Can multiple registries be set up in a single npmrc file?

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Yes, multiple registries can be set up in a single npmrc file. They can be defined by adding lines in the following format:

registry=https://registry.npmjs.org/
@mycompany:registry=https://npm.pkg.github.com/

In this example, the first line sets the default registry to npmjs.org, while the second line sets a scoped registry for packages from the organization "mycompany" to the GitHub package registry.