KSH expr command integer overflow

Last night we have recived false alerts about a filesystem space issue. It turns out there is a bug in the script related to integer overflow in the "expr" command. I found this overflow error can be see on our HP-UX system, but not on Solaris or Linux machines. Here are the testing results:

----------- test script: test.ksh begins next line -----------------
#!/bin/ksh
## Bad##
FS=2840644712
FS=`expr $FS / 1024` ;
echo $FS
## Good##
FS=2840644712
FS=`echo $FS/1024 bc `
echo $FS
----------- test script ends last line -----------------


HP-UX
~~~~~~~~

$ uname -a
HP-UX dhpnbe5 B.11.23 U ia64 3928363565 unlimited-user license
$ ./test.ksh
-1420236
2774067


Linux
~~~~~~

$ uname -a
Linux wrpe2e06.edc.mycompany.net 2.6.9-55.0.9.ELlargesmp #1 SMP Tue Sep 25 02:25:48 EDT 2007 x86_64 x86_64 x86_64 GNU/Linux
oracle@wrpe2e06.edc.mycompany.net(!) ph1etem3 /tmp
$ ./test.ksh
2774067
2774067


Solaris
~~~~~~~

$ uname -a
SunOS wspebp06 5.10 Generic_127111-11 sun4u sparc SUNW,Sun-Fire
$ ./test.ksh
2774067
2774067