#358 Handle the case where input iceberg files are empty

If input files have no icebergs, then use one of the
empty input files as the output file. This will indicate
that there are no icebergs, and the iceberg model can
accept a restart file with no icebergs (per Alex Huth).

Author: ceblanton

src/iceberg-comb/iceberg_comb.sh.in

@@ -330,17 +330,39 @@ do
     has_icebergs $f && combine_files="$combine_files $f"
 done
 
-# Run ncrcat on the files
-ncrcat_cmd="$ncrcat $combine_files $out_file"
-if [ $verbose -gt 0 ]
+# Normally, run ncrcat on the input files. However,
+# if all input files have no icebergs, then use one of the input files
+# as the output file, print a message, and exit normally.
+# This unambigously indicates that there are no icebergs,
+# and the iceberg model can read an iceberg restart with no icebergs.
+if [ -n "$combine_files" ]
 then
-    echoerr "debug1: Running '$ncrcat_cmd'"
-fi
-eval $ncrcat_cmd
-if [ $? -ne 0 ]
-then
-    echoerr "$script_name: Error during executing '$ncrcat_cmd'"
-    exit $EXIT_FAILURE
+    # Run ncrcat on the files
+    ncrcat_cmd="$ncrcat $combine_files $out_file"
+    if [ $verbose -gt 0 ]
+    then
+        echoerr "debug1: Running '$ncrcat_cmd'"
+    fi
+    eval $ncrcat_cmd
+    if [ $? -ne 0 ]
+    then
+        echoerr "$script_name: Error during executing '$ncrcat_cmd'"
+        exit $EXIT_FAILURE
+    fi
+else
+    # Copy first empty iceberg file to the output file
+    echoerr "debug1: Input files contain no icebergs; this is fine"
+    copy_cmd="cp ${in_files%% *} $out_file"
+    if [ $verbose -gt 0 ]
+    then
+        echoerr "debug1: Running '$copy_cmd'"
+    fi
+    $copy_cmd
+    if [ $? -ne 0 ]
+    then
+        echoerr "$script_name: Error during executing '$copy_cmd'"
+        exit $EXIT_FAILURE
+    fi
 fi
 
 ncatted_cmd="$ncatted -a NumFilesInSet,global,d,, $out_file"