The GAWK Manual
The `#!' mechanism works on
Unix systems derived from Berkeley Unix, System V Release 4, and some System
V Release 3 systems.
The
line beginning with `#!' lists the full pathname of an interpreter
to be run, and an optional initial command line argument to pass to that
interpreter. The operating system then runs the interpreter with the given
argument and the full argument list of the executed program. The first argument
in the list is the full pathname of the awk program. The rest of the
argument list will either be options to awk, or data files,
or both.
Since
all variables in awk are global, this program uses the common
practice of prefixing the variable name with an underscore. In fact, it
also suffixes the variable name with an underscore, as extra insurance
against using a variable name that might be used in some other library
file.