Hi P S Vinay,
It looks like there's a subtle difference between the paths defined in SYBASE.sh and the actual path where isql resides.
Based on the output provided:
bash-3.2$ echo $SYBASE
/cpsybpv1/app/sybase/product/157
bash-3.2$ ls -l /app/sybase/product/157/OCS-15_0/bin/isql
-rwxr-xr-x 1 sybase dba 3794300 Nov 27 2013 /app/sybase/product/157/OCS-15_0/bin/isql
bash-3.2$ /app/sybase/product/157/OCS-15_0/bin/isql -v Sybase CTISQL Utility/15.7/P-EBF22075 SP122/DRV.15.7.0.12/SPARC/Solaris 10/BUILD1570-036/OPT/Wed Nov 27 01:46:40 2013
[snip]
You can see that the environment paths have /cpsybpv1/app/sybase/product/157 prefixed to any of the ASE files. This is inherited from sourcing the SYBASE.sh file. The env output provided does not contain any paths that start with "/app/sybase/product/157"
The real path appears to be /app/sybase/product/157 instead. This would be typical if this was originally installed in the /cpsybpv1/app directory and later these contents were copied over to /app/sybase/product/157 and the SYBASE.(c)sh files weren't updated to reflect the change in pathing.
A quick verification can be done by comparing contents of these 2 paths:
ls /cpsybpv1/app/sybase/product/157
ls /app/sybase/product/157
Cheers
Dan