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How to validate image file extension using Regular Expression
  • Last Updated : 04 Feb, 2021

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++

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// 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

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Java

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// 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));
    }
}

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Python3

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# 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

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Output: 

true
true
false
false
false

 

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