A coworker of mine wants to add some environment variables to env file. Please advise how to do it. He couldn't use: more or vi on the file. Thanks.

What env file? Do you mean the actual environment? You can't use vi on the environment, you have to directly set the variables. In sh/ksh/bash, you can set the env variables like this:
In csh/tcsh, you do it like this:
If you want to have the variables set automatically when you login, set the variables in the appropriate files. You can get the filenames from the man pages of the appropriate shell.

/etc/environment and /etc/profile will set the global variables. Do not forget that the local .profile will make modifications. This answer is from an AIX prospective but I believe the files are the same across all platforms.

blowtorch, johnf:

Thanks so much. Very clear description. I will tell my coworker.