3v4l.org

run code in 300+ PHP versions simultaneously
<?php $strs = ['2 + 2', 'f( " ")', 'f("Test \\"mystring\\" .")', 'f("\' ", " ")']; $rx = '~(?<!\\\\)(?:\\\\{2})*(?:"[^\\\\"]*(?:\\\\.[^"\\\\]*)*"|\'[^\'\\\\]*(?:\\\\.[^\'\\\\]*)*\')(*SKIP)(*F)|\h+~s'; print_r( preg_replace($rx, '', $strs) );

preferences:
26.27 ms | 405 KiB | 5 Q