auto-mode-interpreter-regexp is a variable defined in `files.el'.
Its value is
"#![ 	]?\\([^ 	
]*/bin/env[ 	]\\)?\\([^ 	

Regexp matching interpreters, for file mode determination.
This regular expression is matched against the first line of a file
to determine the file's mode in `set-auto-mode'. If it matches, the file
is assumed to be interpreted by the interpreter matched by the second group
of the regular expression. The mode is then determined as the mode
associated with that interpreter in `interpreter-mode-alist'.