Skipping files and continue

[Meredith Croke]

 Hi All,

I'm new to GrADS and am trying to write a script that opens one file at
a time, performs a funtion, writes the data to a .dat file, then closes
and opens the next ctl file.  I have several hundred files that I am
opening.  The problem I am running into is this; all the CTL files
exist, however there are a few data files that do not exist.  When it
reaches these files I get a segmentation fault.  Is there anyway I can
write a statement that says if the file does not exist to print some
value (either 999 or NA), add 3 to the hour and continue to the next
file?

Thank you very much for your help!

Meredith