make.html

unix 下的C开发手册,还用详细的例程。

has ensured that all of the prerequisites of a target are
up-to-date and if the target is out-of-date, the commands
associated with the target entry are executed.
If there are
no commands listed for the target, the target is treated
as up-to-date.
<h5><a name = "tag_001_014_1377_001">&nbsp;</a>Makefile Syntax</h5>
A makefile can contain rules, macro definitions (see
<xref href=mkmacro><a href="#tag_001_014_1377_004">
Macros
</a></xref>),
and comments.
There are two kinds of rules:
inference rules
and target rules.
The
<i>make</i>
utility contains a set of built-in inference rules.
If the
<b>-r</b>
option is present, the built-in rules are not used and the suffix
list is cleared.
Additional rules of both types can be specified in a makefile.
If a rule or macro is defined more than once, the value
of the rule or macro will be that of the last one specified.
Comments start with a number sign
(#)
and continue until an unescaped
newline character
is reached.
<p>
By default, the following files are tried in sequence:
<b>./makefile</b>,
<b>./Makefile</b>,
<b>./s.makefile</b>,
<b>SCCS/s.makefile</b>,
<b>./s.Makefile</b>,
and
<b>SCCS/s.Makefile</b>.
<p>
The
<b>-f</b>
option directs
<i>make</i>
to ignore any of these default files
and use the specified argument as a makefile instead.
If the "-" argument is specified, standard input will be used.
<p>
The term
<i>makefile</i>
is used to refer to any rules provided by the
user, whether in
<b>./makefile</b>
or its variants,
or specified by the
<b>-f</b>
option.
<p>
The rules in makefiles consist of the following types of lines:
target rules, including special targets (see
<xref href=mktarg><a href="#tag_001_014_1377_003">
Target Rules
</a></xref>);
inference rules (see
<xref href=infrules><a href="#tag_001_014_1377_005">
Inference Rules
</a></xref>);
macro definitions (see
<xref href=mkmacro><a href="#tag_001_014_1377_004">
Macros
</a></xref>);
empty lines;
and comments.
Comments start with a number sign
(#)
and continue until an unescaped
newline character
is reached.
<p>
When an escaped
newline character
(one preceded by a
<b>backslash</b>)
is found anywhere in the makefile, it is replaced,
along with any leading white space on the following line, with a single
space character.
<h5><a name = "tag_001_014_1377_002">&nbsp;</a>Makefile Execution</h5>
Command lines are processed one at a time
by writing the command line to the standard output (unless
one of the conditions listed below under "@"
suppresses the writing)
and executing the commands in the line.
A tab character may precede the command to standard output.
Commands will be executed
by passing the command line to the command interpreter in
the same manner as if the string were the argument to
the <b>XSH</b> specification
<i><a href="../xsh/system.html">system()</a></i>
function.
<p>
The environment for the command being executed will
contain all of the variables in the environment of
<i>make</i>.
The macros from the command line to
<i>make</i>
will be added to
<i>make</i>'s
environment.
Other implementation-dependent
variables may also be added to
<i>make</i>'s
environment.
If any command-line macro has been defined elsewhere, the
command-line value will overwrite the existing value.
If the
<i>MAKEFLAGS</i>
variable is not set in the environment in which
<i>make</i>
was invoked, in the makefile or on the
command line, it will be created by
<i>make</i>,
and will contain all options specified on the command line except for the
<b>-f</b>
and
<b>-p</b>
options.
It may also contain implementation-dependent options.
<p>
By default, when
<i>make</i>
receives a non-zero status from the
execution of a command, it terminates with an error message
to standard error.
<p>
Command lines can have one or more of the following prefixes:
a hyphen
(-),
an at sign
(@),
or a plus sign
(+).
These modify the way in which
<i>make</i>
processes the command.
When a command is written to standard output,
the prefix is not included in the output.
<dl compact>

<dt><b>-</b><dd>If the command prefix contains a hyphen,
or the
<b>-i</b>
option is present, or the special target
<b>.IGNORE</b>
has either the current target as a prerequisite or has no prerequisites,
any error found while executing the command will be ignored.

<dt>@<dd>If the command prefix contains an at sign
and the command-line
<b>-n</b>
option is not specified, or the
<b>-s</b>
option
is present, or the special target
<b>.SILENT</b>
has either the current target as a prerequisite or has no prerequisites,
the command will not be written to standard output before it is executed.

<dt><b>+</b><dd>If the command prefix contains a plus sign,
this indicates a command line that will be executed even if
<b>-n</b>,
<b>-q</b>
or
<b>-t</b>
is specified.

</dl>
<h5><a name = "tag_001_014_1377_003">&nbsp;</a>Target Rules</h5>
<xref type="5" name="mktarg"></xref>
Target rules are formatted as follows:
<pre>
<code>
<i>target </i><b>[</b><i>target</i>...<b>]</b>:&nbsp;<b>[</b><i>prerequisite</i>...<b>][;</b><i>command</i><b>]
[</b>&lt;tab&gt;<i>command</i><b>]</b>
&lt;tab&gt;command
...<b>]</b>

<i>line that does not begin with </i>&lt;tab&gt;
</code>
</pre>
<p>
Target entries are specified by a
blank-character-separated,
non-null list of targets, then a colon, then a
blank-character-separated,
possibly empty list of prerequisites.
Text following a semicolon,
if any, and all following lines that begin with a
tab character,
are command lines to be executed to update the target.
The first non-empty line that does not begin with a
tab character
or
"#"
begins a new entry.
An empty or blank line, or a line beginning with
"#",
may begin a new entry.
<p>
Applications must select target names from the
set of characters consisting solely of periods,
underscores, digits and alphabetics
from the portable character set (see
the <b>XBD</b> specification, <a href="../xbd/charset.html#tag_001_001"><b>Portable Character Set</b>&nbsp;</a> ).
Implementations may allow other characters
in target names as extensions.
The interpretation of targets containing the characters "%" and """
is implementation-dependent.
<p>
A target that has prerequisites, but does not have any commands,
can be used to add to the prerequisite list for that target.
Only one target rule for any given target can contain commands.
<p>
Lines that begin with one of the following are called
<i>special targets</i>
and control the operation of
<i>make</i>:
<dl compact>

<dt>.DEFAULT<dd>If the makefile uses this special target,
it must be specified with commands, but
without prerequisites.
The commands will be used by
<i>make</i>
if there are no other rules
available to build a target.

<dt>.IGNORE<dd>Prerequisites of this special target are targets themselves;
this will cause errors from commands associated with them
to be ignored in the same manner as specified by the
<b>-i</b>
option.
Subsequent occurrences of
<b>.IGNORE</b>
add to the list of targets ignoring command errors.
If no prerequisites are specified,
<i>make</i>
will behave as if the
<b>-i</b>
option had been specified and errors
from all commands associated with all targets will be ignored.

<dt>.POSIX<dd>This special target must be specified without prerequisites or commands.
If it appears before the first non-comment line in the makefile,
<i>make</i>
will process the makefile as specified by this section;
otherwise, the behaviour of
<i>make</i>
is unspecified.

<dt>.PRECIOUS<dd>Prerequisites of this special target will not be removed if
<i>make</i>
receives one of the asynchronous events explicitly described in
the ASYNCHRONOUS EVENTS section.
Subsequent occurrences of
<b>.PRECIOUS</b>
add to the list of precious files.
If no prerequisites are specified,
all targets in the makefile will be treated as if specified with
<b>.PRECIOUS</b>.

<dt>.SCCS_GET<dd>This special target must be specified without prerequisites.
If this special target is included in a
makefile, the commands specified with this target
replace the default commands associated with this
special target.
(See
<xref href=mkdefr><a href="#tag_001_014_1377_008">
Default Rules
</a></xref>.)
The commands specified with this target are used to get all
SCCS files that are not found in the current directory.

When source files are named in a dependency list,
<i>make</i>
treats them just like any other target.
Because the
source file is presumed to be present in the directory,
there is no need to add an entry for it to the makefile.
When a target has no dependencies, but is present in the
directory,
<i>make</i>
assumes that that file is up-to-date.
If, however, an SCCS file named
<b>SCCS/s.</b><i>source_file</i>
is found for a target
<i>source_file</i>,
<i>make</i>
does some additional checking to assure that the target is up-to-date.
If the target is missing, or if the SCCS file is newer,
<i>make</i>
automatically issues the commands specified
for the
<b>.SCCS_GET</b>
special target to retrieve the most
recent version.
However, if the target is writable by
anyone,
<i>make</i>
does not retrieve a new version.

<dt>.SILENT<dd>Prerequisites of this special target are targets themselves;
this causes commands associated with them to not be written
to the standard output before they are executed.
Subsequent occurrences of
<b>.SILENT</b>
add to the list of targets with silent commands.
If no prerequisites are specified,
<i>make</i>
will behave as if the
<b>-s</b>
option had been specified and no commands or touch messages associated with
any target will be written to standard output.

<dt>.SUFFIXES<dd>Prerequisites of
<b>.SUFFIXES</b>
are appended to the list
of known suffixes and are used
in conjunction with the inference rules (see
<xref href=infrules><a href="#tag_001_014_1377_005">
Inference Rules
</a></xref>).
If
<b>.SUFFIXES</b>
does not have
any prerequisites, the list of known suffixes will be cleared.
Makefiles must not associate commands with
<b>.SUFFIXES</b>.

</dl>
<p>
Targets with names consisting of a leading period followed by
the upper-case letters
<b>POSIX</b>
and then any other characters are reserved for future standardisation.
Targets with names consisting of a leading period followed by
one or more upper-case letters are reserved for implementation extensions.
<h5><a name = "tag_001_014_1377_004">&nbsp;</a>Macros</h5>
<xref type="5" name="mkmacro"></xref>
Macro definitions are in the form:
<p>
<dl compact><dt> <dd>
<i>string1</i>
"="
<b>[</b><i>string2</i><b>]</b>
</dl>
</p>
<p>
The macro named
<i>string1</i>
is defined as having the value of
<i>string2</i>,
where
<i>string2</i>
is defined as all characters,
if any, after the equal sign,
up to a comment character
(#)
or an unescaped
newline
character.
Any
blank characters
immediately before or after the equal sign
will be ignored.
<p>
Subsequent appearances of
<b>$(</b><i>string1</i><b>)</b>
or
<b>${</b><i>string1</i><b>}</b>
are replaced by
<i>string2</i>.
The parentheses or braces are optional if
<i>string1</i>
is a single character.
The macro
$$
is replaced by the single character "$".
<p>
Applications must select macro names from the
set of characters consisting solely of periods,
underscores, digits and alphabetics
from the portable character set (see
the <b>XBD</b> specification, <a href="../xbd/charset.html#tag_001_001"><b>Portable Character Set</b>&nbsp;</a> ).
A macro name cannot contain an equal sign.
Implementations may allow other characters
in macro names as extensions.
<p>
Macros can appear anywhere in the makefile.
Macros in target lines will be evaluated when the target line is read.
Macros in command lines will be evaluated when the command is executed.
Macros in macro definition lines will not be evaluated
until the new macro being defined is used in a rule or command.
A macro that has not been defined will evaluate to a null string
without causing any error condition.
<p>
The forms
<b>$(</b><i>string1</i><b>[:</b><i>subst1</i><b>=[</b><i>subst2</i><b>]])</b>
or
<b>${</b><i>string1</i><b>[:</b><i>subst1</i><b>=[</b><i>subst2</i><b>]]}</b>
can be used to replace
all occurrences of
<i>subst1</i>
with
<i>subst2</i>
when the macro substitution is performed.
The
<i>subst1</i>
to be replaced is recognised when it is a suffix
at the end of a word in
<i>string1</i>
(where a
<i>word</i>,
in this context, is defined to be a string
delimited by the beginning of the line, a
blank or newline character).
<p>
Macro assignments will be accepted from the sources listed below,
in the order shown.
If a macro name
already exists at the time it is being processed, the newer definition
will replace the existing definition.
<ol>
<p>
<li>
Macros defined in
<i>make</i>'s
built-in inference rules.
<p>
<li>
The contents of the environment,
including the variables with null values,
in the order defined in the environment.
<p>
<li>
Macros defined in the makefiles,
processed in the order specified.
<p>
<li>
Macros specified on the command line.
It is unspecified whether the internal macros defined in
<xref href=mkimacs><a href="#tag_001_014_1377_007">
Internal Macros
</a></xref>
are accepted from the command line.
<p>
</ol>
<p>
If the
<b>-e</b>
option is specified, the order of processing sources items 2 and 3
will be reversed.
<p>
The