s/[pattern_to_find]/[pattern_to_replace_with]/

Thus, for example, the line:

     s/eric/selena/

would change the line

     eric is my name

to

     selena is my name

The substitution function is modified most commonly with the /i and the /g arguments. The /i argument specifies that matching should be done with case insensitivity and the /g specifies that the match should occur globally for the entire string of text rather than just for the first occurrence.

Thus, the line

     s/eric/selena/gi

would change the line:

     I am Eric, eric I am

to

     I am selena, selena I am

without the /i, you would get

     I am Eric, selena I am

and without /g but with the /i, you would get

     I am selena, eric I am

There are many, many different kinds of matching operators, anchors, and string modifiers. If you want a more detailed explanation I recommend that you find a good reference source on Regular Expressions. Otherwise, the above discussion should explain how operators and anchors are commonly used in CGI applications.