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in this simple example. i am not able to figure what is the bitwise funtion doing:

my [at] subArray = grep { $_ & 1 } [at] array;

what is the significance of 1 here?

is this equivalent? { 1 & $_ }

does the EXPR inside grep's curly braces have to produce the grepped text or just a true false value? i thought like in regular shell it produces whatever it grepped.


thx.

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On 14/08/2011 23:19, Rajeev Prasad wrote:
>
> in this simple example. i am not able to figure what is the bitwise
> funtion doing:
>
> my [at] subArray = grep { $_& 1 } [at] array;

The & operator requires the types of its operands to be identical -
either string or numeric. In either case the values are ANDed together
to produce a value of the same type.

> what is the significance of 1 here?

It is a numeric value with just bit zero set. It is ANDed with the value
in $_ so that if $_ holds an odd or even number the result will be 1 or 0.

> is this equivalent? { 1& $_ }

Yes.

> does the EXPR inside grep's curly braces have to produce the grepped
> text or just a true false value? i thought like in regular shell it
> produces whatever it grepped.

The result of the Perl grep operator is a list where the expression is
true. In this case, [at] subArray becomes a copy of the odd elements of
[at] array (those that, when ANDed with 1 are non-zero).


HTH,

Rob

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