what are the things need to take care when porting shell script from solaris to RHEL 6.0

Not much, particularly if your existing shell program is KornShell (might need to install KornShell on RHEL though). Even at that, KornShell and BASH are pretty much compatible (BASH is, after all, a port of Bourne and Korn).

Copy it over, see if it runs all right (then fix whatever syntax fails). The only things that might be troublesome would be executing Solaris-specific utilities in your shell program (I can't think of what those are right now, sorry, it's been a while). Too, any mounts or unmounts of disks and devices will need editing.

A well-written shell program written in KornShell or Bourne or BASH on Solaris should run just fine on a Linux box (with the proviso about specific utilities and mounting file systems and devices). It shouldn't be too much of a hassle to port.

Hope this helps some.

[EDIT]
Forgot C-Shell. With that, well, might be an enormous pain in the hiney. Might "just work," might not. Best way to find out is the acid test: run it and see.
[/EDIT]

redhat dose backport to old versions BUT!!!
RHEL 6.0
6.0 is 6 minor versions and 3+ years out of date

if you HAVE!!!! to run 6.0 and ONLY!!! 6.0
you must be paying redhat a ton of cash every year

you might want to use that very very expensive support to keep you locked as 6.0 and not the current 6.6

if using korn then not much of a change

as above

run tests there might be a few things here and there