re: tcsh thinks the / following the colon in

echo "export PATH=$PATH:/p/course/cs400/public/scripts/" >> ~/.bashrc
                  ~~~~~~^

is a modifier, and it complains because / isn't a valid modifier (a csh modifier is usually a single letter). Apparently this is not what we mean by "$PATH:/" so, a few ways to make this line work in tcsh (also work in bash/zsh):

1. Protect PATH from the colon with braces:

   echo "export PATH=${PATH}:/p/course/cs400/public/scripts/" >> ~/.bashrc

2. Quote $PATH separately from the colon:

   echo "export PATH=$PATH":/p/course/cs400/public/scripts/ >> ~/.bashrc

Though in all honesty, we should just disable variable interpolation altogether with single quotes...

echo 'export PATH="$PATH":/p/course/cs400/public/scripts/' >> ~/.bashrc

P.S. tcsh is probably not going to look at ~/.bashrc. So unless you change your login shell to bash (chances are you want this), you probably want to consider changing ~/.bashrc in that command to something like ~/.cshrc or ~/.tcshrc (review the FILES section of man tcsh).

P.P.S. Also, export doesn't exist in csh/tcsh. You want setenv, e.g. setenv PATH ${PATH}:/p/course/cs400/public/scripts/. csh is quite different from Bash and other Bourne-like shells! (But then again you can switch to Bash since that's what they teach here...)