Debug (command)

Infobox Software
name = Debug
author = Tim Paterson
developer = Microsoft
operating system = DOS, MS-DOS, OS/2, Microsoft Windows
genre = Debugger
website = [http://technet.microsoft.com/en-us/library/bb491040.aspx Debug]

debug is a command in DOS, MS-DOS, OS/2 and Microsoft Windows which runs the program debug.exe (or DEBUG.COM in older versions of DOS).cite web| author=Daniel B. Sedory|title=A Guide to DEBUG|accessdate=2007-05-25|url=http://mirror.href.com/thestarman/asm/debug/debug.htm|] Debug can act as an assembler, disassembler, or hex dump program allowing users to interactively examine memory contents (in assembly language, hexadecimal or ASCII), make changes, and selectively execute COM, EXE and other file types. It also has several subcommands which are used to access specific disk sectors, I/O ports and memory addresses. MS-DOS Debug runs at a 16-bit process level and therefore it is limited to 16-bit computer programs. FreeDOS Debug has a "DEBUGX" version supporting 32-bit DPMI programs as well.cite web|url=http://japheth.de/Debug/README.TXT|title=FreeDOS DEBUG README|date=|accessdate= 2007-06-25|author=Paul Vojta]

Background

Traditionally, all computers and operating systems have included a maintenance function, used to determine whether a program is working correctly.Fact|date=June 2007 Debug was written by Tim Paterson to serve this purpose in QDOS. When Paterson began working for Microsoft in the early 1980s he brought the program with him. Debug was part of DOS 1.00 and has been included in MS-DOS and Microsoft Windows. MS-DOS debug has several limitations:

* It can only access 16-bit registers and not 32-bit extended registers.
* When the "n" subcommand for naming files is used the filename is stored from offset DS:5D to DS:67 meaning that the program can only save files in FAT12 format.
* MS-DOS Debug can only access conventional memory, which is the first 640K in an IBM PC.

32-bit Debug clones, such as FreeDOS Debug, have been written.

yntax

debug [Drive:] [Path] FileName [parameters]

When Debug is started without any parameters the Debug prompt, a "-", appears. The user can then enter one of several one or two-letter subcommands, including "a" to enter the assembler mode, "d" to perform a hexadecimal dump, "t" to trace and "u" to unassemble (disassemble) a program in memory. [cite web|title=Microsoft TechNet Debug article|url=http://technet.microsoft.com/en-us/library/bb491040.aspx|accessdate=2008-04-23] Debug can also be used as a "debug script" interpreter using the following syntax.

debug < FileName

A script file may contain Debug subcommands and assembly language instructions.cite web|title=Using Debug|url=http://kipirvine.com/asm/debug/Debug_Tutorial.pdf|accessdate=2007-06-23] This method can be used to create or edit binary files from batch files.

ee also

* List of DOS commands
* Edlin is another DOS tool written by Tim Paterson.
* SoftICE a modern debugger that inherited its syntax from DebugFact|date=June 2007

References

External links

* [http://mirror.href.com/thestarman/asm/debug/debug.htm A Guide to DEBUG]
* [http://www.computerhope.com/debughlp.htm Information about the debug command]
* [http://www.computerhope.com/rdebug.htm Computer Debug Routines / Machine Code]
* [http://help.fdos.org/en/hhstndrd/debug.htm] , [http://japheth.de/Debug/README.TXT] FreeDOS Debug