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<code><nobr>MS-DOS</nobr></code>. To assemble the file
<code><nobr>myfile.asm</nobr></code> and pipe its output to the
<code><nobr>more</nobr></code> program, you can type:
<p><pre>
nasm -s -f obj myfile.asm | more
</pre>
<p>See also the <code><nobr>-E</nobr></code> option,
<a href="#section-2.1.8">section 2.1.8</a>.
<h4><a name="section-2.1.10">2.1.10 The <code><nobr>-i</nobr></code> Option: Include File Search Directories</a></h4>
<p>When NASM sees the <code><nobr>%include</nobr></code> or
<code><nobr>incbin</nobr></code> directive in a source file (see
<a href="nasmdoc4.html#section-4.6">section 4.6</a> or
<a href="nasmdoc3.html#section-3.2.3">section 3.2.3</a>), 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
<code><nobr>-i</nobr></code> option. Therefore you can include files from a
macro library, for example, by typing
<p><pre>
nasm -ic:\macrolib\ -f obj myfile.asm
</pre>
<p>(As usual, a space between <code><nobr>-i</nobr></code> and the path
name is allowed, and optional).
<p>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 <code><nobr>-i</nobr></code>
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.
<p>(You can use this to your advantage, if you're really perverse, by
noting that the option <code><nobr>-ifoo</nobr></code> will cause
<code><nobr>%include "bar.i"</nobr></code> to search for the file
<code><nobr>foobar.i</nobr></code>...)
<p>If you want to define a <em>standard</em> include search path, similar
to <code><nobr>/usr/include</nobr></code> on Unix systems, you should place
one or more <code><nobr>-i</nobr></code> directives in the
<code><nobr>NASMENV</nobr></code> environment variable (see
<a href="#section-2.1.22">section 2.1.22</a>).
<p>For Makefile compatibility with many C compilers, this option can also
be specified as <code><nobr>-I</nobr></code>.
<h4><a name="section-2.1.11">2.1.11 The <code><nobr>-p</nobr></code> Option: Pre-Include a File</a></h4>
<p>NASM allows you to specify files to be <em>pre-included</em> into your
source file, by the use of the <code><nobr>-p</nobr></code> option. So
running
<p><pre>
nasm myfile.asm -p myinc.inc
</pre>
<p>is equivalent to running <code><nobr>nasm myfile.asm</nobr></code> and
placing the directive <code><nobr>%include "myinc.inc"</nobr></code> at the
start of the file.
<p>For consistency with the <code><nobr>-I</nobr></code>,
<code><nobr>-D</nobr></code> and <code><nobr>-U</nobr></code> options, this
option can also be specified as <code><nobr>-P</nobr></code>.
<h4><a name="section-2.1.12">2.1.12 The <code><nobr>-d</nobr></code> Option: Pre-Define a Macro</a></h4>
<p>Just as the <code><nobr>-p</nobr></code> option gives an alternative to
placing <code><nobr>%include</nobr></code> directives at the start of a
source file, the <code><nobr>-d</nobr></code> option gives an alternative
to placing a <code><nobr>%define</nobr></code> directive. You could code
<p><pre>
nasm myfile.asm -dFOO=100
</pre>
<p>as an alternative to placing the directive
<p><pre>
%define FOO 100
</pre>
<p>at the start of the file. You can miss off the macro value, as well: the
option <code><nobr>-dFOO</nobr></code> is equivalent to coding
<code><nobr>%define FOO</nobr></code>. This form of the directive may be
useful for selecting assembly-time options which are then tested using
<code><nobr>%ifdef</nobr></code>, for example
<code><nobr>-dDEBUG</nobr></code>.
<p>For Makefile compatibility with many C compilers, this option can also
be specified as <code><nobr>-D</nobr></code>.
<h4><a name="section-2.1.13">2.1.13 The <code><nobr>-u</nobr></code> Option: Undefine a Macro</a></h4>
<p>The <code><nobr>-u</nobr></code> option undefines a macro that would
otherwise have been pre-defined, either automatically or by a
<code><nobr>-p</nobr></code> or <code><nobr>-d</nobr></code> option
specified earlier on the command lines.
<p>For example, the following command line:
<p><pre>
nasm myfile.asm -dFOO=100 -uFOO
</pre>
<p>would result in <code><nobr>FOO</nobr></code> <em>not</em> being a
predefined macro in the program. This is useful to override options
specified at a different point in a Makefile.
<p>For Makefile compatibility with many C compilers, this option can also
be specified as <code><nobr>-U</nobr></code>.
<h4><a name="section-2.1.14">2.1.14 The <code><nobr>-e</nobr></code> Option: Preprocess Only</a></h4>
<p>NASM allows the preprocessor to be run on its own, up to a point. Using
the <code><nobr>-e</nobr></code> 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
<code><nobr>-o</nobr></code> option is also used).
<p>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
<p><pre>
%assign tablesize ($-tablestart)
</pre>
<p>will cause an error in preprocess-only mode.
<h4><a name="section-2.1.15">2.1.15 The <code><nobr>-a</nobr></code> Option: Don't Preprocess At All</a></h4>
<p>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
<code><nobr>-a</nobr></code> option, requiring no argument, instructs NASM
to replace its powerful preprocessor with a stub preprocessor which does
nothing.
<h4><a name="section-2.1.16">2.1.16 The <code><nobr>-On</nobr></code> Option: Specifying Multipass Optimization.</a></h4>
<p>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.
<p>Using the <code><nobr>-O</nobr></code> option, you can tell NASM to
carry out multiple passes. The syntax is:
<ul>
<li><code><nobr>-O0</nobr></code> 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.
<li><code><nobr>-O1</nobr></code> 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.
<li><code><nobr>-On</nobr></code> multi-pass optimization, minimize branch
offsets; also will minimize signed immediate bytes, overriding size
specification unless the <code><nobr>strict</nobr></code> keyword has been
used (see <a href="nasmdoc3.html#section-3.7">section 3.7</a>). The number
specifies the maximum number of passes. The more passes, the better the
code, but the slower is the assembly.
</ul>
<p>Note that this is a capital O, and is different from a small o, which is
used to specify the output format. See <a href="#section-2.1.1">section
2.1.1</a>.
<h4><a name="section-2.1.17">2.1.17 The <code><nobr>-t</nobr></code> option: Enable TASM Compatibility Mode</a></h4>
<p>NASM includes a limited form of compatibility with Borland's
<code><nobr>TASM</nobr></code>. When NASM's <code><nobr>-t</nobr></code>
option is used, the following changes are made:
<ul>
<li>local labels may be prefixed with <code><nobr>@@</nobr></code> instead
of <code><nobr>.</nobr></code>
<li>TASM-style response files beginning with <code><nobr>@</nobr></code>
may be specified on the command line. This is different from the
<code><nobr>-@resp</nobr></code> style that NASM natively supports.
<li>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.
<code><nobr>mov eax,[DWORD val]</nobr></code> is valid syntax in TASM
compatibility mode. Note that you lose the ability to override the default
address type for the instruction.
<li><code><nobr>%arg</nobr></code> preprocessor directive is supported
which is similar to TASM's <code><nobr>ARG</nobr></code> directive.
<li><code><nobr>%local</nobr></code> preprocessor directive
<li><code><nobr>%stacksize</nobr></code> preprocessor directive
<li>unprefixed forms of some directives supported
(<code><nobr>arg</nobr></code>, <code><nobr>elif</nobr></code>,
<code><nobr>else</nobr></code>, <code><nobr>endif</nobr></code>,
<code><nobr>if</nobr></code>, <code><nobr>ifdef</nobr></code>,
<code><nobr>ifdifi</nobr></code>, <code><nobr>ifndef</nobr></code>,
<code><nobr>include</nobr></code>, <code><nobr>local</nobr></code>)
<li>more...
</ul>
<p>For more information on the directives, see the section on TASM
Compatiblity preprocessor directives in
<a href="nasmdoc4.html#section-4.9">section 4.9</a>.
<h4><a name="section-2.1.18">2.1.18 The <code><nobr>-w</nobr></code> Option: Enable or Disable Assembly Warnings</a></h4>
<p>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.
<p>Some conditions are even less severe than that: they are only sometimes
worth mentioning to the user. Therefore NASM supports the
<code><nobr>-w</nobr></code> command-line option, which enables or disables
certain classes of assembly warning. Such warning classes are described by
a name, for example <code><nobr>orphan-labels</nobr></code>; you can enable
warnings of this class by the command-line option
<code><nobr>-w+orphan-labels</nobr></code> and disable it by
<code><nobr>-w-orphan-labels</nobr></code>.
<p>The suppressible warning classes are:
<ul>
<li><code><nobr>macro-params</nobr></code> covers warnings about multi-line
macros being invoked with the wrong number of parameters. This warning
class is enabled by default; see
<a href="nasmdoc4.html#section-4.3.1">section 4.3.1</a> for an example of
why you might want to disable it.
<li><code><nobr>macro-selfref</nobr></code> warns if a macro references
itself. This warning class is enabled by default.
<li><code><nobr>orphan-labels</nobr></code> 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 <a href="nasmdoc3.html#section-3.1">section 3.1</a> for an example of