Need help on ksh

Shell Programming and Scripting
1
  1. Script using bash
#!/bin/bash
a=4294967296
(( b=$a / 2 ))
echo "$a"
echo "$b"

*** output ***

4294967296
2147483648
  1. Script using ksh
#!/bin/ksh
a=4294967296
(( b=$a / 2 ))
echo "$a"
echo "$b"

*** output ***

4294967296
0

I am using cygwin to run above scripts. It seems to be working on bash but not on ksh.

Any idea why it is not working on ksh?

2

Your version of ksh on Cygwin is probably pdksh (Public domain ksh.) Check $KSH_VERSION to be certain. pdksh only supports integer arithmetic and uses 32-bit integers for that purpose on Cygwin. Therefore it is limited in the size of the integers which it can handle. As a test, set a to 4000 and see if the result is 2000.

3

Thanks fpmurphy for the clarification.

4

The limit in ksh for integer arithmetic is exactly:
((1024 x 1024 x 1024 x 2) - 1)

expr 2147483647 + 0
2147483647

expr 2147483647 + 1
-2147483648

This limit can be circumvented by using "bc".

echo "2147483647 + 1"|bc
2147483648

Once the numbers are above 2147483647 in ksh, store them in character variables because an integer variable will overflow.