3v4l.org

run code in 300+ PHP versions simultaneously
<?php foreach ( array( array('/\\d+/', '$0'), array('/\\d+/', '$01'), array('/\\d+/', '${0}1'), array('/(\\d+)/', '$0'), array('/(\\d+)/', '$01'), array('/(\\d+)/', '{$0}1'), array('/(\\d+)/', '$1'), array('/(\\d+)/', '$12'), array('/(^)(^)(^)(^)(^)(^)(^)(^)(^)(^)(^)(\\d+)/', '$12'), array('/(^)(^)(^)(^)(^)(^)(^)(^)(^)(^)(^)(\\d+)/', '$123'), ) as $list ) { list ($re, $replace) = $list; echo "$re '$replace' => '", preg_replace($re, $replace, "42"), "'\n"; }
Output for 4.3.0 - 4.3.11, 4.4.0 - 4.4.9, 5.0.0 - 5.0.5, 5.1.0 - 5.1.6, 5.2.0 - 5.2.17, 5.3.0 - 5.3.29, 5.4.0 - 5.4.45, 5.5.0 - 5.5.38, 5.6.0 - 5.6.30, 7.0.0 - 7.0.20, 7.1.0 - 7.1.33, 7.2.17 - 7.2.33, 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.27, 8.2.0 - 8.2.17, 8.3.0 - 8.3.4
/\d+/ '$0' => '42' /\d+/ '$01' => '' /\d+/ '${0}1' => '421' /(\d+)/ '$0' => '42' /(\d+)/ '$01' => '42' /(\d+)/ '{$0}1' => '{42}1' /(\d+)/ '$1' => '42' /(\d+)/ '$12' => '' /(^)(^)(^)(^)(^)(^)(^)(^)(^)(^)(^)(\d+)/ '$12' => '42' /(^)(^)(^)(^)(^)(^)(^)(^)(^)(^)(^)(\d+)/ '$123' => '423'

preferences:
298.89 ms | 406 KiB | 392 Q