Anchors in Regular Expressions

Question

^ specifies that the match must start at the beginning of a line or string.

What does string mean?

Does it mean /^(apple)/ will match this applesauce is delicious, as apple is beginning of the string applesauce.

Does ^ always have to be in the beginning of the search in regex engine?

Why isn't his matched /apple ^(his)/?

apple 
his

since his is in the beginning of the string?

Please escape the meaning of ^ in character sets.

Answer 1

No, ^ or \A is not always necessary for a regular expression. Sometimes we would include them in our expressions, if required, especially for validating strings.

In your example, this applesauce is delicious is the string, and ^(apple) will not match our string here, because our string does not start with apple, starts with this:

Demo 1

If we remove the start anchor, our expression would look like:

(apple)

which has a capturing group (), then that would find and capture apple in any part of our string.

Demo 2

If we add a word boundary to our expression, for instance:

(\bapple\b)

then, we would be only finding apple as a separate word, not as a part of a sub-string, if you will, thus we would not capture applesauce.

Demo 3

RegEx Circuit

jex.im visualizes regular expressions:

Difference between line and string

String refers to the entire input to our expression, which may be only one line or may consist of several lines (such as a paragraph). For instance, this is considered a string, which has multiple lines:

this applesauce is delicious this applesauce is delicious
apple is delicious apple is delicious

apple is delicious

apple is delicious

apple is delicious

Demo 4

Great Question

In the last question, apple ^(his) will not match:

apple 
his

because there is a new line between apple and his, yet an space ( ) or \s is not sufficient, however

apple\s*^(his)

will match that, since \s* passes both space and new lines as well, even though ^ may not be necessary there.

Demo 5