Where is PATH line located in ubuntu 12.04?

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http://www.linuxquestions.org – Where can I modify PATH line in ubuntu 12.04? I typed PATH=$PATH:$HOME then typed export PATH. Home dir was in path when I looked at it with echo $PATH but went away after I relogged in. How can I make it permanent? and where exactly is it in a file in Ubuntu 12.04? (HowTos)