check if geth command exists and warn user if not

lib/cmds/blockchain/blockchain.js

@@ -50,12 +50,26 @@ Blockchain.prototype.run = function() {
   console.log(("Embark Blockchain Using: " + this.client.name.underline).magenta);
   console.log("===============================================================================".magenta);
   console.log("===============================================================================".magenta);
+  if (!this.isClientInstalled()) {
+    console.log(("could not find " + this.config.geth_bin + " command; is " + this.client.name + " installed or in the PATH?").green);
+    return;
+  }
   var address = this.initChainAndGetAddress();
   this.client.mainCommand(address, function(cmd) {
     self.runCommand(cmd, {async: true});
   });
 };
 
+Blockchain.prototype.isClientInstalled = function() {
+  let versionCmd = this.client.determineVersion();
+  let result = this.runCommand(versionCmd);
+
+  if (result.output === undefined || result.output.indexOf("not found") >= 0) {
+    return false;
+  }
+  return true;
+};
+
 Blockchain.prototype.initChainAndGetAddress = function() {
   var address = null, result;
 
@@ -94,4 +108,3 @@ var BlockchainClient = function(blockchainConfig, client, env) {
 };
 
 module.exports = BlockchainClient;
-

lib/cmds/blockchain/geth_commands.js

@@ -34,6 +34,10 @@ class GethCommands {
     return cmd;
   }
 
+  determineVersion() {
+    return this.geth_bin + " version";
+  }
+
   determineNetworkType(config) {
     let cmd = "";
     if (config.networkType === 'testnet') {
@@ -203,4 +207,3 @@ class GethCommands {
 }
 
 module.exports = GethCommands;
-