Temporarily changing default gid

I was not satisfied with just chgrp -R files that were created with SVN so decided to do some research on how Linux determines which gid to assign to a file when created.

I was hoping that it was as simple as just changing an environment variable but that was not the case. However, I came across this tlpd.org page:

http://tldp.org/LDP/intro-linux/html/sect_03_04.html

It brought to my attention the newgrp and id commands. I wrote up a quick  wiki article about this.