Thanks -- those are very helpful links. I found out from reading those that using the PERLIO environment variable does in fact provide the desired effect. For example, this script: 
#!/usr/bin/perl -w

binmode STDOUT, ":encoding(utf16)";

while (<>) {
    print;
}

[download]
will correctly convert utf8 input to utf16 output, whether reading from STDIN or a list of one or more files in @ARGV, when I run it like this: 
$ export PERLIO=:utf8
$ myscript *.utf8
## works the same as:  cat *.utf8 | myscript

[download]
Alas, if I just put  $ENV{PERLIO} = ":utf8"; into the script itself, this doesn't work. So to really free my script from undesirable environment dependencies, I could just make a wrapper script that sets $ENV{PERLIO}, then execs the actual filter script with @ARGV. Not exactly pretty, but not as ugly as other alternatives.

In reply to Re^2: Using binmode on ARGV filehandle? (open.pm) by graff
in thread Using binmode on ARGV filehandle? by graff

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