Subversion Repositories SvarDOS

                    === SvarCOM implementation notes ===


=== SWAPPING =================================================================

While conventional RAM is scarce, a command line interpreter must make effort
to reduce its memory footprint when launching applications. SvarCOM does that
by installing a small executable module in memory, called RMOD (for Resident
MODule). SvarCOM pre-sets RMOD so knows how to execute the external program
and removes itself from memory, letting RMOD do the job. RMOD executes the
application, waits for it to finish and then calls back SvarCOM.


=== NLS strings ==============================================================

SvarCOM can output information in many languages. To do so, it relies on a
precompiled resource file named SVARCOM.LNG. When SvarCOM starts, it looks
for this file in the %NLSPATH% directory and loads from it the part that
contains the %LANG% language. All this is done by nls_langreload().

The SVARCOM.LNG file is compiled by a separate tool: TLUMACZ. It takes
CATS-style language files as input and compiles them into a single SVARCOM.LNG
resource file. It also produces a DEFAULT.LNG with english strings only, this
one is embedded into the SvarCOM executable to display english text in case
SVARCOM.LNG is unavailable.


=== Batch files support ======================================================

When SvarCOM executes a command, it checks first if it has a *.BAT extension.
If so, it switches into 'batch-processing' mode:

 - Writes the batch filename into its persistent (rmod-owned) buffer, along
   with a line counter that holds the number of "next line to be executed".
 - When a batch file CALLs another batch file, then a new SvarCOM instance is
   started. This ensures that once the CALLed batch ends, processing will
   return to the original batch file at the correct position.

When the batch buffer is non-zero, SvarCOM does not ask the user for a
command. Instead, it opens the batch file, jumps to the "next line to be
executed" and loads the command from there, incrementing this counter in the
process. The maximum length of a batch file is of 65535 lines (any lines after
this limit will be ignored).


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