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Copyright 1991 David Jurgens |
BCB - Batch Control Block (undocumented)
DOS 2.x thru DOS 3.2 BCB Format
Offset Size Description
00 byte unknown
01 word if non-zero; segment of control block for active FOR
03 byte type of batch command
0 - normal batch command
1 - FOR-loop active
04 dword offset of next command to execute in batch file
07 word offset of variable %0 (batch file name)
09 9 words offset of %N batch file parameters, 0FFFFh indicates
parameter is null
1C nbytes null terminated path and filename of the current
batch file immediately followed by command line
parameters. Each parameter %0-%9 plus a CR is
appended and resulting string is null terminated.
DOS 3.3 BCB Format
Offset Size Description
00 byte unknown
01 byte global echo switch, if exec'd by batch CALL-command
1 - turn ECHO ON on return to calling batch file
0 - turn ECHO OFF on return to calling batch file
02 word batch file BCD segment if executed via CALL
if zero; batch file was called from command line
if non-zero; batch file executed via CALL-command
04 word if non-zero; segment of control block for active FOR
06 byte type of batch command
0 - normal batch command
1 - FOR-loop active
07 dword offset of next command to execute in batch file
0B word offset of variable %0 (batch file name)
0D 9words offset of %N batch file parameters, 0FFFFh indicates
parameter is null
1F nbytes null terminated path and filename of the current
batch file immediately followed by command line
parameters. Each parameter %0-%9 plus a CR is
appended and resulting string is null terminated.
- BCB length is variable and depends on the size and count of the
parameters and fully qualified batch file name
- the MCB for a BCB has a process Id of the transient portion of
the latest COMMAND.COM
- offsets displayed are relative to the BCB segment
- SHIFT command changes the offsets of the parameters in the table
at the offsets 0B0h thru 1Ch
- BCB of DOS 3.3 is the same as earlier versions except 3 bytes
were added after offset 0
- to find a BCB, locate the first block in the MCB chain belonging
to COMMAND.COM (the second allocated block always belongs to
COMMAND.COM). Then scan the MCB chain for a 64 byte block with
the same owner ID as COMMAND.COM). This will be the BCB.
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| Esc or Alt-X to exit |
Batch Control Block |
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