StringCases

StringCases["string",patt] gives a list of the substrings in "string" that match the string expression patt. 

StringCases["string",lhs->rhs] gives a list of the values of rhs corresponding to the substrings that match the string expression lhs. 

StringCases["string",p,n] includes only the first n substrings that match. 

StringCases["string",{p1,p2,…}] gives substrings that match any of the pi. 

StringCases[{s1,s2,…},p] gives the list of results for each of the si. 

StringCases[patt] represents an operator form of StringCases that can be applied to an expression.

Please visit the official Wolfram Language Reference for more details and examples on core symbols.