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 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          -a      Assume all targets to be out of date.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, 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

     MK(1)                                                       MK(1)

          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 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.  Lines beginning with <| fol-
          lowed by a file name are replaced by the output of the exe-
          cution 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

     MK(1)                                                       MK(1)

               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 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 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, 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.

          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 .

     MK(1)                                                       MK(1)

          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 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 /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:

     MK(1)                                                       MK(1)

          $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.

          $nproc        the process slot for this recipe.  It satis-
                        fies 0≤$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
                        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 rc 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.c
               foo: $bar
                       $CC -o foo $bar
               bar=b.c

          will compile b.c into foo, if a.c is newer than foo.

     MK(1)                                                       MK(1)

        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 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 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

     MK(1)                                                       MK(1)

          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

     MK(1)                                                       MK(1)

          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 print-
          ing.  Don't trust what's printed; rely on what the shell
          does.