prevents theme activation on a server that's PHP version is below 5.6.

php-version-stop.php

<?php

/**
 * Set a constant that holds the theme's minimum supported PHP version.
 */
define( 'THEMESLUG_MIN_PHP_VERSION', '5.6' );

/**
 * Immediately after theme switch is fired we we want to check php version and
 * revert to previously active theme if version is below our minimum.
 */
add_action( 'after_switch_theme', 'themeslug_test_for_min_php' );

/**
 * Switches back to the previous theme if the minimum PHP version is not met.
 */
function themeslug_test_for_min_php() {

	// Compare versions.
	if ( version_compare( PHP_VERSION, THEMESLUG_MIN_PHP_VERSION, '<' ) ) {
		// Site doesn't meet themes min php requirements, add notice...
		add_action( 'admin_notices', 'themeslug_min_php_not_met_notice' );
		// ... and switch back to previous theme.
		switch_theme( get_option( 'theme_switched' ) );
		return false;

	};
}

/**
 * An error notice that can be displayed if the Minimum PHP version is not met.
 */
function themeslug_min_php_not_met_notice() {
	?>
	

		


			


	<?php
}