NAME
mk, membername – maintain (make) related files |
SYNOPSIS
mk [ –f mkfile ] ... [ option ... ] [ target ... ]
membername aggregate ... |
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 an rc(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; Plan 9 sets $NPROC automatically to the number of CPUs on the current machine.
Options are:
The mkfile
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 8c(1) might be:
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 rc. References to variables are replaced by the variables' values. Special characters may be quoted using single quotes '' as in rc(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: Environment
Variables can be set by assignments of the form
The variable MKFLAGS contains all the option arguments (arguments starting with – or containing =) and MKARGS contains all the targets in the call to mk.
It is recommended that mkfiles start with
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
$alltarget
$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 nonempty status (see intro(1)) 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:
Aggregates Attributes |
EXAMPLES
A simple mkfile to compile a program: <
|
SOURCE
/sys/src/cmd/mk |
SEE ALSO
rc(1), regexp(6) A. Hume, ``Mk: a Successor to Make''.
Andrew G. Hume and Bob Flandrena, ``Maintaining Files on Plan
9 with Mk''. |
BUGS
Identical recipes for regular expression meta–rules only have one
target. Seemingly appropriate input like CFLAGS=–DHZ=60 is parsed as an erroneous attribute; correct it by inserting a space after the first =.
The recipes printed by mk before being passed to rc for execution
are sometimes erroneously expanded for printing. Don't trust what's
printed; rely on what rc does. |