ast-grep is an abstract syntax tree based tool to search code by
pattern code. Think of it as your old-friend grep, but matching AST
nodes instead of text. You can write patterns as if you are writing
ordinary code. It will match all code that has the same syntactical
structure. You can use $ sign + upper case letters as a wildcard,
e.g. $MATCH, to match any single AST node. Think of it as regular
expression dot ., except it is not textual.