From 8a0073aeb9cfd2aca4439f3a7a9f4010d3349417 Mon Sep 17 00:00:00 2001
From: Shahram Najm <masn@ecmwf.int>
Date: Thu, 2 Feb 2023 10:38:18 +0000
Subject: [PATCH] ECC-1520: grib_filter/bufr_filter: Provide way of reading
 environment variables

---
 src/grib_expression_class_functor.cc | 37 ++++++++++++++++++++--------
 tests/grib_filter.sh                 | 23 +++++++++++++++++
 2 files changed, 50 insertions(+), 10 deletions(-)

diff --git a/src/grib_expression_class_functor.cc b/src/grib_expression_class_functor.cc
index 8a36b68c9..91f4cdcaf 100644
--- a/src/grib_expression_class_functor.cc
+++ b/src/grib_expression_class_functor.cc
@@ -88,9 +88,7 @@ static int evaluate_long(grib_expression* g, grib_handle* h, long* lres)
 {
     grib_expression_functor* e = (grib_expression_functor*)g;
 
-    /*
-    TODO: needs OO code here
-     */
+    // TODO: needs OO code here
     if (strcmp(e->name, "lookup") == 0) {
         return GRIB_SUCCESS;
     }
@@ -113,16 +111,15 @@ static int evaluate_long(grib_expression* g, grib_handle* h, long* lres)
             }
             err = grib_get_long_internal(h, p, &val);
             if (err) return err;
-            /* Note: This does not cope with keys like typeOfSecondFixedSurface
-             * which are codetable entries with values like 255: this value is
-             * not classed as 'missing'!
-             * (See ECC-594)
-             */
+            // Note: This does not cope with keys like typeOfSecondFixedSurface
+            // which are codetable entries with values like 255: this value is
+            // not classed as 'missing'!
+            // (See ECC-594)
             *lres = (val == GRIB_MISSING_LONG);
             return GRIB_SUCCESS;
         }
         else {
-            /* No arguments means return the actual integer missing value */
+            // No arguments means return the actual integer missing value
             *lres = GRIB_MISSING_LONG;
         }
         return GRIB_SUCCESS;
@@ -140,6 +137,26 @@ static int evaluate_long(grib_expression* g, grib_handle* h, long* lres)
         return GRIB_SUCCESS;
     }
 
+    if (strcmp(e->name, "environment_variable") == 0) {
+        // ECC-1520: This implementation has some limitations:
+        // 1. Cannot distinguish between environment variable NOT SET
+        //    and SET but equal to 0
+        // 2. Cannot deal with string values
+        const char* p = grib_arguments_get_name(h, e->args, 0);
+        if (p) {
+            char* env = getenv(p);
+            if (env) {
+                long lval = 0;
+                if (string_to_long(env, &lval) == GRIB_SUCCESS) {
+                    *lres = lval;
+                    return GRIB_SUCCESS;
+                }
+            }
+        }
+        *lres = 0;
+        return GRIB_SUCCESS;
+    }
+
     if (strcmp(e->name, "changed") == 0) {
         *lres = 1;
         return GRIB_SUCCESS;
@@ -157,7 +174,7 @@ static void print(grib_context* c, grib_expression* g, grib_handle* f)
 {
     grib_expression_functor* e = (grib_expression_functor*)g;
     printf("%s(", e->name);
-    /*grib_expression_print(c,e->args,f);*/
+    // grib_expression_print(c,e->args,f);
     printf(")");
 }
 
diff --git a/tests/grib_filter.sh b/tests/grib_filter.sh
index e85d5727b..39636c60c 100755
--- a/tests/grib_filter.sh
+++ b/tests/grib_filter.sh
@@ -242,6 +242,29 @@ EOF
 diff $tempRef $tempOut
 
 
+echo "Test environment variables"
+# -----------------------------------------
+input="${samp_dir}/GRIB2.tmpl"
+cat >$tempFilt <<EOF
+  transient cds = environment_variable(CDS);
+  if (cds == 0) {
+    print "Either CDS is undefined or defined but equal to 0";
+  } else {
+    print "CDS is defined and equal to [cds]";
+  }
+EOF
+# No env var or zero
+${tools_dir}/grib_filter $tempFilt $input > $tempOut
+grep -q "undefined" $tempOut
+CDS=0 ${tools_dir}/grib_filter $tempFilt $input > $tempOut
+grep -q "defined but equal to 0" $tempOut
+# Set to a non-zero integer
+CDS=1 ${tools_dir}/grib_filter $tempFilt $input > $tempOut
+grep -q "defined and equal to 1" $tempOut
+CDS=-42 ${tools_dir}/grib_filter $tempFilt $input > $tempOut
+grep -q "defined and equal to -42" $tempOut
+
+
 echo "Test IEEE float overflow"
 # -----------------------------------------
 input="${samp_dir}/GRIB2.tmpl"