$number | Substitutes the substring matched by group number. |
${name} | Substitutes the substring matched by a named group name. |
$$ | Escaped '$' character in the result (replacement) string. |
$& ($0) | Replaces with the whole matched string. |
$+ ($&) | Substitutes the matched text to the last group captured. |
$` | Substitutes all the matched text with every non-matched text before the match. |
$' | Substitutes all the matched text with every non-matched text after the match. |
$_ | Substitutes all the matched text to the entire string. |
Note: | Italic terms means the strings are volatile (May vary depending on your regex flavor). |