#!/usr/bin/perl -w

# Arguments are file names; tags all nonblank lines with filename,
# colon, line number, and colon.  Passes blank lines through
# untouched.  Omits file name if only one argument.

$numfiles = @ARGV;
while (<>) {
    print "$ARGV" if ($numfiles>1);
    print ":$.:" if ! /^$/;
    print;
    close(ARGV) if eof;
}