,7 +30,9 @@ If a version specifier is included, or if `--package` is used, npx will ignore t
 
 * `--userconfig` - path to the user configuration file to pass to npm. Defaults to whatever npm's current default is.
 
-* `-c <string>` - Execute `<string>` with delayed environment variable evaluation.
+* `-c <string>` - Execute `<string>` inside a shell. For unix, this will be `/bin/sh -c <string>`. For Windows, it will be `cmd.exe /d /s /c <string>`. Only the first item in `<string>` will be automatically used as `<command>`. Any others _must_ use `-p`.
+
+* `--shell <string>` - The shell to invoke the command with, if any. Defaults to `false`.
 
 * `--shell-auto-fallback [shell]` - Generates shell code to override your shell's "command not found" handler with one that calls `npx`. Tries to figure out your shell, or you can pass its name (either `bash`, `fish`, or `zsh`) as an option. See below for how to install.
 
@@ -62,6 +64,12 @@ $ cat package.json
 ...webpack added to "devDependencies"
 ```
 
+### Execute a full shell command using one npx call
+
+```
+$ npx -p cowsay -c 'echo "foo" | cowsay'
+```
+
 ## SHELL AUTO FALLBACK
 
 To install permanently, add the relevant line to your `~/.bashrc`, `~/.zshrc`, `~/.config/fish/config.fish`, or as needed. To install just for the shell session, simply run the line.

index.js

@@ -36,7 +36,7 @@ function main (argv) {
     return getCmdPath(
       argv.command, argv.package, argv
     ).then(cmdPath => {
-      return runCommand(cmdPath, argv.cmdOpts)
+      return runCommand(cmdPath, argv.cmdOpts, argv)
     }).catch(err => {
       console.error(err.message)
       process.exit(err.exitCode || 1)
@@ -137,8 +137,9 @@ function installPackage (spec, prefix, npmOpts) {
   })
 }
 
-function runCommand (cmdPath, cmdOpts) {
+function runCommand (cmdPath, cmdOpts, opts) {
   return spawn(cmdPath, cmdOpts, {
+    shell: opts.shell || !!opts.call,
     stdio: 'inherit'
   }).catch({code: 'ENOENT'}, () => {
     throw new Error(`npx: command not found: ${path.basename(cmdPath)}`)

parse-args.js

@@ -62,6 +62,12 @@ function parseArgs () {
     type: 'string',
     describe: 'execute string as if inside `npm run-script`'
   })
+  .option('shell', {
+    alias: 's',
+    type: 'string',
+    describe: 'Shell to execute the command with, if any.',
+    default: false
+  })
   .option('shell-auto-fallback', {
     choices: ['', 'bash', 'fish', 'zsh'],
     describe: 'generate shell code to use npx as the "command not found" fallback',