Parsing Tricks

Stop Parsing

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Use -- to stop parsing flags and stuff the remainder into argv._.

$ node examples/reflect.js -a 1 -b 2 -- -c 3 -d 4
{ _: [ '-c', '3', '-d', '4' ],
  a: 1,
  b: 2,
  '$0': 'examples/reflect.js' }

Negating Boolean Arguments

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If you want to explicitly set a field to false instead of just leaving it undefined or to override a default you can do --no-key.

$ node examples/reflect.js -a --no-b
{ _: [], a: true, b: false, '$0': 'examples/reflect.js' }

Numbers

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Every argument that looks like a number (!isNaN(Number(arg))) is converted to one. This way you can just net.createConnection(argv.port) and you can add numbers out of argv with + without having that mean concatenation, which is super frustrating.

You can change this behavior by calling parserConfiguration() or by explicitly specifying string for your flags.

Arrays

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If you specify a flag multiple times it will get turned into an array containing all the values in order.

$ node examples/reflect.js -x 5 -x 8 -x 0
{ _: [], x: [ 5, 8, 0 ], '$0': 'examples/reflect.js' }

You can also configure an option as the type array, to support arrays of the form -x 5 6 7 8.

Objects

---

When you use dots (.s) in argument names, an implicit object path is assumed. This lets you organize arguments into nested objects.

$ node examples/reflect.js --foo.bar.baz=33 --foo.quux=5
{ _: [],
  foo: { bar: { baz: 33 }, quux: 5 },
  '$0': 'examples/reflect.js' }

Quotes

When you use string arguments that include dashes (-), those will be seen as a separate option by the shell instead of part of the string. The problem is that shells like bash tend to strip quotes. The solution for this is to wrap the string in two sets of quotes.

Use double quotes inside single quotes.

$ node examples/reflect.js --foo '"--hello -x=yes -v"'
{ _: [], foo: '--hello -x=yes -v',
  '$0': 'examples/reflect.js' }

Use escaped double quotes inside double quotes.

$ node examples/reflect.js --foo "\"--hello -x=yes -v\""
{ _: [], foo: '--hello -x=yes -v',
  '$0': 'examples/reflect.js' }