Under Solaris UNIX I have a bunch of files in a directory with a
common prefix  that I wish to move into a subdirectory.  I don't want
to have to enter "mv file_one subdir/file_one" for each of the files
as this would be time consuming. What I'd like to do is something on
the command line that would move all the files I need to move into the
subdirectory in one line.  All the files have a similar prefix, so I
was hoping that would allow me to somehow do this easily without
moving files in the same directory that don't have this prefix. 
Thanks for your help.

Using your format, the following should work:

mv file*.* subdir

If you need to write over some existing files, do a force:

mv -f file*.* subdir

I think this should work:

mv file_* subdir/

where file_ is the prefix.