my @foo = qw/a b c d e f g/;
for my $x (@foo) {
    push @foo, 'd' if $x eq 'd';
    print $x;
}

##</code><code>##

push @foo, map {$_ eq 'd' ? 'd' : ()} @foo;
print for @foo;

##</code><code>##

for (@foo) {
  print;
  shift(@foo) if $_ eq 'c';
}
print "\n@foo\n";