The following options are in general not needed for the normal operation of GAP. They are mostly used for debugging.
-a memory
GASMAN, the storage manager of GAP uses sbrk to get blocks of memory
from (certain) operating systems and it is required that subsequent calls
to sbrk produce adjacent blocks of memory in this case because GAP
only wants to deal with one large block of memory. If the C function
malloc is called for whatever reason, it is likely that sbrk will no
longer produce adjacent blocks, therefore GAP does not use malloc itself.
However some operating systems insist on calling malloc to create a
buffer when a file is opened, or for some other reason. In order to
catch these cases GAP preallocates a block of memory with malloc
which is immediately freed. The amount preallocated can be controlled
with the -a option. If the last character of memory is k or K
it is taken as KBytes and if the last character is m or M memory
is taken as MBytes.
'-A'
By default, some share packages (see Share Packages) are loaded, if present, into the GAP session when it starts. This option disables (actually toggles) this behaviour, which can be useful for debugging or testing.
'-B architecture'
Execuable binary files that form part of GAP or of a share package are kept in a subdirectory of the 'bin' dirctory with in the GAP or package root directory. The subdirectory name is determined from the operating system, processor and compiler details when GAP (resp. the package) is installed. Under rare circumstances, it may be necessary to override this name, and this can be done using the '-B' option.
-D
The -D option tells GAP to print short messages when it is reading
or completing files or loading modules.
#I READ_GAP_ROOT: loading 'lib/kernel.g' as GAP file
tells you that GAP has started to read the library file ``lib/kernel.g''.
#I READ_GAP_ROOT: loading 'lib/kernel.g' statically
tells you that GAP has used the compiled version of the library file ``lib/kernel.g''. This compiled module was statically linked to the GAP kernel at the time the kernel was created.
#I READ_GAP_ROOT: loading 'lib/kernel.g' dynamically
tells you that GAP has loaded the compiled version of the library file
``lib/kernel.g''. This compiled module was dynamically loaded to the
GAP kernel at runtime from a corresponding .so file.
#I completing 'lib/domain.gd'
tells you that GAP has completed the file ``lib/domain.gd''. See Completion Files for more information about completion of files.
-M
The -M option tells GAP not to check for, nor to use, compiled
versions of library files.
-N
The -N option tells GAP not to check for, nor to use, completion
files, see Completion Files.
'-O'
The '-O' option enables a GAP 3 compatibility mode, in which (for instance) the values 'false' and 'fail' are identified. Use of this mode is not recommended other than as a transitional step in porting GAP 3 code to GAP 4, because the GAP 4 library may not work reliably in this mode.
'-T'
The '-T' option suppresses the usual break loop behaviour of GAP. With this option GAP behaves as if the user 'quit' immediately from every break loop. This is intended for automated testing of GAP.
-X
The -X option tells GAP to do a consistency check of the library
file and the corresponding completion file when reading the completion
file.
-Y
The -Y option tells GAP to do a consistency check of the library
file and the corresponding completion file when completing the library
file.
-i filename
The -i changes the name of the init file from the default ``init.g'' to
filename.
Additional options, '-C', '-U', '-P', '-W' amd '-z' are used internally in the GAP compiler and/or on specific operating systems.
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GAP 4 manual