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早期freebsd实现

Variable assignment.
.RE
.IP "\&"
Of these all, the
.CW m
and
.CW s
letters will be most useful to you.
If the
.B \-d
is the final argument or the argument from which it would get these
key letters (see below for a note about which argument would be used)
begins with a
.B \- ,
all of these debugging flags will be set, resulting in massive amounts
of output.
.IP "\fB\-f\fP \fImakefile\fP"
.Ix 0 def flags -f
Specify a makefile to read different from the standard makefiles
.CW Makefile "\&" (
or
.CW makefile ).
.Ix 0 ref makefile default
.Ix 0 ref makefile other
If
.I makefile
is ``\-'', PMake uses the standard input. This is useful for making
quick and dirty makefiles.\|.\|.
.Ix 0 ref makefile "quick and dirty"
.IP \fB\-h\fP
.Ix 0 def flags -h
Prints out a summary of the various flags PMake accepts. It can also
be used to find out what level of concurrency was compiled into the
version of PMake you are using (look at
.B \-J
and
.B \-L )
and various other information on how PMake was configured.
.Ix 0 ref configuration
.Ix 0 ref makefile system
.IP \fB\-i\fP
.Ix 0 def flags -i
If you give this flag, PMake will ignore non-zero status returned
by any of its shells. It's like placing a `\-' before all the commands
in the makefile.
.IP \fB\-k\fP
.Ix 0 def flags -k
This is similar to
.B \-i
in that it allows PMake to continue when it sees an error, but unlike
.B \-i ,
where PMake continues blithely as if nothing went wrong,
.B \-k
causes it to recognize the error and only continue work on those
things that don't depend on the target, either directly or indirectly (through
depending on something that depends on it), whose creation returned the error.
The `k' is for ``keep going''.\|.\|.
.Ix 0 ref target
.IP \fB\-l\fP
.Ix 0 def flags -l
PMake has the ability to lock a directory against other
people executing it in the same directory (by means of a file called
``LOCK.make'' that it creates and checks for in the directory). This
is a Good Thing because two people doing the same thing in the same place
can be disastrous for the final product (too many cooks and all that).
Whether this locking is the default is up to your system
administrator. If locking is on,
.B \-l
will turn it off, and vice versa. Note that this locking will not
prevent \fIyou\fP from invoking PMake twice in the same place \*- if
you own the lock file, PMake will warn you about it but continue to execute.
.IP \fB\-n\fP
.Ix 0 def flags -n
This flag tells PMake not to execute the commands needed to update the
out-of-date targets in the makefile. Rather, PMake will simply print
the commands it would have executed and exit. This is particularly
useful for checking the correctness of a makefile. If PMake doesn't do
what you expect it to, it's a good chance the makefile is wrong.
.IP "\fB\-p\fP \fInumber\fP"
.Ix 0 def flags -p
.Ix 0 ref debugging
This causes PMake to print its input in a reasonable form, though
not necessarily one that would make immediate sense to anyone but me. The
.I number
is a bitwise-or of 1 and 2 where 1 means it should print the input
before doing any processing and 2 says it should print it after
everything has been re-created. Thus
.CW "\-p 3"
would print it twice\*-once before processing and once after (you
might find the difference between the two interesting). This is mostly
useful to me, but you may find it informative in some bizarre circumstances.
.IP \fB\-q\fP
.Ix 0 def flags -q
If you give PMake this flag, it will not try to re-create anything. It
will just see if anything is out-of-date and exit non-zero if so.
.IP \fB\-r\fP
.Ix 0 def flags -r
When PMake starts up, it reads a default makefile that tells it what
sort of system it's on and gives it some idea of what to do if you
don't tell it anything. I'll tell you about it in chapter 3. If you
give this flag, PMake won't read the default makefile.
.IP \fB\-s\fP
.Ix 0 def flags -s
This causes PMake to not print commands before they're executed. It
is the equivalent of putting an `@' before every command in the
makefile.
.IP \fB\-t\fP
.Ix 0 def flags -t
Rather than try to re-create a target, PMake will simply ``touch'' it
so as to make it appear up-to-date. If the target didn't exist before,
it will when PMake finishes, but if the target did exist, it will
appear to have been updated.
.IP \fB\-v\fP
.Ix 0 def flags -v
This is a mixed-compatibility flag intended to mimic the System V
version of Make. It is the same as giving
.B \-B ,
and
.B \-V
as well as turning off directory locking. Targets can still be created
in parallel, however. This is the mode PMake will enter if it is
invoked either as
.CW smake '' ``
or
.CW vmake ''. ``
.IP \fB\-x\fP
.Ix 0 def flags -x
This tells PMake it's ok to export jobs to other machines, if they're
available. It is used when running in Make mode, as exporting in this
mode tends to make things run slower than if the commands were just
executed locally.
.IP \fB\-B\fP
.Ix 0 ref compatibility
.Ix 0 def flags -B
Forces PMake to be as backwards-compatible with Make as possible while
still being itself.
This includes:
.RS
.IP \(bu 2
Executing one shell per shell command
.IP \(bu 2
Expanding anything that looks even vaguely like a variable, with the
empty string replacing any variable PMake doesn't know.
.IP \(bu 2
Refusing to allow you to escape a `#' with a backslash.
.IP \(bu 2
Permitting undefined variables on dependency lines and conditionals
(see below). Normally this causes PMake to abort.
.RE
.IP \fB\-C\fP
.Ix 0 def flags -C
This nullifies any and all compatibility mode flags you may have given
or implied up to the time the
.B \-C
is encountered. It is useful mostly in a makefile that you wrote for PMake
to avoid bad things happening when someone runs PMake as
.CW make '' ``
or has things set in the environment that tell it to be compatible.
.B \-C
is
.I not
placed in the
.CW PMAKE
environment variable or the
.CW .MAKEFLAGS
or
.CW MFLAGS
global variables.
.Ix 0 ref variable environment PMAKE
.Ix 0 ref variable global .MAKEFLAGS
.Ix 0 ref variable global MFLAGS
.Ix 0 ref .MAKEFLAGS variable
.Ix 0 ref MFLAGS
.IP "\fB\-D\fP \fIvariable\fP"
.Ix 0 def flags -D
Allows you to define a variable to have 
.CW 1 '' ``
as its value.  The variable is a global variable, not a command-line
variable. This is useful mostly for people who are used to the C
compiler arguments and those using conditionals, which I'll get into
in section 4.3
.Rm 1 4.3
.IP "\fB\-I\fP \fIdirectory\fP"
.Ix 0 def flags -I
Tells PMake another place to search for included makefiles. Yet
another thing to be explained in chapter 3 (section 3.2, to be
precise).
.Rm 2 3.2
.IP "\fB\-J\fP \fInumber\fP"
.Ix 0 def flags -J
Gives the absolute maximum number of targets to create at once on both
local and remote machines.
.IP "\fB\-L\fP \fInumber\fP"
.Ix 0 def flags -L
This specifies the maximum number of targets to create on the local
machine at once. This may be 0, though you should be wary of doing
this, as PMake may hang until a remote machine becomes available, if
one is not available when it is started.
.IP \fB\-M\fP
.Ix 0 ref compatibility
.Ix 0 def flags -M
This is the flag that provides absolute, complete, full compatibility
with Make. It still allows you to use all but a few of the features of
PMake, but it is non-parallel. This is the mode PMake enters if you
call it
.CW make .'' ``
.IP \fB\-P\fP
.Ix 0 def flags -P
.Ix 0 ref "output control"
When creating targets in parallel, several shells are executing at
once, each wanting to write its own two cent's-worth to the screen.
This output must be captured by PMake in some way in order to prevent
the screen from being filled with garbage even more indecipherable
than you usually see. PMake has two ways of doing this, one of which
provides for much cleaner output and a clear separation between the
output of different jobs, the other of which provides a more immediate
response so one can tell what is really happpening. The former is done
by notifying you when the creation of a target starts, capturing the
output and transferring it to the screen all at once when the job
finishes. The latter is done by catching the output of the shell (and
its children) and buffering it until an entire line is received, then
printing that line preceded by an indication of which job produced
the output. Since I prefer this second method, it is the one used by
default. The first method will be used if you give the
.B \-P
flag to PMake.
.IP \fB\-V\fP
.Ix 0 def flags -V
As mentioned before, the
.B \-V
flag tells PMake to use Make's style of expanding variables,
substituting the empty string for any variable it doesn't know.
.IP \fB\-W\fP
.Ix 0 def flags -W
There are several times when PMake will print a message at you that is
only a warning, i.e. it can continue to work in spite of your having
done something silly (such as forgotten a leading tab for a shell
command). Sometimes you are well aware of silly things you have done
and would like PMake to stop bothering you. This flag tells it to shut
up about anything non-fatal.
.IP \fB\-X\fP
.Ix 0 def flags -X
This flag causes PMake to not attempt to export any jobs to another
machine.
.LP
Several flags may follow a single `\-'. Those flags that require
arguments take them from successive parameters. E.g.
.DS
pmake -fDnI server.mk DEBUG /chip2/X/server/include
.DE
will cause PMake to read
.CW server.mk
as the input makefile, define the variable
.CW DEBUG
as a global variable and look for included makefiles in the directory
.CW /chip2/X/server/include .
.xH 2 Summary
.LP
A makefile is made of four types of lines:
.RS
.IP \(bu 2
Dependency lines
.IP \(bu 2
Creation commands
.IP \(bu 2
Variable assignments
.IP \(bu 2
Comments, include statements and conditional directives
.RE
.LP
A dependency line is a list of one or more targets, an operator
.CW : ', (`
.CW :: ', `
or
.CW ! '), `
and a list of zero or more sources. Sources may contain wildcards and
certain local variables.
.LP
A creation command is a regular shell command preceded by a tab. In
addition, if the first two characters after the tab (and other
whitespace) are a combination of
.CW @ ' `
or
.CW - ', `
PMake will cause the command to not be printed (if the character is
.CW @ ') `
or errors from it to be ignored (if
.CW - '). `
A blank line, dependency line or variable assignment terminates a
creation script. There may be only one creation script for each target
with a
.CW : ' `
or
.CW ! ' `
operator.
.LP
Variables are places to store text. They may be unconditionally
assigned-to using the
.CW = ' `
.Ix 0 ref =
.Ix 0 ref variable assignment
operator, appended-to using the
.CW += ' `
.Ix 0 ref +=
.Ix 0 ref variable assignment appended
operator, conditionally (if the variable is undefined) assigned-to
with the
.CW ?= ' `
.Ix 0 ref ?=
.Ix 0 ref variable assignment conditional
operator, and assigned-to with variable expansion with the
.CW := ' `
.Ix 0 ref :=
.Ix 0 ref variable assignment expanded
operator. The output of a shell command may be assigned to a variable
using the
.CW != ' `
.Ix 0 ref !=
.Ix 0 ref variable assignment shell-output
operator.  Variables may be expanded (their value inserted) by enclosing
their name in parentheses or curly braces, prceeded by a dollar sign.
A dollar sign may be escaped with another dollar sign. Variables are
not expanded if PMake doesn't know about them. There are seven local
variables:
.CW .TARGET ,
.CW .ALLSRC ,
.CW .OODATE ,
.CW .PREFIX ,
.CW .IMPSRC ,
.CW .ARCHIVE ,
and
.CW .MEMBER .
Four of them
.CW .TARGET , (
.CW .PREFIX ,
.CW .ARCHIVE ,
and
.CW .MEMBER )
may be used to specify ``dynamic sources.''
.Ix 0 ref "dynamic source"
.Ix 0 ref source dynamic
Variables are good. Know them. Love them. Live them.
.LP
Debugging of makefiles is best accomplished using the
.B \-n ,
.B "\-d m" ,
and
.B "\-p 2"
flags.
.xH 2 Exercises
.ce
\s+4\fBTBA\fP\s0
.xH 1 Short-cuts and Other Nice Things
.LP
Based on what I've told you so far, you may have gotten the impression
that PMake is just a way of storing away commands and making sure you
don't forget to compile something. Good. That's just what it is.
However, the ways I've described have been inelegant, at best, and
painful, at worst.
This chapter contains things that make the
writing of makefiles easier and the makefiles themselves shorter and
easier to modify (and, occasionally, simpler). In this chapter, I
assume you are somewhat more
familiar with Sprite (or UNIX, if that's what you're using) than I did
in chapter 2, just so you're on your toes.
So without further ado...
.xH 2 Transformation Rules
.LP
As you know, a file's name consists of two parts: a base name, which
gives some hint as to the contents of the file, and a suffix, which
usually indicates the format of the file.
Over the years, as
.UX
has developed,
naming conventions, with regard to suffixes, have also developed that have
become almost as incontrovertible as Law. E.g. a file ending in
.CW .c
is assumed to contain C source code; one with a
.CW .o
suffix is assumed to be a compiled, relocatable object file that may
be linked into any program; a file with a
.CW .ms
suffix is usually a text file to be processed by Troff with the \-ms
macro package, and so on.
One of the best aspects of both Make and PMake comes from their
understanding of how the suffix of a file pertains to its contents and
their ability to do things with a file based soley on its suffix. This
ability comes from something known as a transformation rule. A
transformation rule specifies how to change a file with one suffix
into a file with another suffix.
.LP
A transformation rule looks much like a dependency line, except the
target is made of two known suffixes stuck together. Suffixes are made
known to PMake by placing them as sources on a dependency line whose
target is the special target
.CW .SUFFIXES .
E.g.
.DS
\&.SUFFIXES       : .o .c
\&.c.o            :
        $(CC) $(CFLAGS) -c $(.IMPSRC)