What does $(( x^y )) actually do ?

[pete of ebor]

I was just playing about with some simple bash scripts trying to get to grips with arithmetic expansions. I'm aware that to do exponentiation, the operator is a double-asterisk - e.g. $(( 2**4 )) = 16. I tried $(( 2^4 )) to see what would happen. I expected some sort of error, but I got the answer 6. I then wrote a short loop script to do this for x^y where x & Y both ranged from 1-100, and I got a valid answer every time - but I can't work out what it is actually doing. I've searched but to no avail. I'm just curious..

[xenopeek]

The manual says ^ is a bitwise exclusive OR operation: https://www.gnu.org/software/bash/manua ... metic.html

Bitwise exclusive OR means to compare each bit of the operands and set the corresponding bit in the result to 1 if the bits differ, or to 0 if they are equal.

Code: Select all

  0010 (2 decimal written as binary)
  0100 (4 decimal written as binary)
^ ----
  0110 = 6 in decimal

[Moonstone Man]

I tried $(( 2^4 )) to see what would happen. I expected some sort of error, but I got the answer 6.

Bitwise XOR.

https://www.gnu.org/software/bash/manua ... metic.html

[1000]

Code: Select all

Input   Input   |    Output
A 	B 	|    A OR B
_________________________
0 	0 	|    0
0 	1 	|    1
1 	0 	|    1
1 	1 	|    1 

Table - how " OR " working from: https://en.wikipedia.org/wiki/OR_gate

[xenopeek]

Code: Select all

Input   Input   |    Output
A 	B 	|    A OR B
_________________________
0 	0 	|    0
0 	1 	|    1
1 	0 	|    1
1 	1 	|    1 

Table - how " OR " working from: https://en.wikipedia.org/wiki/OR_gate

Irrelevant, this is about XOR.

[1000]

True. My fault
" bitwise exclusive OR " = XOR

[pete of ebor]

Thanks for the replies.. I'm obviously not very good at searching !
As they say, if all else fails, RTFM !