add now whoami subcommand (#587)

Not logged in:

```
$ now whoami
> Not currently logged in! Please run `now --login`.
```

Logged in, stdout is a TTY:

```
$ now whoami
> tootallnate
$ now switch zeit
$ now whoami
> zeit
```

Stdout is NOT a TTY:

```
$ echo "Logged in to Now as $(now whoami)"
Logged in to Now as tootallnate
```

Closes #585.

bin/now-whoami.js

@@ -0,0 +1,70 @@
+#!/usr/bin/env node
+
+// Packages
+const minimist = require('minimist')
+const chalk = require('chalk')
+
+// Ours
+const cfg = require('../lib/cfg')
+const exit = require('../lib/utils/exit')
+const cmd = require('../lib/utils/output/cmd')
+const logo = require('../lib/utils/output/logo')
+
+const argv = minimist(process.argv.slice(2), {
+  string: ['config', 'token'],
+  boolean: ['help', 'debug', 'all'],
+  alias: {
+    help: 'h',
+    config: 'c',
+    debug: 'd',
+    token: 't'
+  }
+})
+
+const help = () => {
+  console.log(`
+  ${chalk.bold(`${logo} now whoami`)}
+
+  ${chalk.dim('Options:')}
+
+    -h, --help              Output usage information
+    -c ${chalk.bold.underline('FILE')}, --config=${chalk.bold.underline('FILE')}  Config file
+    -d, --debug             Debug mode [off]
+    -t ${chalk.bold.underline('TOKEN')}, --token=${chalk.bold.underline('TOKEN')} Login token
+
+  ${chalk.dim('Examples:')}
+
+  ${chalk.gray('–')} Show the current team context
+
+    ${chalk.cyan('$ now whoami')}
+`)
+}
+
+if (argv.help) {
+  help()
+  process.exit(0)
+}
+
+if (argv.config) {
+  cfg.setConfigFile(argv.config)
+}
+
+async function whoami() {
+  const config = await cfg.read({ token: argv.token })
+  if (!config || !config.token) {
+    console.log(
+      `> Not currently logged in! Please run ${cmd('now --login')}.\n`
+    )
+    return exit(1)
+  }
+
+  if (process.stdout.isTTY) {
+    process.stdout.write('> ')
+  }
+
+  const { currentTeam, user } = config
+  const name = (currentTeam && currentTeam.slug) || user.username || user.email
+  console.log(name)
+}
+
+whoami()

bin/now.js

@@ -53,7 +53,8 @@ const commands = new Set([
   'log',
   'logs',
   'scale',
-  'logout'
+  'logout',
+  'whoami'
 ])
 
 const aliases = new Map([