How can I open a file read-only from command line with emacs/vi/vim

vim -R filename

For emacs:

emacs FILE --eval '(setq buffer-read-only t)'

There's no startup option to force read only.

Edit:
If you put this small function in your shell startup script (.bashrc for example) you can open a file read-only by typing ev file_to_view

ev() {
  emacs "$1" --eval '(setq buffer-read-only t)'
}

view filename

Basically vim in read-only mode; simples!

As hinted by comment, in case view is linked to plain vi, here are bash commands to first inspect situation and then fix it:

# non-destructive inspection
which vim
which view
ls -l $(which view)

# overwrite current view with symlink to vim, requires root
ln -sfv $(which vim) $(which view)