Only use red color for errors if terminal supports ANSI

Sources/Commander/CommandRunner.swift

@@ -38,10 +38,10 @@ extension CommandType {
       error.print()
       exit(1)
     } catch let error as CustomStringConvertible {
-      fputs("\(ANSI.red)\(error.description)\(ANSI.reset)\n", stderr)
+      ANSI.red.print(error.description, to: stderr)
       exit(1)
     } catch {
-      fputs("\(ANSI.red)Unknown error occurred.\(ANSI.reset)\n", stderr)
+      ANSI.red.print("Unknown error occurred.", to: stderr)
       exit(1)
     }
 

Sources/Commander/Error.swift

@@ -13,8 +13,7 @@ protocol ANSIConvertible : Error, CustomStringConvertible {
 extension ANSIConvertible {
   func print() {
     // Check if we are in any term env and the output is a tty.
-    if let termType = getenv("TERM"), String(cString: termType).lowercased() != "dumb" &&
-      isatty(fileno(stdout)) != 0 {
+    if ANSI.isTerminalSupported {
       fputs("\(ansiDescription)\n", stderr)
     } else {
       fputs("\(description)\n", stderr)
@@ -39,4 +38,21 @@ enum ANSI: UInt8, CustomStringConvertible {
   var description: String {
     return "\u{001B}[\(self.rawValue)m"
   }
+
+  static var isTerminalSupported: Bool {
+    if let termType = getenv("TERM"), String(cString: termType).lowercased() != "dumb" &&
+      isatty(fileno(stdout)) != 0 {
+      return true
+    } else {
+      return false
+    }
+  }
+
+  func print(_ string: String, to output: UnsafeMutablePointer<FILE> = stdout) {
+    if ANSI.isTerminalSupported {
+      fputs("\(self)\(string)\(ANSI.reset)\n", output)
+    } else {
+      fputs("\(string)\n", output)
+    }
+  }
 }