How to restore a removed /bin/sh file?
Run this command to copy /bin/sh from the BaseSystem.dmg on the Recovery HD:

diskutil mount Recovery\ HD &amp;&amp;
    hdiutil mount /Volumes/Recovery\ HD/com.apple.recovery.boot/BaseSystem.dmg &amp;&amp;
    sudo cp -p /Volumes/OS\ X\ Base\ System/bin/sh /bin/sh


Also see How can I get back a system file after deleting it from my Mac?