How to detect if a specific file exists in Vimscript?

Some of the comments express concerns about filereadable and using glob instead. This addresses the issue of having a file that does exist, but permissions prevent it from being read. If you want to detect such cases, the following will work:

:if !empty(glob("path/to/file"))
:   echo "File exists."
:endif

With a bit of searching in vim man I've found this, which looks much better that the original:

:function! SomeCheck()
:   if filereadable("SpecificFile")
:       echo "SpecificFile exists"
:   endif
:endfunction