use strict;
use warnings;
sub cat_all {
    my $fh = shift;
    print while <$fh>;
}

cat_all \*ARGV;
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BTW I found this by inspecting the output of perl -MData::Dumper -wle 'print Dumper [ keys %::]'. Looking at perlvar also helped.

Quoting from perlvar:

ARGV

The special filehandle that iterates over command-line filenames in @ARGV. Usually written as the null filehandle in the angle operator <> . Note that currently ARGV only has its magical effect within the <> operator; elsewhere it is just a plain filehandle corresponding to the last file opened by <>. In particular, passing \*ARGV as a parameter to a function that expects a filehandle may not cause your function to automatically read the contents of all the files in @ARGV.

So what you posted won't work. I don't know of any way reproduce the same function with a passed parameter, although I suspect a tied file handle would be the best way to do so.

It works for me; that is, (on my particular systems with the particular versions of Perl I'm using,) passing \*ARGV to a (trivial) function that expects a filehandle certainly does cause it to read the contents of all the files in @ARGV, even if I have reassigned @ARGV since the last read from <>.

So, I'm now intrigued by that "may not" there. What are the conditions where it doesn't work? Is it platform-based? version-based? phase-of-moon-based...?

update: see perlvar.

perl -e 'print while <ARGV>'
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