tool to search a file for structured pattern

 A tool for searching text files and filtering text streams for structured
 criteria. Sgrep implements a query language based on so called region
 expressions.
 .
 Like grep, sgrep can be used for any kind of text files. However it is most
 useful for text files containing some kind of structured text. A file
 containing structured text could be defined as a file, which obeys some syntax.
 Examples of structured text files are SGML, HTML, C, TeX and mail files.