In a 32-bit int, 

$core_dumped = ($? >> 15) & 1;

00000000 00000000 CSSSSSSS EEEEEEEE

   >> 15

00000000 00000000 00000000 0000000C

   & 1

00000000 00000000 00000000 00000001 = 1
00000000 00000000 00000000 0000000C

[download]

Ok, everything to the left of "C" should always be zero, so the & 1 doesn't do anything. Me bad. The signal one is a better example: 

$signal = ($? >> 8) & 127;

00000000 00000000 CSSSSSSS EEEEEEEE

   >> 8

00000000 00000000 00000000 CSSSSSSS

   & 127

00000000 00000000 00000000 01111111 = 127
00000000 00000000 00000000 0SSSSSSS

[download]

The shift repositioned the bits of interest and removed the lower-precision bits we didn't want.

The "and" removed the higher-precision bits we didn't want.

You could do the operations in the opposite order: 

$signal = ($? & 0x7F00) >> 8;

00000000 00000000 CSSSSSSS EEEEEEEE

   & 0x00007F00

00000000 00000000 01111111 00000000 = 0x00007F00
00000000 00000000 0SSSSSSS 00000000

   >> 8

00000000 00000000 00000000 0SSSSSSS

[download]

The "and" removed all the bits we didn't want.

The shift repositioned the bits of interest.

You should be start by understanding how machines store integers.

In reply to Re^3: Shift Operators And Bitwise Operators by ikegami
in thread Shift Operators And Bitwise Operators by biohisham

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