Check if a String Starts With Number Using Regular Expression

To check if a string starts with a number using a regular expression (regex), you can use a pattern that matches the beginning of the string (^) followed by any digit (\\d). Here’s how you can do this in various programming languages and environments.

Regex Pattern

The regex pattern to match a string that starts with a number is:

^\\d

• ^ asserts the position at the start of the string.
• \\d matches any digit (equivalent to [0-9]).

Examples in Different Languages

1. JavaScript

const str = "123abc";
const regex = /^\\d/;

if (regex.test(str)) {
    console.log("The string starts with a number.");
} else {
    console.log("The string does not start with a number.");
}

2. Python

import re

str = "123abc"
pattern = r'^\\d'

if re.match(pattern, str):
    print("The string starts with a number.")
else:
    print("The string does not start with a number.")

3. Java

public class Main {
    public static void main(String[] args) {
        String str = "123abc";
        String pattern = "^\\\\d";

        if (str.matches(pattern)) {
            System.out.println("The string starts with a number.");
        } else {
            System.out.println("The string does not start with a number.");
        }
    }
}

4. PHP

$str = "123abc";
$pattern = '/^\\d/';

if (preg_match($pattern, $str)) {
    echo "The string starts with a number.";
} else {
    echo "The string does not start with a number.";
}

5. C#

using System;
using System.Text.RegularExpressions;

class Program {
    static void Main() {
        string str = "123abc";
        string pattern = @"^\\d";

        if (Regex.IsMatch(str, pattern)) {
            Console.WriteLine("The string starts with a number.");
        } else {
            Console.WriteLine("The string does not start with a number.");
        }
    }
}

Summary

The regex pattern ^\\d is effective for checking if a string starts with a number across various programming languages. You can easily adapt the examples provided to fit your specific needs. This approach is useful in data validation, parsing, and processing tasks where identifying the initial character of a string is essential.

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