Regular Expressions Language Elements

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Substitutions are allowed only within replacement patterns. For similar functionality within regular expressions, use a backreference ( for example, \1 ). For details on backreferences, see Backreferences and Backreference Constructs.

Character escapes and substitutions are the only special constructs recognized in a replacement pattern. All the syntactic constructs described in the following sections are allowed only in regular expressions; they are not recognized in replacement patterns. For example, the replacement pattern a*${txt}b inserts the string a* followed by the substring matched by the "txt" capturing group, if any, followed by the string "b". The * character is not recognized as a metacharacter within a replacement pattern. Similarly, $ patterns are not recognized within regular expression matching patterns. Within regular expressions, $ designates the end of the string. For example:

Character	Meaning
$123	Substitutes the last substring matched by group number 123 ( decimal ).
${name}	Substitutes the last substring matched by a ( ?<name> ) group.

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