Thanks for the suggestion, though I solved my actual problem per the response below (localizing $. wherever my module performed a seek() or used <>).

Instead of using IO::File as you propose, since open()'ed files are automatically IO::Handles, you can just "use IO::Handle;" to provide the input_line_number method (note the continue):

use strict;
use warnings;
use IO::Handle;

while (<>) {
    my $lineno = ARGV->input_line_number;
    # print a status message every 100 lines
    warn "Processing $ARGV line $lineno\n" unless $lineno % 100;
    # do some processing stuff
} continue {
    close ARGV if ARGV->eof; # else input_line_number won't reset per-
+file
}
[download]

(Update:) s/eof/ARGV->eof/ in the code example. (else a poorly written function, like my original seeky() would let the eof refer to the wrong file)