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Philip Kirkbride

00:01

Does anyone know the name for the pattern where a number represents true or false for multiple columns.

e.g. what is used for chmod 777

Where 7 is 1+2+4

I want to search something related to this but not related to chmod at all.

5 hours later…

Faheem Mitha

05:22

@derobert Based on my small and unscientific test. your change to the hashdeep answer is the correct one.

1 hour later…

Kusalananda

06:36

@PhilipKirkbride "mask"? With chmod, the number is called the "mode" operand of the command which will change the "file mode bits" of the affected files/directories/etc.

With open() you specify "flags" that are OR-ed together in a similar manner.

In both cases, you effectively create a "bit mask".

Mask (computing)

In computer science, a mask is data that is used for bitwise operations, particularly in a bit field. Using a mask, multiple bits in a byte, nibble, word etc .. can be set either on, off or inverted from on to off (or vice versa) in a single bitwise operation. == Common bitmask functions == === Masking bits to 1 === To turn certain bits on, the bitwise OR operation can be used, following the principle that Y OR 1 = 1 and Y OR 0 = Y. Therefore, to make sure a bit is on, OR can be used with a 1. To leave a bit unchanged, OR is used with a 0. Example: Masking on the higher nibble (bits 4, ...

3 hours later…

Faheem Mitha

09:15

@Kusalananda No need to apologise for being friendly.

There's too little of that in this world.

Kusalananda

@FaheemMitha True, but as an introvert I can relate to being dragged into a social situation that I just want to observe, not be part of. :-)

Faheem Mitha

@Kusalananda If you said that to me, I would probably just have replied - hi there.

And for the record, you can welcome me anytime. :-)

7 hours later…