The only way I could produce the error was if @foo was a shorter array than @bar.

@foo = ( 1 , 3 , 5 , 7 );
@bar = ( 2 , 4 , 6 , 8 , 9);
print STDOUT my @foobar = map { ( $_, shift @foo ) } @bar;
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Unfortunately, I don't know what you want to do if they are not the same size. So I'll guess:

@foo = ( 2 , 4 , 6 , 8 );
@bar = ( 1 , 3 , 5 , 7, 9);
$len = @foo;
print STDOUT my @foobar = (
        (map { ( $_, shift @foo ) } @bar[0 .. $len - 1]),
        @bar[$len .. $#bar]  );
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HTH,
Charles K. Clarkson