How to validate image file extension using Regular Expression

Given string str, the task is to check whether the given string is a valid image file extension or not by using Regular Expression. 

The valid image file extension must specify the following conditions: 
 

1. It should start with a string of at least one character.
2. It should not have any white space.
3. It should be followed by a dot(.).
4. It should be end with any one of the following extensions: jpg, jpeg, png, gif, bmp.

Examples: 

Input: str = "abc.png" 
Output: true 
Explanation: 
The given string satisfy all the above mentioned conditions.
Input: str = "im.jpg" 
Output: true 
Explanation: 
The given string satisfy all the above mentioned conditions.
Input: str = ".gif" 
Output: false 
Explanation: 
The given string doesn't start with image file name(required at least one character). Therefore, it is not a valid image file extension. 

Approach: This problem can be solved by using regular expression. 

• Get the String.
• Create a regular expression to check the valid image file extension as mentioned below:

regex = "([^\\s]+(\\.(?i)(jpe?g|png|gif|bmp))$)"; 

• Where: 
  
  • ( represents the starting of group 1.
  • [^\\s]+ represents the string must contain at least one character.
  • ( represents the starting of group 2.
  • \\. Represents the string should follow by a dot(.).
  • (?i) represents the string ignore the case-sensitive.
  • ( represents the starting of group3.
  • jpe?g|png|gif|bmp represents the string end with jpg or jpeg or png or gif or bmp extension.
  • ) represents the ending of the group 3.
  • ) represents the ending of the group 2.
  • $ represents the end of the string.
  • ) represents the ending of the group 1.
• Match the given string with regular expression. In Java, this can be done by using Pattern.matcher().
• Return true if the given string matched with the regular expression, else return false.

Below is the implementation of the above approach:

// C++ program to validate the
// image file extension using Regular Expression
#include <iostream>
#include <regex>
using namespace std;

// Function to validate the image file extension.
bool imageFile(string str)
{

  // Regex to check valid image file extension.
  const regex pattern("[^\\s]+(.*?)\\.(jpg|jpeg|png|gif|JPG|JPEG|PNG|GIF)$");

  // If the image file extension
  // is empty return false
  if (str.empty())
  {
     return false;
  }

  // Return true if the image file extension
  // matched the ReGex
  if(regex_match(str, pattern))
  {
    return true;
  }
  else
  {
    return false;
  }
}

// Driver Code
int main()
{
  
  // Test Case 1:
  string str1 = "abc.png";
  cout << imageFile(str1) << endl;

  // Test Case 2:
  string str2 = "im.jpg";
  cout << imageFile(str2) << endl;

  // Test Case 3:
  string str3 = ".gif";
  cout << imageFile(str3) << endl;

  // Test Case 4:
  string str4 = "abc.mp3";
  cout << imageFile(str4) << endl;

  // Test Case 5:
  string str5 = " .jpg";
  cout << imageFile(str5) << endl;

  return 0;
}

// This code is contributed by yuvraj_chandra

// Java program to check valid
// image file extension using regex

import java.util.regex.*;
class GFG {

    // Function to validate image file extension .
    public static boolean imageFile(String str)
    {
        // Regex to check valid image file extension.
        String regex
            = "([^\\s]+(\\.(?i)(jpe?g|png|gif|bmp))$)";

        // Compile the ReGex
        Pattern p = Pattern.compile(regex);

        // If the string is empty
        // return false
        if (str == null) {
            return false;
        }

        // Pattern class contains matcher() method
        // to find matching between given string
        // and regular expression.
        Matcher m = p.matcher(str);

        // Return if the string
        // matched the ReGex
        return m.matches();
    }

    // Driver code
    public static void main(String args[])
    {

        // Test Case 1:
        String str1 = "abc.png";
        System.out.println(imageFile(str1));

        // Test Case 2:
        String str2 = "im.jpg";
        System.out.println(imageFile(str2));

        // Test Case 3:
        String str3 = ".gif";
        System.out.println(imageFile(str3));

        // Test Case 4:
        String str4 = "abc.mp3";
        System.out.println(imageFile(str4));

        // Test Case 5:
        String str5 = " .jpg";
        System.out.println(imageFile(str5));
    }
}

# Python3 program to validate 
# image file extension using regex 
import re

# Function to validate 
# image file extension .  
def imageFile(str):

    # Regex to check valid image file extension.
    regex = "([^\\s]+(\\.(?i)(jpe?g|png|gif|bmp))$)"
    
    # Compile the ReGex
    p = re.compile(regex)

    # If the string is empty 
    # return false
    if (str == None):
        return False

    # Return if the string 
    # matched the ReGex
    if(re.search(p, str)):
        return True
    else:
        return False

# Driver code

# Test Case 1:
str1 = "abc.png"
print(imageFile(str1))

# Test Case 2:
str2 = "im.jpg"
print(imageFile(str2))

# Test Case 3:
str3 = ".gif"
print(imageFile(str3))

# Test Case 4:
str4 = "abc.mp3"
print(imageFile(str4))

# Test Case 5:
str5 = " .jpg"
print(imageFile(str5))

# This code is contributed by avanitrachhadiya2155

// C# program to validate the
//image file extension 
//using Regular Expressions
using System;
using System.Text.RegularExpressions;
class GFG
{

  // Main Method
  static void Main(string[] args)
  {

    // Input strings to Match
    //image file extension  
    string[] str={"abc.png","im.jpg",".gif","abc.mp3"," .jpg"};
    foreach(string s in str) {
      Console.WriteLine( imageFile(s) ? "true" : "false");
    }
    Console.ReadKey(); }

  // method containing the regex
  public static bool imageFile(string str)
  {
    string strRegex = @"([^\s]+(\.(?i)(jpe?g|png|gif|bmp))$)";
    Regex re = new Regex(strRegex);
    if (re.IsMatch(str))
      return (true);
    else
      return (false);
  }
}

// This code is contributed by Rahul Chauhan

// Javascript program to validate
// Image File using Regular Expression

// Function to validate the
// Image File
function imageFile(str) {
    // Regex to check valid
    // Image File
    let regex = new RegExp(/[^\s]+(.*?).(jpg|jpeg|png|gif|JPG|JPEG|PNG|GIF)$/);

    // if str
    // is empty return false
    if (str == null) {
        return "false";
    }

    // Return true if the str
    // matched the ReGex
    if (regex.test(str) == true) {
        return "true";
    }
    else {
        return "false";
    }
}

// Driver Code
// Test Case 1:
let str1 = "abc.png";
console.log(imageFile(str1));

// Test Case 2:
let str2 = "im.jpg";
console.log(imageFile(str2));

// Test Case 3:
let str3 = ".gif";
console.log(imageFile(str3));

// Test Case 4:
let str4 = "abc.mp3";
console.log(imageFile(str4));

// Test Case 5:
let str5 = " .jpg";
console.log(imageFile(str5));


// This code is contributed by Rahul Chauhan

true
true
false
false
false

Time Complexity: O(N) for each testcase, where N is the length of the given string. 
Auxiliary Space: O(1)