Various sign command improvements

- Exit with error if the user is attempting to sign with a key
  whose address is not among those who are expected to sign
  the transaction.

- Add --print-signature-only to output only the generated
  signature.

client/utils/utils.go

@@ -123,7 +123,8 @@ func SignStdTx(txBldr authtxb.TxBuilder, cliCtx context.CLIContext, name string,
 
 	// Check whether the address is a signer
 	if !isTxSigner(sdk.AccAddress(addr), stdTx.GetSigners()) {
-		fmt.Fprintf(os.Stderr, "WARNING: The generated transaction's intended signer does not match the given signer: '%v'\n", name)
+		return signedStdTx, fmt.Errorf(
+			"The generated transaction's intended signer does not match the given signer: %q", name)
 	}
 
 	if !offline && txBldr.AccountNumber == 0 {

x/auth/client/cli/sign.go

@@ -20,6 +20,7 @@ const (
 	flagAppend    = "append"
 	flagPrintSigs = "print-sigs"
 	flagOffline   = "offline"
+	flagSigOnly   = "print-signature-only"
 )
 
 // GetSignCommand returns the sign command
@@ -38,6 +39,7 @@ recommended to set such parameters manually.`,
 	}
 	cmd.Flags().String(client.FlagName, "", "Name of private key with which to sign")
 	cmd.Flags().Bool(flagAppend, true, "Append the signature to the existing ones. If disabled, old signatures would be overwritten")
+	cmd.Flags().Bool(flagSigOnly, false, "Print only the generated signature, then exit.")
 	cmd.Flags().Bool(flagPrintSigs, false, "Print the addresses that must sign the transaction and those who have already signed it, then exit")
 	cmd.Flags().Bool(flagOffline, false, "Offline mode. Do not query local cache.")
 	return cmd
@@ -59,14 +61,24 @@ func makeSignCmd(cdc *amino.Codec, decoder auth.AccountDecoder) func(cmd *cobra.
 		cliCtx := context.NewCLIContext().WithCodec(cdc).WithAccountDecoder(decoder)
 		txBldr := authtxb.NewTxBuilderFromCLI()
 
-		newTx, err := utils.SignStdTx(txBldr, cliCtx, name, stdTx, viper.GetBool(flagAppend), viper.GetBool(flagOffline))
+		// if --print-signature-only is on, then override --append
+		generateSignatureOnly := viper.GetBool(flagSigOnly)
+		append := viper.GetBool(flagAppend) && !generateSignatureOnly
+		newTx, err := utils.SignStdTx(txBldr, cliCtx, name, stdTx, append, viper.GetBool(flagOffline))
 		if err != nil {
 			return err
 		}
+
 		var json []byte
-		if cliCtx.Indent {
+
+		switch {
+		case generateSignatureOnly && cliCtx.Indent:
+			json, err = cdc.MarshalJSONIndent(newTx.Signatures[0], "", "  ")
+		case generateSignatureOnly && !cliCtx.Indent:
+			json, err = cdc.MarshalJSON(newTx.Signatures[0])
+		case !generateSignatureOnly && cliCtx.Indent:
 			json, err = cdc.MarshalJSONIndent(newTx, "", "  ")
-		} else {
+		case !generateSignatureOnly && !cliCtx.Indent:
 			json, err = cdc.MarshalJSON(newTx)
 		}
 		if err != nil {