While filling online forms, haven't you come across errors like "Please enter valid email address" or "Please enter valid phone number".
- -Annoying as they may be, there's a lot of black magic that the computer does before it determines that, the details you've entered are incorrect.
- -Can you think out, what is that black magic? If you are familiar with algorithms, then you will say that we can write an algorithm for the same.
- -Yes, we can write an algorithm to verify different things, but we have a standard tool designed for similar kinds of purposes.
- -It is Regular Expression. We call it RegEx for short. RegEx makes our work a lot easier. Let's see some basic examples where RegEx becomes handy.
- -Suppose, you are in search of an averge price of a particular product on amazon. The following regular expression will find you any price(ex. $12, $75.50) on the webpage: \$([0-9]+)\.([0-9]+). In the Image below, yellowish part shows the matched prices.
Quite interesting!
- -Let's look at another example. You have a long list of documents with different kinds of extensions. You are particularly looking for data files having .dat extension.
- -^.*\.dat$ is a regular expression which represents a set of string ending with .dat. Regular expression is a standardized way to encode such patterns.
Below in the image, you can see that all three files having .dat extension are extracted from the list of five files.
- -Well. What does the name Regular Expression(RegEx) represent? Regular Expression represents the sequence of characters that defines a regular search pattern.
- -RegEx is a standardized tool to do the following works:
- -We are going to look at all the three things above.
- -Let's begin the journey with RegEx!
- -Note:
- -In this article series, we are going to show all examples using live interactive playground, so that you can play with regex. You can activate playground by just clicking on it.
- -Simple matching of a specific word can be done as following:
- -As you can see it matches "Reg" in the text. Similarly, what will be the match for "Ex" in the same text above?
- -Do you notice anything? It is a case sensitive.
- -Most of the programming languages have libraries for RegEx. They have almost similar kind of syntax. Here, we will see how to implement it in Javascript.
- -Below is a basic code in Javascript, showing how to implement regex. The patterns are written in /_____/g. Where g is a modifier, which is used to find all matches rather than stopping at the first match.
The function exec returns null, if there is no match and match data otherwise.
- -
// Main text (string) in which we are finding
-// Patterns
-var str = "RegEx stands for Regular Expression!";
-
-// Pattern string
var pattern = /Reg/g;
-// This will print all the data of matches
-// across the whole string
-while(result = pattern.exec(str))
-{
- console.log(result); // printing
+// This will print all the data of matches across the whole string
+while(result = pattern.exec(text_to_search_in)) {
+ console.log(result);
}
-
-// This will be the output
-/*
-[
+[
'Reg',
index: 0,
input: 'RegEx stands for Regular Expression!',
@@ -139,11 +108,15 @@ while(result = pattern.exec(str))
input: 'RegEx stands for Regular Expression!',
groups: undefined
]
-*/
Note: Groups in the above output is a RegEx concept.
-Note: Groups in the above output is a RegEx concept.
- - - + +