These commands provide a facility to scan files, matching lines of the file against regular expressions and executing Tcl code on a match. With this facility you can use Tcl to do the sort of file processing that is traditionally done with awk. And since Tcl's approach is more declarative, some of the scripts that can be rather difficult to write in awk are simple to code in Tcl.
File scanning in Tcl centers around the concept of a scan context. A scan context contains one or more match statements, which associate regular expressions to scan for with Tcl code to be executed when the expressions are matched.
See the manual pages for the following commands: