Shell Programming and Scripting

Hi, I am analisying an existing script. what the below code will do?
if [ ! -a ${REF_file} ]
can some onle tell me what -a will do here. Upto my knowledge it can be used as and.
In this case they gave a comment like-- it will check for the existance of the ref file. I feel -f need to be used to check the existence.

Thanks in advance.

test command has option -a and it same as -e, almost same as -f.
-e file exist
-f file exist and it's regular file
so: test ! -a "$REF_file" will test "if file not exist, then ..."

You can write test or using [ -command, in [ cmd last argument must be ]

if test -f file ; then ...
if [ test -f file ] ; then
are same builtin command

[ is not bracket, it's command

More about if

Thanks for your help...
Here -a is used with if but not with test. As u said can i consider it as -f or -e.