How to you specify alternative shell environments (shebangs)?

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http://unix.stackexchange.com – In an executable file, you specify the environment using a shebang: #!/usr/bin/env ruby # ruby code here But what if you want to specify multiple possible environments? For example, if you have multiple versions of Ruby installed, you may want to do something like #!/path/to/better/ruby/version #!/path/to/alternative/ruby/version # ruby code here How can you specify multiple possible environments for a single executable file? (HowTos)