You can use sed to perform text substitution in files. Suppose you want to change the string "old" to "new" in all the header files in a directory. You can accomplish this with the following command in a bash shell.
for x in $(ls *.h); do sed 's/old/new/g' $x >t; mv t $x; done
Use the following command to add your passphrase to your keychain.
ssh-add -K