use Errno;

...

my %skater_avg = map
{
    chomp;
    my( $skater, @scores ) = split /,/;
    { $skater => ( sum(@scores)-min(@scores)-max(@scores) ) / (@scores-2) }
}
<>;
warn "custom message!\n" if $!{ENOENT};

##</code><code>##

use Errno;

$SIG{__WARN__} = sub {
    if ( $!{ENOENT} ) {
        warn "custom message!\n";
    }
};

##</code><code>##

( my %skater_avg = map
{
    chomp;
    my( $skater, @scores ) = split /,/;
    { $skater => ( sum(@scores)-min(@scores)-max(@scores) ) / (@scores-2) }
}
<> ) || warn "custom message!\n";