Under UNIX, to my knowledge, any regular file can be made executable with the addition of a shebang:
#! /path/to/executing-program --with --options
How can I apply the same principle to a TeX file without altering syntax rules for the entire document?
$ cat > tmp.tex
#! /usr/bin/env tex --mystery --options
hello, world
\bye
$ chmod +x tmp.tex
$ ./tmp.tex
$ dvi2tty -q tmp.dvi | grep .
hello, world
1
$ logout