What potential issues can arise when running a PHP5 script on a PHP4 server?

When running a PHP5 script on a PHP4 server, potential issues can arise due to compatibility differences between the two versions. This can lead to syntax errors, deprecated functions, and other compatibility issues that may cause the script to not function properly. To solve this issue, it is recommended to update the PHP version on the server to at least PHP5 or modify the script to be compatible with PHP4. 

// Check PHP version and update if necessary
if (version_compare(PHP_VERSION, '5.0.0', '<')) {
    // Update PHP version
    // Or modify script to be compatible with PHP4
}

Keywords

PHP5 PHP4 backward compatibility deprecated functions compatibility issues

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