Search and replace with sed when dots and underscores are present

Question

How do I replace foo. with foo_ with sed simply running

sed \'s/foo./foo_/g\' file.php

doesn\'t work. Thanks!

Answer 1

Escape the .:

sed 's/foo\./foo_/g' file.php

Example:

~$ cat test.txt 
foo.bar
~$ sed 's/foo\./foo_/g' test.txt 
foo_bar