There are two commands for searching through the current source file for a regular expression.
The command forward-search regexp checks each line, starting with the one following the last line listed, for a match for regexp. It lists the line that is found. You can use the synonym search regexp or abbreviate the command name as fo.
The command reverse-search regexp checks each line, starting with the one before the last line listed and going backward, for a match for regexp. It lists the line that is found. You can abbreviate this command as rev.