feat: system/exec() function call (#1067)

Co-authored-by: Matthew Forrester <matthew.forrester@speechmarks.com>

internal/pkg/bifs/system.go

@@ -44,3 +44,61 @@ func BIF_system(input1 *mlrval.Mlrval) *mlrval.Mlrval {
 
 	return mlrval.FromString(outputString)
 }
+
+func BIF_exec(mlrvals []*mlrval.Mlrval) *mlrval.Mlrval {
+
+	if len(mlrvals) == 0 {
+		return mlrval.ERROR
+	}
+
+	cmd := exec.Command(mlrvals[0].AcquireStringValue())
+	combinedOutput := false
+
+	args := []string { mlrvals[0].AcquireStringValue() }
+	if len(mlrvals) > 1 {
+		for _, val := range mlrvals[1].GetArray()[0:] {
+			args = append(args, val.AcquireStringValue())
+		}
+	}
+	cmd.Args = args
+
+	if len(mlrvals) > 2 {
+
+		for pe := mlrvals[2].AcquireMapValue().Head; pe != nil; pe = pe.Next {
+			if pe.Key == "env" {
+				env := []string {}
+				for _, val := range pe.Value.GetArray()[0:] {
+					env = append(env, val.AcquireStringValue())
+				}
+				cmd.Env = env
+			}
+			if pe.Key == "dir" {
+				cmd.Dir = pe.Value.AcquireStringValue()
+			}
+			if pe.Key == "combined_output" {
+				combinedOutput = pe.Value.AcquireBoolValue()
+			}
+
+			if pe.Key == "stdin_string" {
+				cmd.Stdin = strings.NewReader(pe.Value.AcquireStringValue())
+			}
+		}
+
+	}
+
+	outputBytes := []byte(nil)
+	err := error(nil)
+
+	if combinedOutput {
+		outputBytes, err = cmd.CombinedOutput()
+	} else {
+		outputBytes, err = cmd.Output()
+	}
+
+	if err != nil {
+		return mlrval.ERROR
+	}
+
+	outputString := strings.TrimRight(string(outputBytes), "\n")
+	return mlrval.FromString(outputString)
+}

internal/pkg/dsl/cst/builtin_function_manager.go

@@ -1928,6 +1928,24 @@ either case it should return a boolean.`,
 			unaryFunc: bifs.BIF_system,
 		},
 
+		{
+			name:      "exec",
+			class:     FUNC_CLASS_SYSTEM,
+			help:      `'$output = exec(
+	"command",
+	["arg1", "arg2"],
+	{"env": ["ENV_VAR=ENV_VALUE"],
+	"dir": "/tmp/run_command_here",
+	"stdin_string": "this is input fed to program",
+	"combined_output": true
+)'
+Run a command via executable, path, args and environment, yielding its stdout minus final carriage return.`,
+			examples: []string{
+				`exec("echo", ["Hello", "$YOUR_NAME"], {"env": "YOUR_NAME=World"}) outputs "Hello World"`,
+			},
+			variadicFunc: bifs.BIF_exec,
+		},
+
 		{
 			name:     "version",
 			class:    FUNC_CLASS_SYSTEM,