title: Error installing zmq Node Module
body: <p>When installing the <em>zmq node module</em>, I get the following error. 
  I have the latest stable version of node installed.</p>
  
  <p>I am running a Mac on OS X 10.9.3</p>
  
  <pre><code>npm http GET https://registry.npmjs.org/zmq
  npm http 304 https://registry.npmjs.org/zmq
  npm http GET https://registry.npmjs.org/nan
  npm http GET https://registry.npmjs.org/bindings
  npm http 304 https://registry.npmjs.org/nan
  npm http 304 https://registry.npmjs.org/bindings
  
  &gt; zmq@2.7.0 install /Users/mario/node_modules/zmq
  &gt; node-gyp rebuild
  
  /bin/sh: pkg-config: command not found
  gyp: Call to 'pkg-config libzmq --libs' returned exit status 127. while trying to load binding.gyp
  gyp ERR! configure error 
  gyp ERR! stack Error: `gyp` failed with exit code: 1
  gyp ERR! stack     at ChildProcess.onCpExit (/usr/local/lib/node_modules/npm/node_modules/node-gyp/lib/configure.js:340:16)
  gyp ERR! stack     at ChildProcess.emit (events.js:98:17)
  gyp ERR! stack     at Process.ChildProcess._handle.onexit (child_process.js:809:12)
  gyp ERR! System Darwin 13.2.0
  gyp ERR! command "node" "/usr/local/lib/node_modules/npm/node_modules/node-gyp/bin/node-gyp.js" "rebuild"
  gyp ERR! cwd /Users/mario/node_modules/zmq
  gyp ERR! node -v v0.10.29
  gyp ERR! node-gyp -v v0.13.0
  gyp ERR! not ok 
  npm ERR! zmq@2.7.0 install: `node-gyp rebuild`
  npm ERR! Exit status 1
  npm ERR! 
  npm ERR! Failed at the zmq@2.7.0 install script.
  npm ERR! This is most likely a problem with the zmq package,
  npm ERR! not with npm itself.
  npm ERR! Tell the author that this fails on your system:
  npm ERR!     node-gyp rebuild
  npm ERR! You can get their info via:
  npm ERR!     npm owner ls zmq
  npm ERR! There is likely additional logging output above.
  
  npm ERR! System Darwin 13.2.0
  npm ERR! command "/usr/local/bin/node" "/usr/local/bin/npm" "install" "zmq"
  npm ERR! cwd /Users/mario/messaging
  npm ERR! node -v v0.10.29
  npm ERR! npm -v 1.4.9
  npm ERR! code ELIFECYCLE
  npm ERR! 
  npm ERR! Additional logging details can be found in:
  npm ERR!     /Users/mario/messaging/npm-debug.log
  npm ERR! not ok code 0
  </code></pre>
  
  <p>Why do I get this error and what should I do to fix it?</p>