Final answer:
The expression '\.$' in regex matches a period at the end of a line. It combines the escaped dot to match a literal period and the dollar sign as an anchor to signify the end of a line.
Step-by-step explanation:
The expression '\.$' is commonly used in regular expressions. A regular expression (regex) is a pattern that describes a set of strings. The backslash (\) is an escape character in regex, and it is used to denote that what follows is a special character or to allow special characters to be used as literals. The dot (.) in a regex typically matches any single character except for newline characters.
However, when the dot is preceded by a backslash (\.), it becomes a literal dot. The dollar sign ($) is an anchor character that matches the end of a line. So, when they are combined to form '\.$', the regex pattern matches a period at the end of a line. This is useful when you need to find and possibly replace periods that signify the end of sentences or lines in a text processing context.
So, when you put it all together, '\.$' will match a string only if it ends with a period. Here are some examples:
"example.": Matches because it ends with a period.
"no match": Does not match because it does not end with a period.
"another example..": Does not match because it ends with two periods.
Keep in mind that the use of regular expressions may vary depending on the programming language or tool you are using.