Sonatype does not as yet publish an official stand-alone command line tool for administering Nexus.
Sonatype publishes official tool integrations, for tooling such as Apache Maven and Apache Ant.
Some third-parties have created some stand alone tools and APIs you might find useful.
Third-Party Sonatype Nexus Command Line Tools
Contact the project author should you have an issue with a specific tool.
Sonatype maintains a curated list of integrations for Nexus Repository Manager at