sub trim {
    @_ = @_ ? @_ : $_ if defined wantarray; # disconnect aliases in non-void context

    for (@_ ? @_ : $_) { s/\A\s+//; s/\s+\z// }

    return wantarray ? @_ : "@_";
}

##</code><code>##

foreach (@args) { 
    <...>; 
    trim; 
    <...>;
}

##</code><code>##

foreach (@args) {
    my @b;
    <...>
    @b = ();
    trim(@b); # silently the same as trim($_) since @b has no elements
    <...>;
}

##</code><code>##

sub trim {
    if ( !@_ && !defined(wantarray) ) { carp 'Useless use of trim with no arguments in void return context (did you mean "trim($_)"?)'; return; }
    if ( !@_ ) { carp "Useless use of trim with no arguments"; return; }
    @_ = @_ if defined wantarray;

    for (@_) { s/\A\s+//; s/\s+\z// }

    return wantarray ? @_ : "@_";
}