|
Mk uses the dependency rules specified in mkfile to control the
update (usually by compilation) of targets (usually files) from
the source files upon which they depend. The mkfile (default mkfile)
contains a rule for each target that identifies the files and
other targets upon which it depends and an sh(1) script, a recipe,
to update the target. The script is
run if the target does not exist or if it is older than any of
the files it depends on. Mkfile may also contain meta-rules that
define actions for updating implicit targets. If no target is
specified, the target of the first rule (not meta-rule) in mkfile
is updated.
The environment variable $NPROC determines how many targets may
be updated simultaneously; Some operating systems, e.g., Plan
9, set $NPROC automatically to the number of CPUs on the current
machine.
Options are:
−a Assume all targets to be out of date. Thus, everything is updated.
−d[egp]Produce debugging output (p is for parsing, g for graph
building, e for execution).
−e Explain why each target is made.
−i Force any missing intermediate targets to be made.
−k Do as much work as possible in the face of errors.
−n Print, but do not execute, the commands needed to update the
targets.
−s Make the command line arguments sequentially rather than in
parallel.
−t Touch (update the modified date of) file targets, without executing
any recipes.
−wtarget1,target2,...
| |
| |
Pretend the modify time for each target is the current time; useful
in conjunction with −n to learn what updates would be triggered
by modifying the targets.
|
|
The mkfile
A mkfile consists of assignments (described under ‘Environment’)
and rules. A rule contains targets and a tail. A target is a literal
string and is normally a file name. The tail contains zero or
more prerequisites and an optional recipe, which is an shell script.
Each line of the recipe must begin with white space. A rule takes
the form
| |
target: prereq1 prereq2
| |
recipe using prereq1, prereq2 to build target
|
|
When the recipe is executed, the first character on every line
is elided.
After the colon on the target line, a rule may specify attributes,
described below.
A meta-rule has a target of the form A%B where A and B are (possibly
empty) strings. A meta-rule acts as a rule for any potential target
whose name matches A%B with % replaced by an arbitrary string,
called the stem. In interpreting a meta-rule, the stem is substituted
for all occurrences of % in the prerequisite names. In the recipe
of a meta-rule, the
environment variable $stem contains the string matched by the
%. For example, a meta-rule to compile a C program using 9c(1)
might be:
| |
%: %.c
| |
9c −c $stem.c
9l −o $stem $stem.o
|
|
Meta-rules may contain an ampersand & rather than a percent sign
%. A % matches a maximal length string of any characters; an &
matches a maximal length string of any characters except period
or slash.
The text of the mkfile is processed as follows. Lines beginning
with < followed by a file name are replaced by the contents of
the named file. Lines beginning with <| followed by a file name
are replaced by the output of the execution of the named file.
Blank lines and comments, which run from unquoted # characters
to the following newline, are
deleted. The character sequence backslash-newline is deleted,
so long lines in mkfile may be folded. Non-recipe lines are processed
by substituting for `{command} the output of the command when
run by sh. References to variables are replaced by the variables’
values. Special characters may be quoted using single quotes ''
as in sh(1).
Assignments and rules are distinguished by the first unquoted
occurrence of : (rule) or = (assignment).
A later rule may modify or override an existing rule under the
following conditions:
– If the targets of the rules exactly match and one rule contains
only a prerequisite clause and no recipe, the clause is added
to the prerequisites of the other rule. If either or both targets
are virtual, the recipe is always executed.
– If the targets of the rules match exactly and the prerequisites
do not match and both rules contain recipes, mk reports an “ambiguous
recipe” error.
– If the target and prerequisites of both rules match exactly, the
second rule overrides the first.
Environment
Rules may make use of shell environment variables. A legal reference
of the form $OBJ or ${name} is expanded as in sh(1). A reference
of the form ${name:A%B=C%D}, where A, B, C, D are (possibly empty)
strings, has the value formed by expanding $name and substituting
C for A and D for B in each word in $name that matches pattern
A%B.
Variables can be set by assignments of the form
Blanks in the value break it into words. Such variables are exported
to the environment of recipes as they are executed, unless U,
the only legal attribute attr, is present. The initial value of
a variable is taken from (in increasing order of precedence) the
default values below, mk’s environment, the mkfiles, and any command
line assignment as an
argument to mk. A variable assignment argument overrides the first
(but not any subsequent) assignment to that variable.
The variable MKFLAGS contains all the option arguments (arguments
starting with − or containing =) and MKARGS contains all the targets
in the call to mk.
The variable MKSHELL contains the shell command line mk uses to
run recipes. If the first word of the command ends in rc or rcsh,
mk uses rc(1)’s quoting rules; otherwise it uses sh(1)’s. The
MKSHELL variable is consulted when the mkfile is read, not when
it is executed, so that different shells can be used within a
single mkfile:
| |
MKSHELL=$PLAN9/bin/rc
use−rc:V:
MKSHELL=sh
use−sh:V:
| |
for i in a b c; do echo $i; done
|
|
Mkfiles included via < or <| (q.v.) see their own private copy of
MKSHELL, which always starts set to sh .
Dynamic information may be included in the mkfile by using a line
of the form
This runs the command command with the given arguments args and
pipes its standard output to mk to be included as part of the
mkfile. For instance, the Inferno kernels use this technique to
run a shell command with an awk script and a configuration file
as arguments in order for the awk script to process the file and
output a set of variables and their
values.
Execution
During execution, mk determines which targets must be updated,
and in what order, to build the names specified on the command
line. It then runs the associated recipes.
A target is considered up to date if it has no prerequisites or
if all its prerequisites are up to date and it is newer than all
its prerequisites. Once the recipe for a target has executed,
the target is considered up to date.
The date stamp used to determine if a target is up to date is
computed differently for different types of targets. If a target
is virtual (the target of a rule with the V attribute), its date
stamp is initially zero; when the target is updated the date stamp
is set to the most recent date stamp of its prerequisites. Otherwise,
if a target does not exist as a file, its date
stamp is set to the most recent date stamp of its prerequisites,
or zero if it has no prerequisites. Otherwise, the target is the
name of a file and the target’s date stamp is always that file’s
modification date. The date stamp is computed when the target
is needed in the execution of a rule; it is not a static value.
Nonexistent targets that have prerequisites and are themselves
prerequisites are treated specially. Such a target t is given
the date stamp of its most recent prerequisite and if this causes
all the targets which have t as a prerequisite to be up to date,
t is considered up to date. Otherwise, t is made in the normal
fashion. The −i flag overrides this special
treatment.
Files may be made in any order that respects the preceding restrictions.
A recipe is executed by supplying the recipe as standard input
to the command /bin/sh. (Note that unlike make, mk feeds the entire
recipe to the shell rather than running each line of the recipe
separately.) The environment is augmented by the following variables:
$alltargetall the targets of this rule.
$newprereqthe prerequisites that caused this rule to execute.
$newmemberthe prerequisites that are members of an aggregate that
caused this rule to execute. When the prerequisites of a rule
are members of an aggregate, $newprereq contains the name of the
aggregate and out of date members, while $newmember contains only
the name of the members.
$nproc the process slot for this recipe. It satisfies 0≤$nproc<$NPROC.
$pid the process id for the mk executing the recipe.
$prereq all the prerequisites for this rule.
$stem if this is a meta-rule, $stem is the string that matched
% or &. Otherwise, it is empty. For regular expression meta-rules
(see below), the variables stem0, ..., stem9 are set to the corresponding
subexpressions.
$target the targets for this rule that need to be remade.
These variables are available only during the execution of a recipe,
not while evaluating the mkfile.
Unless the rule has the Q attribute, the recipe is printed prior
to execution with recognizable environment variables expanded.
Commands returning error status cause mk to terminate.
Recipes and backquoted rc commands in places such as assignments
execute in a copy of mk’s environment; changes they make to environment
variables are not visible from mk.
Variable substitution in a rule is done when the rule is read;
variable substitution in the recipe is done when the recipe is
executed. For example:
| |
bar=a.c
foo: $bar
bar=b.c
|
will compile b.c into foo, if a.c is newer than foo.
Aggregates
Names of the form a(b) refer to member b of the aggregate a. Currently,
the only aggregates supported are 9ar (see 9c(1)) archives.
Attributes
The colon separating the target from the prerequisites may be
immediately followed by attributes and another colon. The attributes
are:
D If the recipe exits with a non-null status, the target is deleted.
E Continue execution if the recipe draws errors.
N If there is no recipe, the target has its time updated.
n The rule is a meta-rule that cannot be a target of a virtual
rule. Only files match the pattern in the target.
P The characters after the P until the terminating : are taken
as a program name. It will be invoked as sh −c prog 'arg1' 'arg2'
and should return a zero exit status if and only if arg1 is up
to date with respect to arg2. Date stamps are still propagated
in the normal way.
Q The recipe is not printed prior to execution.
R The rule is a meta-rule using regular expressions. In the rule,
% has no special meaning. The target is interpreted as a regular
expression as defined in regexp(7). The prerequisites may contain
references to subexpressions in form \n, as in the substitute
command of sed(1).
U The targets are considered to have been updated even if the recipe
did not do so.
V The targets of this rule are marked as virtual. They are distinct
from files of the same name.
|
