Source file display and manipulation

The sdb program is designed to make it easy to debug a program without constant reference to a current source listing. Facilities are provided that perform context searches within the source files of the program being debugged and display selected portions of the source files. The commands are similar to those of the UNIX system text editor, ed(C). Like the editor, sdb has a notion of current file and line within the current file. The sdb program also knows how the lines of a file are partitioned into functions, so it also has a notion of current function.