i have textfiles that contain a series of lines that look like this:

string0 .................................................... column3a column4a
string1**384y0439 ..................................... column3b column4b
string2**23903990 ..................................... column3c column4c
string3 .................................................. column3d column4d
string4**67823678 ..................................... column3e column4e

can you help me write a C-shell script that will list all the unique strings before the ** ?
if a string is not followed by ** (eg. string0 and string3), the string should be in the list, whether or not it is unique.
I think I need to first filter out the lines without .................................. (which are always at the beginning and end part of the textfile).

can anyone help me with this please?
thanks a lot!