How to abort python fabric run command?

run("if [ -d data.bak ];then mv data.bak data;fi;")
sudo('....')
sudo('')

I am using fabric deploy for my web project. I want to fin开发者_JAVA百科d a way that will stop the rest of the execution of the command, if it doesn't find the data.bak directory. Any way to achieve this in fabric?

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There is a contribute api in fabric.contrib.files import.