^ and $ can be combined to match an entire line. For example, the following regex will match a line that starts with the # character and ends with the . character, with any number of other characters in-between:

$ grep '^#.*\.$' /etc/fstab
# /etc/fstab: static file system information.

In the above example, we surrounded our regular expression with single quotes to prevent $ from being interpreted by the shell. Without the single quotes, the $ will disappear from our regex before grep even has a chance to take a look at it.