We have seen that, we are using *, +, ., $, etc for different purposes. Now, if we want to match them themselves, we have to escape them using escape character(backslash-\) .
Below is the table for these kind of characters and their escaped version, along with their usages.
| Character | Usage | Escaped version | |
| \ | escape character | \\ | |
| . | predefined character class | \. | |
| | | OR operator | \\ | |
| * | as quantifier | \* | |
| + | as quantifier | \+ | |
| ? | as quantifier | \? | |
| ^ | boundary matcher | \^ | |
| $ | boundary matcher | \$ | |
| { | in quantifier notation | \{ | |
| } | in quantifier notation | \} | |
| [ | in character class notation | \[ | |
| ] | in character class notation | \] | |
| ( | in group notation | \( | |
| ) | in group notation | \) | |
| - | range operator | NA |
Sometimes, it is also preferred to use escaped forward slash(/).
Predict the output of the following regex:
RegEx: \b(0|(1(01*0)*1))*\b
Text: This RegEx denotes the set of binary numbers divisible by 3:
0,11,1010, 1100, 1111, 1001
Answer:
Find a regular expression to match whole lines in the text containing either Apple, Orange, Grape as a word.
Hint: Use ^ and $ to match whole lines.
Answer: ^.*\b(apple|orange|grape)\b.*$
Find an expression which matches cat., 896., ?=++ but not abc1.
Answer: ...\W