php code shell_exec to seach all files in all directories and replace old text with a new text

Here is an example of using the shell_exec function in PHP to search all files in all directories and replace old text with new text:

<?php
// Define the old and new text strings
$oldText = "Hello";
$newText = "Goodbye";

// Use the shell_exec function to search all files in all directories for the old text string and replace it with the new text string
$output = shell_exec('grep -rl "' . $oldText . '" /path/to/directory | xargs sed -i "s/' . $oldText . '/' . $newText . '/g"');

// Output the results
echo $output;
?>

In this example, the grep command is used to recursively search for all files in the specified directory that contain the old text string. The xargs command is used to pass the list of files to the sed command, which is used to replace the old text string with the new text string in each file.

Note that this is just an example, and you should modify it to fit your specific needs. Make sure to test the code thoroughly before using it on important files.