Running NASM

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

This section describes the command-line parameters provided by NASM. NASM's list of parameters shows up here alphabetically. An alphabetical menu exists under each parameter heading to make things easier.

Note: No attempt at differentiating which parameter works with which version currently exists.

NASM Command-Line -a
(Disable Preprocessing)

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

If NASM is being used as the back end to a compiler, it might be desirable to suppress preprocessing completely and assume the compiler has already done it, to save time and increase compilation speeds. The -a option, requiring no argument, instructs NASM to replace its powerful preprocessor with a stub preprocessor which does nothing.

NASM Command-Line -d
(Pre-Define A Macro)

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

Just as the -p option gives an alternative to placing %include directives at the start of a source file, the -d option gives an alternative to placing a %define directive. You could code

nasm myfile.asm -dFOO=100

as an alternative to placing the directive

%define FOO 100

at the start of the file. You can miss off the macro value, as well: the option -dFOO is equivalent to coding %define FOO. This form of the directive may be useful for selecting assembly-time options which are then tested using %ifdef, for example -dDEBUG.

For Makefile compatibility with many C compilers, the compiler also accepts -D.

NASM Command-Line -E
(Send Errors To File)

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

Under MS-DOS it can be difficult (though there are ways) to redirect the standard-error output of a program to a file. Since NASM usually produces its warning and error messages on stderr, this can make it hard to capture the errors if (for example) you want to load them into an editor.

NASM therefore provides the -E option, taking a filename argument which causes errors to be sent to the specified files rather than standard error. Therefore you can redirect the errors into a file by typing

nasm -E myfile.err -f obj myfile.asm

NASM Command-Line -e
(Preprocess Only)

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

NASM allows the preprocessor to be run on its own, up to a point. Using the -e option (which requires no arguments) will cause NASM to preprocess its input file, expand all the macro references, remove all the comments and preprocessor directives, and print the resulting file on standard output (or save it to a file, if the -o option is also used).

This option cannot be applied to programs which require the preprocessor to evaluate expressions which depend on the values of symbols: so code such as

%assign tablesize ($-tablestart)

will cause an error in preprocess-only mode.

NASM Command-Line -F
(Select Debug Format)

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

This option is used to select the format of the debug information emitted into the output file, to be used by a debugger (or will be). Use of this switch does not enable output of the selected debug info format. Use -g, see NASM Command Line g, to enable output.

A complete list of the available debug file formats for an output format can be seen by issuing the command nasm -f <format> -y. (only "borland" in "-f obj", as of 0.98.35, but "watch this space") See: NASM Command Line y.

This should not be confused with the "-f dbg" output format option which is not built into NASM by default. For information on how to enable it when building from the sources, see section 6.10

NASM Command-Line -f
(Output File Format)

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

If you do not supply the -f option to NASM, it will choose an output file format for you itself. In the distribution versions of NASM, the default is always bin; if you've compiled your own copy of NASM, you can redefine OF_DEFAULT at compile time and choose what you want the default to be.

Like -o, the intervening space between -f and the output file format is optional; so -f elf and -felf are both valid.

A complete list of the available output file formats can be given by issuing the command nasm -hf.

To assemble a file, you issue a command of the form

nasm -f <format> <filename> [-o <output>]

For example,

nasm -f elf myfile.asm

Assembles myfile.asm into an ELF object file myfile.o. And

nasm -f bin myfile.asm -o myfile.com

Assembles myfile.asm into a raw binary file myfile.com.

To produce a listing file, with the hex codes output from NASM displayed on the left of the original sources, use the -l option to give a listing file name, for example:

nasm -f coff myfile.asm -l myfile.lst

-f aout / -faout

General

Linux

a.out BSD a.out bin86 ELF32 ELF64

Microsoft

COFF OMF Win32 Win64

MacIntosh

NeXTStep OpenStep Rhapsody Darwin OS X

Use aout to create a Linux a.out object file. Use the ELF32 and ELF64 formats unless a specific requirement exists for a.out.

nasm -faout HelloWorld.s

To get a list of debug types available for an aout compile:

nasm -faout -y

Version 0.98.39 replies:

valid debug formats for 'aout' output format are ('*' denotes default):
  * null      Null debug format

-f aoutb / -faoutb

General

Linux

a.out BSD a.out bin86 ELF32 ELF64

Microsoft

COFF OMF Win32 Win64

MacIntosh

NeXTStep OpenStep Rhapsody Darwin OS X

Use aoutb to create a Linux a.out object file for NetBSD/FreeBSD operating systems. Consider using the ELF32 or ELF64 object formats in place of this one.

nasm -faoutb HelloWorld.s

To get a list of debug types available for an aoutb compile:

nasm -faoutb -y

Version 0.98.39 replies:

valid debug formats for 'aoutb' output format are ('*' denotes default):
  * null      Null debug format

-f as86 / -fas86

General

Linux

a.out BSD a.out bin86 ELF32 ELF64

Microsoft

COFF OMF Win32 Win64

MacIntosh

NeXTStep OpenStep Rhapsody Darwin OS X

Use as86 to create a Linux bin86 object file (bin86 version 0.3).

nasm -fas86 HelloWorld.s

For a list of debug formats available for the bin86 type:

nasm -fas86 -y

Version 0.98.39 replies:

valid debug formats for 'as86' output format are ('*' denotes default):
  * null      Null debug format

-f bin / -fbin

General

Linux

a.out BSD a.out bin86 ELF32 ELF64

Microsoft

COFF OMF Win32 Win64

MacIntosh

NeXTStep OpenStep Rhapsody Darwin OS X

Use bin to create a flat object file.

To create an MS-DOS .com file...

nasmw.exe -fbin -oHelloWorld.com HelloWorld.asm

For a list of debug types available for a bin compile:

nasmw.exe -fbin -y

Version 0.98.39 replies:

valid debug formats for 'bin' output format are ('*' denotes default):
  * null      Null debug format

-f coff / -fcoff

General

Linux

a.out BSD a.out bin86 ELF32 ELF64

Microsoft

COFF OMF Win32 Win64

MacIntosh

NeXTStep OpenStep Rhapsody Darwin OS X

Use coff to create a COFF (i386) file.

nasmw.exe -fcoff HelloWorld.asm

For a list of debug formats available for the COFF type:

nasmw.exe -fcoff -y

Version 0.98.39 replies:

valid debug formats for 'coff' output format are ('*' denotes default):
  * null      Null debug format

-f elf / -felf / -f elf32 / -felf32

General

Linux

a.out BSD a.out bin86 ELF32 ELF64

Microsoft

COFF OMF Win32 Win64

MacIntosh

NeXTStep OpenStep Rhapsody Darwin OS X

Use elf to create an ELF32 (or ELF) file. This format replaced the Linux a.out format and most versions of Linux today run files of this type. Create this type of file to create a shared library or executable.

nasm -felf HelloWorld.s

For a list of debug formats available for the ELF/ELF32 type:

nasmw.exe -felf -y

Version 0.98.39 replies:

valid debug formats for 'elf' output format are ('*' denotes default):
  * stabs     ELF32 (i386) stabs debug format for Linux

-f elf64 / -felf64

General

Linux

a.out BSD a.out bin86 ELF32 ELF64

Microsoft

COFF OMF Win32 Win64

MacIntosh

NeXTStep OpenStep Rhapsody Darwin OS X

Use elf64 to create an ELF64 file. This parameter requires and provides a way to compile for 64-bit Linux.

nasm -felf64 HelloWorld.s

To get a list of debug options available for an ieee compile:

nasmw.exe -felf64 -y

Version 0.98.39 replies:

nasm: fatal: unrecognised output format 'elf64' - use -hf for a list
type 'nasm -h' for help

-f ieee / -fieee

General

Linux

a.out BSD a.out bin86 ELF32 ELF64 RDF

Microsoft

COFF OMF Win32 Win64

MacIntosh

NeXTStep OpenStep Rhapsody Darwin OS X

Use ieee to create an IEEE-695 (LADsoft variant) file.

nasm -fieee HelloWorld.s

To get a list of debug options available for an ieee compile:

nasmw.exe -fieee -y

Version 0.98.39 replies:

valid debug formats for 'ieee' output format are ('*' denotes default):
  * ladsoft   LADsoft Debug Records
    null      Null debug format

-f rdf / -frdf

General

Linux

a.out BSD a.out bin86 ELF32 ELF64 RDF

Microsoft

COFF OMF Win32 Win64

MacIntosh

NeXTStep OpenStep Rhapsody Darwin OS X

Use rdf to create a Linux RDF (Relocatable Dynamic Format 2.0) file.

nasm -frdf HelloWorld.s

To get a list of debug options available for an rdf compile:

nasmw.exe -frdf -y

Version 0.98.39 replies:

valid debug formats for 'rdf' output format are ('*' denotes default):
  * null      Null debug format

-f macho / -fmacho

General

Linux

a.out BSD a.out bin86 ELF32 ELF64

Microsoft

COFF OMF Win32 Win64

MacIntosh

NeXTStep OpenStep Rhapsody Darwin OS X

Use macho to create a NeXTstep, OpenStep, Rhapsody, Darwin MacOS X object file.

nasm -fmacho HelloWorld.s

To get a list of available debug formats for a Mach-o compile:

nasmw.exe -fmacho -y

Version 0.98.39 replies:

nasm: fatal: unrecognised output format 'macho' - use -hf for a list
type 'nasm -h' for help

-f obj / -fobj

General

Linux

a.out BSD a.out bin86 ELF32 ELF64

Microsoft

COFF OMF Win32 Win64

MacIntosh

NeXTStep OpenStep Rhapsody Darwin OS X

Use obj to create Microsoft 16-bit/32-bit OMF files.

nasm -fobj HelloWorld.asm

To get a list of debug types available in compiling an obj file:

nasmw.exe -fobj -y

Version 0.98.39 responds with:

valid debug formats for 'obj' output format are ('*' denotes default):
  * borland   Borland Debug Records
    null      Null debug format

-f win32 / -fwin32

General

Linux

a.out BSD a.out bin86 ELF32 ELF64

Microsoft

COFF OMF Win32 Win64

MacIntosh

NeXTStep OpenStep Rhapsody Darwin OS X

Use win32 to create a Microsoft Win32 object file.

nasmw.exe -fwin32 HelloWorld.asm

To get a list of debug types available for a win32 compile:

nasmw.exe -fwin32 -y

Version 0.98.39 responds with:

valid debug formats for 'win32' output format are ('*' denotes default):
  * null      Null debug format

-f win64 / -fwin64

General

Linux

a.out BSD a.out bin86 ELF32 ELF64

Microsoft

COFF OMF Win32 Win64

MacIntosh

NeXTStep OpenStep Rhapsody Darwin OS X

Use win64 to create a Microsoft Win64 object file.

nasmw.exe -fwin64 HelloWorld.asm

To get a list of debug types available for a win64 compile:

nasmw.exe -fwin64 -y

Version 0.98.39 responds with:

nasm: fatal: unrecognised output format 'win64' - use -hf for a list
type 'nasm -h' for help

NASM Command-Line -g
(Enable Debug Details)

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

This option can be used to generate debugging information in the specified format. See: NASM Command Line F. Using -g without -F results in emitting debug info in the default format, if any, for the selected output format. If no debug information is currently implemented in the selected output format, -g is silently ignored.

NASM Command-Line -h
(Help)

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

To get further usage instructions from NASM, type

nasm -h

nasmw -h

NASM Command-Line -hf (Help File Formats)

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

The -hf command-line parameter lists the available output file formats.

Linux systems come in two flavors: a.out or ELF. To determine your flavor of Linux, type

file nasm

(in the directory where you installed the NASM binary). If it says something like

nasm: ELF 32-bit LSB executable i386 (386 and up) Version 1

then your system is ELF, so use the -f elf option to produce Linux object files.

If it says

nasm: Linux/i386 demand-paged executable (QMAGIC)

or something similar, your system is a.out. Use -f aout to produce your Linux object files. Linux a.out systems end up obsolete and rare.

Like Unix compilers and assemblers, NASM remains silent unless something goes wrong. You see no output, unless NASM encounters a problem.

On a Windows system, NASM displays the following:

Z:\nasm\nasm64\bin>nasm64.exe -hf
...
valid output formats for -f are ('*' denotes default):
  * bin       Flat-form binary (e.g. DOS .COM, .SYS)
    aout      Linux a.out object file
    aoutb     NetBSD/FreeBSD a.out object file
    coff      COFF (i386) (e.g. DJGPP for DOS)
    elf       ELF32 (i386) object file (e.g. Linux)
    elf64     ELF64 (i386) object file (e.g. Linux)
    as86      Linux bin86 (version 0.3) object file
    obj       MS-DOS 16-bit/32-bit OMF
    win32     Microsoft Win32 (i386) COFF
    win64     Microsoft Win64 (i386) COFF
    rdf       Relocatable dynamic file v2.0
    ieee      IEEE-695 (LADsoft variant) format
    macho     NeXTSTEP/OpenStep/Rhapsody/Darwin/MacOS X file

NASM Command-Line -i
(Include File Search Directories)

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

When NASM sees the %include or the INCBIN directive in a source file (see section 4.6 or INCBIN directive), it will search for the given file not only in the current directory, but also in any directories specified on the command line by the use of the -i option. Therefore you can include files from a macro library, for example, by typing

nasm -ic:\macrolib\ -f obj myfile.asm

(As usual, a space between -i and the path name is allowed, and optional).

NASM, in the interests of complete source-code portability, does not understand the file naming conventions of the OS it is running on; the string you provide as an argument to the -i option will be prepended exactly as written to the name of the include file. Therefore the trailing backslash in the above example is necessary. Under Unix, a trailing forward slash is similarly necessary.

(You can use this to your advantage, if you're really perverse, by noting that the option -ifoo will cause %include "bar.i" to search for the file foobar.i...)

If you want to define a standard include search path, similar to /usr/include on Unix systems, you should place one or more -i directives in the NASMENV environment variable.

For Makefile compatibility with many C compilers, this option can also be specified as -I.

NASM Command-Line -l
(Generate Listing File)

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

If you supply the -l option to NASM, followed (with the usual optional space) by a file name, NASM will generate a source-listing file for you, in which addresses and generated code are listed on the left, and the actual source code, with expansions of multi-line macros (except those which specifically request no expansion in source listings: see section 4.3.9) on the right. For example:

nasm -f elf myfile.asm -l myfile.lst

If a list file is selected, you may turn off listing for a section of your source with [list -], and turn it back on with [list +], (the default, obviously). There is no "user form" (without the brackets). This can be used to list only sections of interest, avoiding excessively long listings.

NASM Command-Line -M
(Generate Makefile Dependencies)

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

This option can be used to generate makefile dependencies on stdout. This can be redirected to a file for further processing. For example:

NASM -M myfile.asm > myfile.dep

NASM Command-Line -On
(Specify Multipass Optimization)

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

NASM defaults to being a two pass assembler. This means that if you have a complex source file which needs more than 2 passes to assemble optimally, you have to enable extra passes.

Using the -O option, you can tell NASM to carry out multiple passes. The syntax is:

-O0 strict two-pass assembly, JMP and Jcc are handled more like v0.98, except that backward JMPs are short, if possible. Immediate operands take their long forms if a short form is not specified.
-O1 strict two-pass assembly, but forward branches are assembled with code guaranteed to reach; may produce larger code than -O0, but will produce successful assembly more often if branch offset sizes are not specified. Additionally, immediate operands which will fit in a signed byte are optimised, unless the long form is specified.
-On multi-pass optimization, minimize branch offsets; also will minimize signed immediate bytes, overriding size specification unless the strict keyword has been used (see section 3.7). The number specifies the maximum number of passes. The more passes, the better the code, but the slower is the assembly.

Note that this is a capital O, and is different from a small o, which is used to specify the output format. See NASM Command Line o.

NASM Command-Line -o
(Output File Name)

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

NASM normally chooses the name of your output file for you; precisely how it does this is dependent on the object file format. For Microsoft object file formats (obj and win32), it will remove the .asm extension (or whatever extension you like to use - NASM doesn't care) from your source file name and substitute .obj. For Unix object file formats (aout, coff, elf and as86) it will substitute .o. For rdf, it will use .rdf, and for the bin format it will simply remove the extension, so that myfile.asm produces the output file myfile.

If the output file already exists, NASM will overwrite it, unless it has the same name as the input file, in which case it will give a warning and use nasm.out as the output file name instead.

For situations in which this behaviour is unacceptable, NASM provides the -o command-line option, which allows you to specify your desired output file name. You invoke -o by following it with the name you wish for the output file, either with or without an intervening space. For example:

nasm -f bin program.asm -o program.com 
nasm -f bin driver.asm -odriver.sys

Note that this is a small o, and is different from a capital O , which is used to specify the number of optimisation passes required. See NASM Command Line O.

NASM Command-Line -p
(Pre-Include File)

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

NASM allows you to specify files to be pre-included into your source file, by the use of the -p option. So running

nasm myfile.asm -p myinc.inc

is equivalent to running nasm myfile.asm and placing the directive %include "myinc.inc" at the start of the file.

For consistency with the -I, -D and -U options, this option can also be specified as -P.

NASM Command-Line -s
(Send Errors To stdout)

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

The -s option redirects error messages to stdout rather than stderr, so it can be redirected under MS-DOS. To assemble the file myfile.asm and pipe its output to the more program, you can type:

nasm -s -f obj myfile.asm   more

See also the -E option, NASM Command Line E.

NASM Command-Line --prefix and --postfix
(Prefix/Postfix Underscore To Variable Names)

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

The --prefix and --postfix options prepend or append (respectively) the given argument to all global or extern variables. E.g. --prefix_ prepends an underscore to all global and external variables, as required by C/C++ (sometimes, but not always).

NASM Command-Line -t
(TASM Compatibility Mode)

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

NASM includes a limited form of compatibility with Borland's TASM. When NASM's -t option is used, the following changes are made:

local labels may be prefixed with @@ instead of .
TASM-style response files beginning with @ may be specified on the command line. This is different from the -@resp style that NASM natively supports.
size override is supported within brackets. In TASM compatible mode, a size override inside square brackets changes the size of the operand, and not the address type of the operand as it does in NASM syntax. E.g. mov eax,[DWORD val] is valid syntax in TASM compatibility mode. Note that you lose the ability to override the default address type for the instruction.
%arg preprocessor directive is supported which is similar to TASM's ARG directive.
%local preprocessor directive
%stacksize preprocessor directive
unprefixed forms of some directives supported (arg, elif, else, endif, if, ifdef, ifdifi, ifndef, include, local)
more...

For more information on the directives, see the section on TASM Compatiblity preprocessor directives in section 4.9.

NASM Command-Line -u
(Undefine A Macro)

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

The -u option undefines a macro that would otherwise have been pre-defined, either automatically or by a -p or -d option specified earlier on the command lines.

For example, the following command line:

nasm myfile.asm -dFOO=100 -uFOO

would result in FOO not being a predefined macro in the program. This is useful to override options specified at a different point in a Makefile.

For Makefile compatibility with many C compilers, this option can also be specified as -U.

NASM Command-Line -v
(Display Version)

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

Typing NASM -v will display the version of NASM which you are using, and the date on which it was compiled. This replaces the deprecated -r.

You will need the version number if you report a bug.

NASM Command-Line -w
(Enable/Disable Warnings)

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

NASM can observe many conditions during the course of assembly which are worth mentioning to the user, but not a sufficiently severe error to justify NASM refusing to generate an output file. These conditions are reported like errors, but come up with the word 'warning' before the message. Warnings do not prevent NASM from generating an output file and returning a success status to the operating system.

Some conditions are even less severe than that: they are only sometimes worth mentioning to the user. Therefore NASM supports the -w command-line option, which enables or disables certain classes of assembly warning. Such warning classes are described by a name, for example orphan-labels; you can enable warnings of this class by the command-line option -w+orphan-labels and disable it by -w-orphan-labels.

The suppressible warning classes are:

macro-params covers warnings about multi-line macros being invoked with the wrong number of parameters. This warning class is enabled by default; see section 4.3.1 for an example of why you might want to disable it.
macro-selfref warns if a macro references itself. This warning class is enabled by default.
orphan-labels covers warnings about source lines which contain no instruction but define a label without a trailing colon. NASM does not warn about this somewhat obscure condition by default; see Encoding With NASM for an example of why you might want it to.
number-overflow covers warnings about numeric constants which don't fit in 32 bits (for example, it's easy to type one too many Fs and produce 0x7ffffffff by mistake). This warning class is enabled by default.
gnu-elf-extensions warns if 8-bit or 16-bit relocations are used in -f elf format. The GNU extensions allow this. This warning class is enabled by default.
In addition, warning classes may be enabled or disabled across sections of source code with [warning +warning-name] or [warning -warning-name]. No "user form" (without the brackets) exists.

NASM Command-Line -X
(Select Error Reporting Format)

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

This option can be used to select an error reporting format for any error messages that might be produced by NASM.

Currently, two error reporting formats may be selected. They are the -Xvc option and the -Xgnu option. The GNU format is the default and looks like this:

filename.asm:65: error: specific error message

where filename.asm is the name of the source file in which the error was detected, 65 is the source file line number on which the error was detected, error is the severity of the error (this could be warning), and specific error message is a more detailed text message which should help pinpoint the exact problem.

The other format, specified by -Xvc is the style used by Microsoft Visual C++ and some other programs. It looks like this:

filename.asm(65) : error: specific error message

where the only difference is that the line number is in parentheses instead of being delimited by colons.

See also the Visual C++ output format, section 6.3.

NASM Command-Line -y
(Display Debug Formats)

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

Typing nasm -f <option> -y will display a list of the available debug info formats for the given output format. The default format is indicated by an asterisk. E.g. nasm -f obj -y yields * borland. (as of 0.98.35, the only debug info format implemented).

The NASMENV Environment Variable

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y

If you define an environment variable called NASMENV, the program will interpret it as a list of extra command-line options, which are processed before the real command line. You can use this to define standard search directories for include files, by putting -i options in the NASMENV variable.

The value of the variable is split up at white space, so that the value -s -ic:\nasmlib will be treated as two separate options. However, that means that the value -dNAME="my name" won't do what you might want, because it will be split at the space and the NASM command-line processing will get confused by the two nonsensical words -dNAME="my and name".

To get round this, NASM provides a feature whereby, if you begin the NASMENV environment variable with some character that isn't a minus sign, then NASM will treat this character as the separator character for options. So setting the NASMENV variable to the value !-s!-ic:\nasmlib is equivalent to setting it to -s -ic:\nasmlib, but !-dNAME="my name" will work.

This environment variable was previously called NASM. This was changed with version 0.98.31.

Quick Start for MASM Users

-a -d -E -e -F -f -g -h -hf -i -l -M

-O -o -p -s -t -u -v -w -X -y