To replace content of file in unix / linux, use sed.
Basic use, first try outputting to terminal:
sed s/blue/black/ file.txt
you can then do either
sed s/blue/black/ file.txt > replaced.txt
sed -i s/blue/black/ file.txt
Last command makes changes directly to file.
If you need to use non-alphabetic-characters, use \ – char in front of them. For example:
sed s/file\.txt/nonfile\.txt/ filetoreplace
More, much more : http://www.grymoire.com/Unix/Sed.html#uh-8