Many programming guides recommend to begin scripts with the #! /usr/bin/env shebang in order to to automatically locate the necessary interpreter. For example, for a Python script you would use #! /usr/bin/env python, and then the saying goes, the script would “just work” on any machine with Python installed. The reason for this recommendation is that /usr/bin/env python will search the PATH for a program called python and execute the first one found… and that usually works fine on one’s own machine.
C. Wang, and D. Blei. Proceedings of the 17th ACM SIGKDD International Conference on Knowledge Discovery and Data Mining, page 448--456. New York, NY, USA, ACM, (2011)