binmode F; local $/ = undef;
$encoded = encode_base64(<F>);
close F;

The question I have, is does this local version of $/ only affect this
scope ?
I am aware that any functions I call for example within this function,
will inherit the undefined version of $/, but will this not affect the
value of $/ for other instances of the program running ?

If multiple users hit the server at the same time, and someone happens
to be executing this code, am I correct in assuming that the version
of $/ used by other users sessions will be the correct global version
and not the local one defined in the above code ?

------------------------------
#!/usr/bin/perl -w
use strict;

aaa();
print "[$/]";

sub aaa{
  local $/ = 'bla';

  print "In aaa \$/ = [$/]\n";
  bbb();

As you see the global value of $/ is untouched by the subs,
which is actually the point of using local in the first place.

        {
            binmode F;
            local $/;   # no need to assign undef
            $encoded = encode_base64(<F>);
            close F;
        }