When MzScheme is installed as part of the standard Unix PLT
distribution, the executable ${PLTHOME}/bin/mzscheme is actually a
script that selects an executable based on the current platform. This
is done to support multiple platforms in a single PLT installation.

Unfortunately, this causes problems for writing scripts that use
MzScheme, because the shell's #! convention requires that a binary is
specified.

Fortunately, there is a sneaky workaround. To write a MzScheme script,
use the following at the top of your script:

  #!/bin/sh
  string=? ; exec ${PLTHOME}/bin/mzscheme -r $0 $0 ${1+"$@"}

  ... <scheme program> ...

(It may be better to hardwire the path to mzscheme instead of using
${PLTHOME}.)

Within <scheme program>, (vector-ref argv 0) is the name of the
script; arguments passed to the script start at (vector-ref argv 1).

How does this work? "#!/bin/sh" causes the shell to run /bin/sh on the
file. The first command, "string=?" is a harmless assignment, and ";"
separates this assignment from the "exec" command. The "exec" command
replaces /bin/sh with mzscheme (so /bin/sh does not see the actual
Scheme program). The "-r" flag tells mzscheme to load the next
argument as a script and forces the remaining arguments into
`argv'. (For information on ${1+"$@"}, consult your `sh' man page.)
Thus, mzscheme will start up and load this file. As always, mzscheme
ignores "#!" in the first line of a loaded file as a comment. And
"string=?" is again a harmless expression (since it's a built-in
variable). The ";" starts a Scheme comment, so the "exec" expression
is ignored. Finally, mzscheme continues to load the file and evaluates
the real Scheme program.

Thanks to J. P. Lewis <zilla@interval.com> for the basic idea behind
this trick. Many others have suggested alternatives to `string=?'
for shells other than /bin/sh.