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MK(10.1)							      MK(10.1)

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 contains a rule for
       each target that identifies the files and other targets upon  which  it
       depends	and  an	 rc(10.1) 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	speci‐
       fied,  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:

       -a      Assume all targets to be out  of	 date.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 build‐
	       ing, 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  exe‐
	       cuting 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 rc script.  Each line
       of the recipe must begin with white space.  A rule takes the form

	      target: prereq1 prereq2
		      rc 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 2c(10.1)
       might be:

	      %.2:    %.c
		      2c $stem.c
		      2l -o $stem $stem.2

       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.
       Blank lines and comments, which run from unquoted # characters  to  the
       following  newline, are deleted.	 The character sequence backslash-new‐
       line 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(10.1).

       Assignments and rules are distinguished by the  first  unquoted	occur‐
       rence of : (rule) or = (assignment).

       A  later rule may modify or override an existing rule under the follow‐
       ing 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 rc environment variables.	A legal	 reference  of
       the  form  $OBJ	or ${name} is expanded as in rc(10.1).	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 rc but without the  sur‐
       rounding	 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.

       It is recommended that mkfiles start with

	      </$objtype/mkfile

       to  set	CC, LD, AS, O, ALEF, YACC, and MK to values appropriate to the
       target architecture (see the examples below).

       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 vari‐
       ables 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 prerequi‐
       sites.  Once the recipe for a target has executed, the target  is  con‐
       sidered 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 ini‐
       tially 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.	Other‐
       wise, 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 prereq‐
       uisites 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 over‐
       rides this special treatment.

       Files may be made in any order that  respects  the  preceding  restric‐
       tions.

       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	 plat‐
       form - typically /bin/sh or /bin/rc.  The appropriate value is automat‐
       ically 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.

       $nproc	     the  process  slot	 for  this   recipe.	It   satisfies
		     0≤$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 are set to the cor‐
		     responding 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 exe‐
       cute 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
		      $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.  Cur‐
       rently, the only aggregates supported are ar(10.1) archives.

   Attributes
       The colon separating the target from the prerequisites may  be  immedi‐
       ately 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 rc -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	propa‐
	      gated 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	 regu‐
	      lar  expression  as defined in regexp(6).	 The prerequisites may
	      contain references to subexpressions in form \n, as in the  sub‐
	      stitute command of sed(10.1).

       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  dis‐
	      tinct from files of the same name.

EXAMPLES
       A simple mkfile to compile a program:

	      </$objtype/mkfile

	      prog:   a.$O b.$O c.$O
		  $LD $CFLAGS -o $target $prereq

	      %.$O:   %.c
		  $CC $stem.c

       Override flag settings in the mkfile:

	      % mk target 'CFLAGS=-S -w'

       To get the prerequisites for an aggregate:

	      % membername 'libc.a(read.2)' 'libc.a(write.2)'
	      read.2 write.2

       Maintain a library:

	      libc.a(%.$O):N: %.$O
	      libc.a: libc.a(abs.$O) libc.a(access.$O) libc.a(alarm.$O) ...
		  names=`{membername $newprereq}
		  ar r libc.a $names && rm $names

       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(10.1)  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
       /utils/mk

SEE ALSO
       rc(10.1), 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 tar‐
       get.
       Seemingly appropriate input like CFLAGS=-DHZ=60 is parsed as  an	 erro‐
       neous 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.

								      MK(10.1)
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