Bitwise negation Post: 302117669

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Top Forums Shell Programming and Scripting Bitwise negation Post 302117669 by Perderabo on Wednesday 16th of May 2007 12:19:11 AM

05-16-2007

Administrator Emeritus

If the course says that ((~ 2#1001)) evaluates to 2#110, I wonder what shell they were using. With ksh I get:
$ typeset -i2 b
$ echo $((2#1001)) $((b=~2#1001)) $b
9 -10 -2#1010

With bash, there is no -i2 and I don't see an easy way to get binary output. I could code my own routine, but then the behavior would be whatever I decided. (But I get the "9 -10" part with bash.) Since ksh alone has a way to output binary, I did a few experiments with it. A negative number has many leading 1's while a non-negative has many leading zeros. ksh uses enough positions to output the the leftmost bit transistion. If you exceed the shell's integer size, you get undefined results, but clamping at positive or negative "infinity" (max/min integer) is common with both ksh and bash. The shells I checked have either 32 or 64 bit integers.

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suspend

suspend(1)                                                         User Commands                                                        suspend(1)

NAME

       suspend - shell built-in function to halt the current shell

SYNOPSIS

   sh
       suspend

   csh
       suspend

   ksh
       suspend

DESCRIPTION

   sh
       Stops the execution of the current shell (but not if it is the login shell).

   csh
       Stop the shell in its tracks, much as if it had been sent a stop signal with ^Z. This is most often used to stop shells started by su.

   ksh
       Stops the execution of the current shell (but not if it is the login shell).

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE         |      ATTRIBUTE VALUE        |
       +-----------------------------+-----------------------------+
       |Availability                 |SUNWcsu                      |
       +-----------------------------+-----------------------------+

SEE ALSO

       csh(1), kill(1), ksh(1), sh(1), su(1M), attributes(5)

SunOS 5.10                                                          15 Apr 1994                                                         suspend(1)