Added function getEnvVar() (#196)

* Added function readEnvVar()

* Address linter error

* Addressed review comments

* Update missed variable names

internal/builtinfunctions/functions.go

@@ -35,6 +35,8 @@ func GetFunctions() map[string]schema.CallableFunction {
 	toUpperFunction := getToUpperFunction()
 	splitStringFunction := getSplitStringFunction()
 	loadFileFunction := getReadFileFunction()
+	// OS call functions
+	getEnvVarFunction := getGetEnvVarFunction()
 	// Data transformation functions
 	bindConstantsFunction := getBindConstantsFunction()
 
@@ -57,6 +59,7 @@ func GetFunctions() map[string]schema.CallableFunction {
 		toUpperFunction.ID():                toUpperFunction,
 		splitStringFunction.ID():            splitStringFunction,
 		loadFileFunction.ID():               loadFileFunction,
+		getEnvVarFunction.ID():              getEnvVarFunction,
 		bindConstantsFunction.ID():          bindConstantsFunction,
 	}
 
@@ -529,6 +532,37 @@ func getReadFileFunction() schema.CallableFunction {
 	return funcSchema
 }
 
+func getGetEnvVarFunction() schema.CallableFunction {
+	funcSchema, err := schema.NewCallableFunction(
+		"getEnvVar",
+		[]schema.Type{
+			schema.NewStringSchema(nil, nil, nil), // env var name
+			schema.NewStringSchema(nil, nil, nil), // default value
+		},
+		schema.NewStringSchema(nil, nil, nil),
+		false,
+		schema.NewDisplayValue(
+			schema.PointerTo("getEnvVar"),
+			schema.PointerTo(
+				"Returns the value of a system environment variable.\n"+
+					"Param 1: The name of the environment variable.\n"+
+					"Param 2: The value to return if the environment variable is not present."),
+			nil,
+		),
+		func(envVarName string, defaultValue string) string {
+			envVarValue, envVarPresent := os.LookupEnv(envVarName)
+			if envVarPresent {
+				return envVarValue
+			}
+			return defaultValue
+		},
+	)
+	if err != nil {
+		panic(err)
+	}
+	return funcSchema
+}
+
 // CombinedObjPropertyConstantName is the identifier string key that points to the container of constant or repeated values.
 const CombinedObjPropertyConstantName = "constant"
 

internal/builtinfunctions/functions_test.go

@@ -6,6 +6,7 @@ import (
 	"go.flow.arcalot.io/engine/internal/builtinfunctions"
 	"go.flow.arcalot.io/pluginsdk/schema"
 	"math"
+	"os"
 	"reflect"
 	"regexp"
 	"strings"
@@ -1012,3 +1013,23 @@ func TestBuildSchemaNames(t *testing.T) {
 		})
 	}
 }
+
+func TestGetEnvVarFunction(t *testing.T) {
+	// Set the env variables to get below.
+	knownPresentEnvVarKey := "test_known_present_env_var_key"
+	knownNotPresentEnvVarKey := "test_known_not_present_env_var_key"
+	knownEnvVarValue := "known value"
+	defaultEnvVarValue := "default"
+	assert.NoError(t, os.Setenv(knownPresentEnvVarKey, knownEnvVarValue))
+	assert.NoError(t, os.Unsetenv(knownNotPresentEnvVarKey))
+	assert.MapContainsKey(t, "getEnvVar", builtinfunctions.GetFunctions())
+	getEnvVarFunction := builtinfunctions.GetFunctions()["getEnvVar"]
+	// Test the present env var
+	result, err := getEnvVarFunction.Call([]any{knownPresentEnvVarKey, defaultEnvVarValue})
+	assert.NoError(t, err)
+	assert.Equals(t, result, any(knownEnvVarValue))
+	// Test the missing env var
+	result, err = getEnvVarFunction.Call([]any{knownNotPresentEnvVarKey, defaultEnvVarValue})
+	assert.NoError(t, err)
+	assert.Equals(t, result, any(defaultEnvVarValue))
+}