In this lesson, we'll learn about special characters that are used to clarify positions of characters in strings and substrings.
Let's look at the following example:
/java
/
java
Here, the word java
matches the string java
. This is a simple condition. It's important to remember that regular expressions don't look for matches in strings, but in substrings. If you search in a string that contains characters besides the ones you're looking for, the check may show that the strings match, even though that isn't what you want:
/java
/
asdfjava
asdf
There are special characters to control character search in a string.
If you put ^
in the search string before the characters you're looking for, only the characters that are at the beginning of the string will match:
/^java
/
java
ruby clojurescript javascript
If we remove ^
, we'll have two matches, including one in the last substring:
/java
/
java
ruby clojurescript java
script
This character is $
. Here is an example without using this character, with two matches:
/script
/
java ruby clojurescript
javascript
If we use $, then there's only one match, at the end of the string
/script$
/
java ruby clojurescript javascript
Suppose we only need to find instances of a
, that are at the end of a word. To do this, we type a\b
in the string pattern:
/a\b
/
java
ruby clojurescript javascript
If we type \B
, instead, we can invert the search and find all instances of a
, that are not at the end of a word:
/a\B
/
ja
va ruby clojurescript ja
va
script
If you put \b
in front of the character we're searching for, the characters at the beginning of the word will be found:
/\bj
/
j
ava ruby clojurescript j
avascript
Using inverting again:
/\Bj
/
java ruby cloj
urescriptj
javascript
For clarity, if we compare with the previous example, we added another j
after the clojurescript
in our string. Now let's find only instances of j
that are neither at the beginning nor at the end of a word:
/\Bj\B
/
java ruby cloj
urescriptj javascript
The Hexlet support team or other students will answer you.
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