[ferret_users] Check file exist before saving it

["Yu, Hao-Cheng" <danish.url@xxxxxxxxx>]

Dear ferret users,

I would like to check file existence before saving it.

For example,

use test1.nc

! add check existence code here

save/i=1:10/j=1:10/l=2/file=test2.nc var1,var2

Adding /clob will overwrite file, but if no /clob and file exist, ferret will stop and shows error.

So just curious about any ferret code could check this.

Sincerely, dan