MK(1) MK(1)
NAME
mk - maintain (make) related files
SYNOPSIS
mk [ -f mkfile ] ... [ option ... ] [ target ... ]
DESCRIPTION
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 a 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;
the default value is 1.
Options are:
-a Assume all targets to be out of date. Thus, every-
thing 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 cur-
rent 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 `Environ-
ment') and rules. A rule contains targets and a tail. A tar-
get is a literal string and is normally a file name. The
tail contains zero or more prerequisites and an optional
recipe, which is a sh script. Each line of the recipe must
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begin with white space. A rule takes the form
target: prereq1 prereq2
sh 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 limbo pro-
gram anmd install it might be:
%.dis: %.b
limbo $stem.b
cp $stem.dis /dis
Meta-rules may contain an ampersand & rather than a percent
sign %. A % matches a maximal length string of any charac-
ters; 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. 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 out-
put 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.
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- If the targets of the rules match exactly and the pre-
requisites 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 sh 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
var=[attr=]value
Blanks in the value break it into words, as in sh but with-
out the surrounding parentheses. 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 environ-
ment, 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.
Dynamic information may be included in the mkfile by using a
line of the form
<| command args
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 file /os/sa1100/mkfile uses
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
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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 tar-
get 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 pre-
requisites. 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 them-
selves 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 prerequi-
site to be up to date, t is considered up to date. Other-
wise, t is made in the normal fashion. The -i flag over-
rides 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
$SHELL -e -I
where the SHELL variable is the appropriate shell on the
current platform - typically /dis/sh The appropriate value
is automatically supplied in the Inferno build environment.
The -e is omitted if the E attribute is set. The environment
is augmented by the following variables:
$alltarget all the targets of this rule.
$newprereq the prerequisites that caused this rule to
execute.
$nproc the process slot for this recipe. It satis-
fies 0≤$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
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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 ter-
minate.
Recipes and backquoted sh commands in places such as assign-
ments 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.b
foo: $bar
limbo -o foo $bar
bar=b.b
will compile b.b into foo, if a.b is newer than foo.
Aggregates
Names of the form a(b) refer to member b of the aggregate a.
Currently, there are no aggregates supported under Inferno.
Attributes
The colon separating the target from the prerequisites may
be immediately followed by attributes and another colon.
The attributes are:
D If the recipe exits with a non-null status, the target
is deleted.
E Continue execution if the recipe draws errors.
N If there is no recipe, the target has its time updated.
n The rule is a meta-rule that cannot be a target of a
virtual rule. Only files match the pattern in the tar-
get.
P The characters after the P until the terminating : are
taken as a program name. It will be invoked as sh -c
prog 'arg1' 'arg2' and should return a null exit status
if and only if arg1 is not out of date with respect to
arg2. Date stamps are still propagated in the normal
way.
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Q The recipe is not printed prior to execution.
R The rule is a meta-rule using regular expressions. In
the rule, % has no special meaning. The target is
interpreted as a regular expression as defined in
regexp(6). The prerequisites may contain references to
subexpressions in form \n, as in the substitute command
of sed(1).
U The targets are considered to have been updated even if
the recipe did not do so.
V The targets of this rule are marked as virtual. They
are distinct from files of the same name.
EXAMPLES
A simple mkfile to compile and install limbo programs:
O=dis
prog: a.$O b.$O c.$O
cp $prereq /dis
%.$O: %.b
limbo $stem.b
String expression variables to derive names from a master
list:
NAMES=alloc arc bquote builtins expand main match mk var word
OBJ=${NAMES:%=%.$O}
Regular expression meta-rules:
([^/]*)/(.*)\.dis:R: \1/\2.b
cd $stem1; limbo $stem2.b
SOURCE
/appl/cmd/mk
SEE ALSO
sh(1), regexp(6)
A. Hume, ``Mk: a Successor to Make''.
Bob Flandrena, ``Plan 9 Mkfiles''.
BUGS
Identical recipes for regular expression meta-rules only
have one target.
The recipes printed by mk before being passed to sh for exe-
cution are sometimes erroneously expanded for printing.
Don't trust what's printed; rely on what sh does.
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