How to Check if a File Contains a String in PHP

To determine if a specific string is present within a file, let's explore a solution and a more efficient alternative.

Original Code:

The provided code attempts to check for the presence of a string in a file, denoted by the variable $id, by reading the file line-by-line. However, the condition (strpos($buffer, $id) === false) in the while loop is incorrectly checking for the absence of the string, leading to the logical negation of the desired outcome.

Improved Solution:

To rectify the situation, we can simplify the code using the file_get_contents() function, which reads the entire file into a string. Then, the strpos() function can be used to check for the presence of the $id string within this string:

if( strpos(file_get_contents("./uuids.txt"),$_GET['id']) !== false) {
    // do stuff
}

By using this approach, we avoid iterating through the file line-by-line, which can save time and memory, especially for large files.

Alternative Method (for Extremely Large Files):

For excessively large files, relying on file operations to search for a string can pose performance challenges. As an alternative, we can utilize the grep command:

if( exec('grep '.escapeshellarg($_GET['id']).' ./uuids.txt')) {
    // do stuff
}

This approach uses the system's grep utility to find the string in the file, reducing the workload on the PHP script itself while providing comparable efficiency.