Mastering Bash

Bitwise NOT (~)

The bitwise NOT is a unary operator, and this means it is used with just one operator, flipping the bit used to represent the integer in binary notation:

zarrelli:~$ x=50 ; echo $((~x))-51  

Have a look at the following table:

128	64	32	16	8	4	2	1
50	0	0	1	1	0	0	1	0
~	1	1	0	0	1	1	0	1
-128	64	8	4	1

 

We have to keep in mind that the most significant bit on the left for a signed integer (and this is a signed integer, even though we do not write +50 because Bash represents integer with a sign long at 64-bit) holds the sign value. So, flipping the first significant bit actually inverted the value. As the rule of thumb, the bitwise NOT leads to the same ...