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 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-a Assume all targets to be out of date.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 $name that matches pattern A%B.
Variables can be set by assignments of the form
var=[attr=]value
Blanks in the value break it into words. Such variables are exported
to the environment of recipes as they are executed, unless U, the only
legal attribute attr, is present. The initial value of a variable is
taken from (in increasing order of precedence) the default values
below, mks environment, the mkfiles, and any command line assignment
as an argument to mk. A variable assignment argument overrides the
first (but not any subsequent) assignment to that variable.
The variable MKFLAGS contains all the option arguments (arguments
starting with or containing and MKARGS contains all the targets in the
call to mk.
The variable MKSHELL contains the shell command line mk uses to run
recipes. If the first word of the command ends in rc or rcsh, mk uses
rc(1)’s quoting rules; otherwise it uses sh(1)’s. The MKSHELL variable
is consulted when the mkfile is read, not when it is executed, so that
different shells can be used within a single mkfile:
MKSHELL=$PLAN9/bin/rc use-rc:V: for(i in a b c) echo $i
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
<|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 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:
$alltarget all the targets of this rule.
$newprereq the prerequisites that caused this rule to execute.
$newmember the 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.
$nproc the process slot for this recipe. It satisfies
0â¤$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 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 mks 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
$CC -o foo $bar bar=b.c
will compile b.c into foo, if a.c is newer than foo.
Aggregates
Names of the form a(b) refer to member b of the aggregate a.
Currently, the only aggregates supported are 9ar (see 9c(1)) archives.
Attributes
The colon separating the target from the prerequisites may be
immediately followed by attributes and another colon. The attributes
are:
D If the recipe exits with a non-null status, the target is
deleted.
E Continue execution if the recipe draws errors.
N If there is no recipe, the target has its time updated.
n The rule is a meta-rule that cannot be a target of a virtual
rule. Only files match the pattern in the target.
P The characters after the P until the terminating : are taken as
a program name. It will be invoked as sh -c prog ’arg1’ ’arg2’
and should return a zero exit status if and only if arg1 is up
to date with respect to arg2. Date stamps are still propagated
in the normal way.
Q The recipe is not printed prior to execution.
R The rule is a meta-rule using regular expressions. In the rule,
% has no special meaning. The target is interpreted as a
regular expression as defined in regexp(7). The prerequisites
may contain references to subexpressions in form \n, as in the
substitute command of sed(1).
U The targets are considered to have been updated even if the
recipe did not do so.
V The targets of this rule are marked as virtual. They are
distinct from files of the same name.
EXAMPLES
A simple mkfile to compile a program:
</$objtype/mkfile
prog: a.$O b.$O c.$O $LD $LDFLAGS -o $target $prereq
%.$O: %.c $CC $CFLAGS $stem.c
Override flag settings in the mkfile:
% mk target ’CFLAGS=-S -w’
Maintain a library:
libc.a(%.$O):N: %.$O libc.a: libc.a(abs.$O) libc.a(access.$O)
libc.a(alarm.$O) ... ar r libc.a $newmember
String expression variables to derive names from a master list:
NAMES=alloc arc bquote builtins expand main match mk var word
OBJ=${NAMES:%=%.$O}
Regular expression meta-rules:
([^/]*)/(.*)\.$O:R: \1/\2.c cd $stem1; $CC $CFLAGS
$stem2.c
A correct way to deal with yacc(1) grammars. The file lex.c includes
the file x.tab.h rather than y.tab.h in order to reflect changes in
content, not just modification time.
lex.$O: x.tab.h x.tab.h: y.tab.h cmp -s x.tab.h
y.tab.h || cp y.tab.h x.tab.h y.tab.c y.tab.h: gram.y
$YACC -d gram.y
The above example could also use the P attribute for the x.tab.h rule:
x.tab.h:Pcmp -s: y.tab.h cp y.tab.h x.tab.h
SOURCE
/src/cmd/mk
SEE ALSO
sh(1), regexp(7)
A. Hume, ‘‘Mk: a Successor to Make’’ (Tenth Edition Research Unix
Manuals).
Andrew G. Hume and Bob Flandrena, ‘‘Maintaining Files on Plan 9 with
Mk’’. DOCPREFIX/doc/mk.pdf
HISTORY
Andrew Hume wrote mk for Tenth Edition Research Unix. It was later
ported to Plan 9. This software is a port of the Plan 9 version back
to Unix.
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 the shell for
execution are sometimes erroneously expanded for printing. Don’t trust
what’s printed; rely on what the shell does.
MK(1)