freebsd-dev/contrib/bmake/make.1

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.\"	from: @(#)make.1	8.4 (Berkeley) 3/19/94
.\"
.Dd May 10, 2023
.Dt MAKE 1
.Os
.Sh NAME
.Nm make
.Nd maintain program dependencies
.Sh SYNOPSIS
.Nm
.Op Fl BeikNnqrSstWwX
.Op Fl C Ar directory
.Op Fl D Ar variable
.Op Fl d Ar flags
.Op Fl f Ar makefile
.Op Fl I Ar directory
.Op Fl J Ar private
.Op Fl j Ar max_jobs
.Op Fl m Ar directory
.Op Fl T Ar file
.Op Fl V Ar variable
.Op Fl v Ar variable
.Op Ar variable\| Ns Cm \&= Ns Ar value
.Op Ar target No ...
.Sh DESCRIPTION
.Nm
is a program designed to simplify the maintenance of other programs.
Its input is a list of specifications as to the files upon which programs
and other files depend.
If no
.Fl f Ar makefile
option is given,
.Nm
tries to open
.Sq Pa makefile
then
.Sq Pa Makefile
in order to find the specifications.
If the file
.Sq Pa .depend
exists, it is read, see
.Xr mkdep 1 .
.Pp
This manual page is intended as a reference document only.
For a more thorough description of
.Nm
and makefiles, please refer to
.%T "PMake \- A Tutorial"
(from 1993).
.Pp
.Nm
prepends the contents of the
.Ev MAKEFLAGS
environment variable to the command line arguments before parsing them.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl B
Try to be backwards compatible by executing a single shell per command and
by making the sources of a dependency line in sequence.
.It Fl C Ar directory
Change to
.Ar directory
before reading the makefiles or doing anything else.
If multiple
.Fl C
options are specified, each is interpreted relative to the previous one:
.Fl C Pa / Fl C Pa etc
is equivalent to
.Fl C Pa /etc .
.It Fl D Ar variable
Define
.Ar variable
to be 1, in the global scope.
.It Fl d Oo Cm \- Oc Ns Ar flags
Turn on debugging, and specify which portions of
.Nm
are to print debugging information.
Unless the flags are preceded by
.Ql \- ,
they are added to the
.Ev MAKEFLAGS
environment variable and are passed on to any child make processes.
By default, debugging information is printed to standard error,
but this can be changed using the
.Cm F
debugging flag.
The debugging output is always unbuffered; in addition, if debugging
is enabled but debugging output is not directed to standard output,
the standard output is line buffered.
The available
.Ar flags
are:
.Bl -tag -width Ds
.It Cm A
Print all possible debugging information;
equivalent to specifying all of the debugging flags.
.It Cm a
Print debugging information about archive searching and caching.
.It Cm C
Print debugging information about the current working directory.
.It Cm c
Print debugging information about conditional evaluation.
.It Cm d
Print debugging information about directory searching and caching.
.It Cm e
Print debugging information about failed commands and targets.
.It Cm F Ns Oo Cm \&+ Oc Ns Ar filename
Specify where debugging output is written.
This must be the last flag, because it consumes the remainder of
the argument.
If the character immediately after the
.Cm F
flag is
.Ql \&+ ,
the file is opened in append mode;
otherwise the file is overwritten.
If the file name is
.Ql stdout
or
.Ql stderr ,
debugging output is written to the standard output or standard error output
respectively (and the
.Ql \&+
option has no effect).
Otherwise, the output is written to the named file.
If the file name ends with
.Ql .%d ,
the
.Ql %d
is replaced by the pid.
.It Cm f
Print debugging information about loop evaluation.
.It Cm g1
Print the input graph before making anything.
.It Cm g2
Print the input graph after making everything, or before exiting
on error.
.It Cm g3
Print the input graph before exiting on error.
.It Cm h
Print debugging information about hash table operations.
.It Cm j
Print debugging information about running multiple shells.
.It Cm L
Turn on lint checks.
This throws errors for variable assignments that do not parse correctly,
at the time of assignment, so the file and line number are available.
.It Cm l
Print commands in Makefiles regardless of whether or not they are prefixed by
.Ql @
or other
.Dq quiet
flags.
Also known as
.Dq loud
behavior.
.It Cm M
Print debugging information about
.Dq meta
mode decisions about targets.
.It Cm m
Print debugging information about making targets, including modification
dates.
.It Cm n
Don't delete the temporary command scripts created when running commands.
These temporary scripts are created in the directory
referred to by the
.Ev TMPDIR
environment variable, or in
.Pa /tmp
if
.Ev TMPDIR
is unset or set to the empty string.
The temporary scripts are created by
.Xr mkstemp 3 ,
and have names of the form
.Pa makeXXXXXX .
.Em NOTE :
This can create many files in
.Ev TMPDIR
or
.Pa /tmp ,
so use with care.
.It Cm p
Print debugging information about makefile parsing.
.It Cm s
Print debugging information about suffix-transformation rules.
.It Cm t
Print debugging information about target list maintenance.
.It Cm V
Force the
.Fl V
option to print raw values of variables,
overriding the default behavior set via
.Va .MAKE.EXPAND_VARIABLES .
.It Cm v
Print debugging information about variable assignment and expansion.
.It Cm x
Run shell commands with
.Fl x
so the actual commands are printed as they are executed.
.El
.It Fl e
Let environment variables override global variables within makefiles.
.It Fl f Ar makefile
Specify a makefile to read instead of the default
.Pa makefile
or
.Pa Makefile .
If
.Ar makefile
is
.Ql \&- ,
standard input is read.
Multiple makefiles may be specified, and are read in the order specified.
.It Fl I Ar directory
Specify a directory in which to search for makefiles and included makefiles.
The system makefile directory (or directories, see the
.Fl m
option) is automatically included as part of this list.
.It Fl i
Ignore non-zero exit of shell commands in the makefile.
Equivalent to specifying
.Ql \&-
before each command line in the makefile.
.It Fl J Ar private
This option should
.Em not
be specified by the user.
.Pp
When the
.Fl j
option is in use in a recursive build, this option is passed by a make
to child makes to allow all the make processes in the build to
cooperate to avoid overloading the system.
.It Fl j Ar max_jobs
Specify the maximum number of jobs that
.Nm
may have running at any one time.
The value of
.Ar max_jobs
is saved in
.Va .MAKE.JOBS .
Turns compatibility mode off, unless the
.Fl B
option is also specified.
When compatibility mode is off, all commands associated with a
target are executed in a single shell invocation as opposed to the
traditional one shell invocation per line.
This can break traditional scripts which change directories on each
command invocation and then expect to start with a fresh environment
on the next line.
It is more efficient to correct the scripts rather than turn backwards
compatibility on.
.Pp
A job token pool with
.Ar max_jobs
tokens is used to control the total number of jobs running.
Each instance of
.Nm
will wait for a token from the pool before running a new job.
.It Fl k
Continue processing after errors are encountered, but only on those targets
that do not depend on the target whose creation caused the error.
.It Fl m Ar directory
Specify a directory in which to search for
.Pa sys.mk
and makefiles included via the
.Li \&< Ns Ar file Ns Li \&> Ns -style
include statement.
The
.Fl m
option can be used multiple times to form a search path.
This path overrides the default system include path
.Pa /usr/share/mk .
Furthermore, the system include path is appended to the search path used for
.Li \*q Ns Ar file Ns Li \*q Ns -style
include statements (see the
.Fl I
option).
The system include path can be referenced via the read-only variable
.Va .SYSPATH .
.Pp
If a directory name in the
.Fl m
argument (or the
.Ev MAKESYSPATH
environment variable) starts with the string
.Ql \&.../ ,
.Nm
searches for the specified file or directory named in the remaining part
of the argument string.
The search starts with the current directory
and then works upward towards the root of the file system.
If the search is successful, the resulting directory replaces the
.Ql \&.../
specification in the
.Fl m
argument.
This feature allows
.Nm
to easily search in the current source tree for customized
.Pa sys.mk
files (e.g., by using
.Ql \&.../mk/sys.mk
as an argument).
.It Fl n
Display the commands that would have been executed, but do not
actually execute them unless the target depends on the
.Va .MAKE
special source (see below) or the command is prefixed with
.Sq Cm + .
.It Fl N
Display the commands that would have been executed,
but do not actually execute any of them;
useful for debugging top-level makefiles
without descending into subdirectories.
.It Fl q
Do not execute any commands,
instead exit 0 if the specified targets are up to date, and 1 otherwise.
.It Fl r
Do not use the built-in rules specified in the system makefile.
.It Fl S
Stop processing if an error is encountered.
This is the default behavior and the opposite of
.Fl k .
.It Fl s
Do not echo any commands as they are executed.
Equivalent to specifying
.Sq Ic @
before each command line in the makefile.
.It Fl T Ar tracefile
When used with the
.Fl j
flag,
append a trace record to
.Ar tracefile
for each job started and completed.
.It Fl t
Rather than re-building a target as specified in the makefile, create it
or update its modification time to make it appear up-to-date.
.It Fl V Ar variable
Print the value of
.Ar variable .
Do not build any targets.
Multiple instances of this option may be specified;
the variables are printed one per line,
with a blank line for each null or undefined variable.
The value printed is extracted from the global scope after all
makefiles have been read.
.Pp
By default, the raw variable contents (which may
include additional unexpanded variable references) are shown.
If
.Ar variable
contains a
.Ql \&$ ,
it is not interpreted as a variable name but rather as an expression.
Its value is expanded before printing.
The value is also expanded before printing if
.Va .MAKE.EXPAND_VARIABLES
is set to true and the
.Fl dV
option has not been used to override it.
.Pp
Note that loop-local and target-local variables, as well as values
taken temporarily by global variables during makefile processing, are
not accessible via this option.
The
.Fl dv
debug mode can be used to see these at the cost of generating
substantial extraneous output.
.It Fl v Ar variable
Like
.Fl V ,
but all printed variables are always expanded to their complete value.
The last occurrence of
.Fl V
or
.Fl v
decides whether all variables are expanded or not.
.It Fl W
Treat any warnings during makefile parsing as errors.
.It Fl w
Print entering and leaving directory messages, pre and post processing.
.It Fl X
Don't export variables passed on the command line to the environment
individually.
Variables passed on the command line are still exported via the
.Ev MAKEFLAGS
environment variable.
This option may be useful on systems which have a small limit on the
size of command arguments.
.It Ar variable\| Ns Cm \&= Ns Ar value
Set the value of the variable
.Ar variable
to
.Ar value .
Normally, all values passed on the command line are also exported to
sub-makes in the environment.
The
.Fl X
flag disables this behavior.
Variable assignments should follow options for POSIX compatibility
but no ordering is enforced.
.El
.Pp
There are several different types of lines in a makefile: dependency
specifications, shell commands, variable assignments, include statements,
conditional directives, for loops, other directives, and comments.
.Pp
Lines may be continued from one line to the next
by ending them with a backslash
.Pq Ql \e .
The trailing newline character and initial whitespace on the following
line are compressed into a single space.
.Sh FILE DEPENDENCY SPECIFICATIONS
Dependency lines consist of one or more targets, an operator, and zero
or more sources.
This creates a relationship where the targets
.Dq depend
on the sources and are customarily created from them.
A target is considered out of date if it does not exist,
or if its modification time is less than that of any of its sources.
An out-of-date target is re-created, but not until all sources
have been examined and themselves re-created as needed.
Three operators may be used:
.Bl -tag -width flag
.It Ic \&:
Many dependency lines may name this target but only one may have
attached shell commands.
All sources named in all dependency lines are considered together,
and if needed the attached shell commands are run to create or
re-create the target.
If
.Nm
is interrupted, the target is removed.
.It Ic \&!
The same, but the target is always re-created whether or not it is out
of date.
.It Ic \&::
Any dependency line may have attached shell commands, but each one
is handled independently: its sources are considered and the attached
shell commands are run if the target is out of date with respect to
(only) those sources.
Thus, different groups of the attached shell commands may be run
depending on the circumstances.
Furthermore, unlike
.Ic \&: ,
for dependency lines with no sources, the attached shell
commands are always run.
Also unlike
.Ic \&: ,
the target is not removed if
.Nm
is interrupted.
.El
.Pp
All dependency lines mentioning a particular target must use the same
operator.
.Pp
Targets and sources may contain the shell wildcard values
.Ql \&? ,
.Ql * ,
.Ql [] ,
and
.Ql {} .
The values
.Ql \&? ,
.Ql * ,
and
.Ql []
may only be used as part of the final component of the target or source,
and only match existing files.
The value
.Ql {}
need not necessarily be used to describe existing files.
Expansion is in directory order, not alphabetically as done in the shell.
.Sh SHELL COMMANDS
Each target may have associated with it one or more lines of shell commands,
normally used to create the target.
Each of the lines in this script
.Em must
be preceded by a tab.
(For historical reasons, spaces are not accepted.)
While targets can occur in many dependency lines if desired,
by default only one of these rules may be followed by a creation script.
If the
.Sq Ic \&::
operator is used, however, all rules may include scripts,
and the respective scripts are executed in the order found.
.Pp
Each line is treated as a separate shell command,
unless the end of line is escaped with a backslash
.Ql \e ,
in which case that line and the next are combined.
If the first characters of the command are any combination of
.Sq Ic @ ,
.Sq Ic + ,
or
.Sq Ic \- ,
the command is treated specially.
.Bl -tag -offset indent -width indent
.It Ic @
causes the command not to be echoed before it is executed.
.It Ic +
causes the command to be executed even when
.Fl n
is given.
This is similar to the effect of the
.Va .MAKE
special source,
except that the effect can be limited to a single line of a script.
.It Ic \-
in compatibility mode
causes any non-zero exit status of the command line to be ignored.
.El
.Pp
When
.Nm
is run in jobs mode with
.Fl j Ar max_jobs ,
the entire script for the target is fed to a single instance of the shell.
In compatibility (non-jobs) mode, each command is run in a separate process.
If the command contains any shell meta characters
.Pq Ql #=|^(){};&<>*?[]:$`\e\en ,
it is passed to the shell; otherwise
.Nm
attempts direct execution.
If a line starts with
.Sq Ic \-
and the shell has ErrCtl enabled,
failure of the command line is ignored as in compatibility mode.
Otherwise
.Sq Ic \-
affects the entire job;
the script stops at the first command line that fails,
but the target is not deemed to have failed.
.Pp
Makefiles should be written so that the mode of
.Nm
operation does not change their behavior.
For example, any command which uses
.Dq cd
or
.Dq chdir
without the intention of changing the directory for subsequent commands
should be put in parentheses so it executes in a subshell.
To force the use of a single shell, escape the line breaks so as to make
the whole script one command.
For example:
.Bd -literal -offset indent
avoid-chdir-side-effects:
	@echo "Building $@ in $$(pwd)"
	@(cd ${.CURDIR} && ${MAKE} $@)
	@echo "Back in $$(pwd)"

ensure-one-shell-regardless-of-mode:
	@echo "Building $@ in $$(pwd)"; \e
	(cd ${.CURDIR} && ${MAKE} $@); \e
	echo "Back in $$(pwd)"
.Ed
.Pp
Since
.Nm
changes the current working directory to
.Sq Va .OBJDIR
before executing any targets,
each child process starts with that as its current working directory.
.Sh VARIABLE ASSIGNMENTS
Variables in make behave much like macros in the C preprocessor.
.Pp
Variable assignments have the form
.Sq Ar NAME Ar op Ar value ,
where:
.Bl -tag -offset Ds -width Ds
.It Ar NAME
is a single-word variable name,
consisting, by tradition, of all upper-case letters,
.It Ar op
is one of the variable assignment operators described below, and
.It Ar value
is interpreted according to the variable assignment operator.
.El
.Pp
Whitespace around
.Ar NAME ,
.Ar op
and
.Ar value
is discarded.
.Ss Variable assignment operators
The five operators that assign values to variables are:
.Bl -tag -width Ds
.It Ic \&=
Assign the value to the variable.
Any previous value is overwritten.
.It Ic \&+=
Append the value to the current value of the variable,
separating them by a single space.
.It Ic \&?=
Assign the value to the variable if it is not already defined.
.It Ic \&:=
Expand the value, then assign it to the variable.
.Pp
.Em NOTE :
References to undefined variables are
.Em not
expanded.
This can cause problems when variable modifiers are used.
.\" See var-op-expand.mk, the section with LATER and INDIRECT.
.It Ic \&!=
Expand the value and pass it to the shell for execution,
then assign the output from the child's standard output to the variable.
Any newlines in the result are replaced with spaces.
.El
.Ss Expansion of variables
In most contexts where variables are expanded,
.Ql \&$$
expands to a single dollar sign.
In other contexts (most variable modifiers, string literals in conditions),
.Ql \&\e$
expands to a single dollar sign.
.Pp
References to variables have the form
.Cm \&${ Ns Ar name Ns Oo Ns Cm \&: Ns Ar modifiers Oc Ns Cm \&}
or
.Cm \&$( Ns Ar name Ns Oo Ns Cm \&: Ns Ar modifiers Oc Ns Cm \&) .
If the variable name consists of only a single character
and the expression contains no modifiers,
the surrounding curly braces or parentheses are not required.
This shorter form is not recommended.
.Pp
If the variable name contains a dollar, the name itself is expanded first.
This allows almost arbitrary variable names, however names containing dollar,
braces, parentheses or whitespace are really best avoided.
.Pp
If the result of expanding a nested variable expression contains a dollar sign
.Pq Ql \&$ ,
the result is subject to further expansion.
.Pp
Variable substitution occurs at four distinct times, depending on where
the variable is being used.
.Bl -enum
.It
Variables in dependency lines are expanded as the line is read.
.It
Variables in conditionals are expanded individually,
but only as far as necessary to determine the result of the conditional.
.It
Variables in shell commands are expanded when the shell command is
executed.
.It
.Ic .for
loop index variables are expanded on each loop iteration.
Note that other variables are not expanded when composing the body of a loop,
so the following example code:
.Bd -literal -offset indent
\&.for i in 1 2 3
a+=     ${i}
j=      ${i}
b+=     ${j}
\&.endfor

all:
	@echo ${a}
	@echo ${b}
.Ed
.Pp
prints:
.Bd -literal -offset indent
1 2 3
3 3 3
.Ed
.Pp
After the loop is executed:
.Bl -tag -offset indent -width indent
.It Va a
contains
.Ql ${:U1} ${:U2} ${:U3} ,
which expands to
.Ql 1 2 3 .
.It Va j
contains
.Ql ${:U3} ,
which expands to
.Ql 3 .
.It Va b
contains
.Ql ${j} ${j} ${j} ,
which expands to
.Ql ${:U3} ${:U3} ${:U3}
and further to
.Ql 3 3 3 .
.El
.El
.Ss Variable classes
The four different classes of variables (in order of increasing precedence)
are:
.Bl -tag -width Ds
.It Environment variables
Variables defined as part of
.Nm Ns 's
environment.
.It Global variables
Variables defined in the makefile or in included makefiles.
.It Command line variables
Variables defined as part of the command line.
.It Local variables
Variables that are defined specific to a certain target.
.El
.Pp
Local variables can be set on a dependency line, unless
.Va .MAKE.TARGET_LOCAL_VARIABLES
is set to
.Ql false .
The rest of the line
(which already has had global variables expanded)
is the variable value.
For example:
.Bd -literal -offset indent
COMPILER_WRAPPERS= ccache distcc icecc

${OBJS}: .MAKE.META.CMP_FILTER=${COMPILER_WRAPPERS:S,^,N,}
.Ed
.Pp
Only the targets
.Ql ${OBJS}
are impacted by that filter (in
.Dq meta
mode) and
simply enabling/disabling any of the compiler wrappers does not render all
of those targets out-of-date.
.Pp
.Em NOTE :
target-local variable assignments behave differently in that;
.Bl -tag -width Ds -offset indent
.It Ic \&+=
Only appends to a previous local assignment
for the same target and variable.
.It Ic \&:=
Is redundant with respect to global variables,
which have already been expanded.
.El
.Pp
The seven built-in local variables are:
.Bl -tag -width ".Va .ARCHIVE" -offset indent
.It Va .ALLSRC
The list of all sources for this target; also known as
.Sq Va \&> .
.It Va .ARCHIVE
The name of the archive file; also known as
.Sq Va \&! .
.It Va .IMPSRC
In suffix-transformation rules, the name/path of the source from which the
target is to be transformed (the
.Dq implied
source); also known as
.Sq Va \&< .
It is not defined in explicit rules.
.It Va .MEMBER
The name of the archive member; also known as
.Sq Va % .
.It Va .OODATE
The list of sources for this target that were deemed out-of-date; also
known as
.Sq Va \&? .
.It Va .PREFIX
The name of the target with suffix (if declared in
.Ic .SUFFIXES )
removed; also known as
.Sq Va * .
.It Va .TARGET
The name of the target; also known as
.Sq Va @ .
For compatibility with other makes this is an alias for
.Va .ARCHIVE
in archive member rules.
.El
.Pp
The shorter forms
.Po
.Sq Va \&> ,
.Sq Va \&! ,
.Sq Va \&< ,
.Sq Va \&% ,
.Sq Va \&? ,
.Sq Va \&* ,
and
.Sq Va \&@
.Pc
are permitted for backward
compatibility with historical makefiles and legacy POSIX make and are
not recommended.
.Pp
Variants of these variables with the punctuation followed immediately by
.Ql D
or
.Ql F ,
e.g.\&
.Ql $(@D) ,
are legacy forms equivalent to using the
.Ql :H
and
.Ql :T
modifiers.
These forms are accepted for compatibility with
.At V
makefiles and POSIX but are not recommended.
.Pp
Four of the local variables may be used in sources on dependency lines
because they expand to the proper value for each target on the line.
These variables are
.Sq Va .TARGET ,
.Sq Va .PREFIX ,
.Sq Va .ARCHIVE ,
and
.Sq Va .MEMBER .
.Ss Additional built-in variables
In addition,
.Nm
sets or knows about the following variables:
.Bl -tag
.\" NB: This list is sorted case-insensitive, ignoring punctuation.
.\" NB: To find all built-in variables in make's source code,
.\" NB: search for Var_*, Global_*, SetVarObjdir, GetBooleanExpr,
.\" NB: and the implementation of Var_SetWithFlags.
.\" NB: Last synced on 2023-01-01.
.It Va .ALLTARGETS
The list of all targets encountered in the makefiles.
If evaluated during makefile parsing,
lists only those targets encountered thus far.
.It Va .CURDIR
A path to the directory where
.Nm
was executed.
Refer to the description of
.Sq Va PWD
for more details.
.It Va .ERROR_CMD
Is used in error handling, see
.Va MAKE_PRINT_VAR_ON_ERROR .
.It Va .ERROR_CWD
Is used in error handling, see
.Va MAKE_PRINT_VAR_ON_ERROR .
.It Va .ERROR_META_FILE
Is used in error handling in
.Dq meta
mode, see
.Va MAKE_PRINT_VAR_ON_ERROR .
.It Va .ERROR_TARGET
Is used in error handling, see
.Va MAKE_PRINT_VAR_ON_ERROR .
.It Va .INCLUDEDFROMDIR
The directory of the file this makefile was included from.
.It Va .INCLUDEDFROMFILE
The filename of the file this makefile was included from.
.\" .INCLUDES is intentionally undocumented, as it is obsolete.
.\" .LIBS is intentionally undocumented, as it is obsolete.
.It Va MACHINE
The machine hardware name, see
.Xr uname 1 .
.It Va MACHINE_ARCH
The machine processor architecture name, see
.Xr uname 1 .
.It Va MAKE
The name that
.Nm
was executed with
.Pq Va argv[0] .
.It Va .MAKE
The same as
.Va MAKE ,
for compatibility.
The preferred variable to use is the environment variable
.Ev MAKE
because it is more compatible with other make variants
and cannot be confused with the special target with the same name.
.It Va .MAKE.ALWAYS_PASS_JOB_QUEUE
Tells
.Nm
whether to pass the descriptors of the job token queue
even if the target is not tagged with
.Ic .MAKE
The default is
.Ql Pa yes
for backwards compatability with
.Fx 9.0
and earlier.
.\" '.MAKE.cmd_filtered' is intentionally undocumented,
.\" as it is an internal implementation detail.
.It Va .MAKE.DEPENDFILE
Names the makefile (default
.Sq Pa .depend )
from which generated dependencies are read.
.It Va .MAKE.DIE_QUIETLY
If set to
.Ql true ,
do not print error information at the end.
.It Va .MAKE.EXPAND_VARIABLES
A boolean that controls the default behavior of the
.Fl V
option.
If true, variable values printed with
.Fl V
are fully expanded; if false, the raw variable contents (which may
include additional unexpanded variable references) are shown.
.It Va .MAKE.EXPORTED
The list of variables exported by
.Nm .
.It Va MAKEFILE
The top-level makefile that is currently read,
as given in the command line.
.It Va .MAKEFLAGS
The environment variable
.Sq Ev MAKEFLAGS
may contain anything that
may be specified on
.Nm Ns 's
command line.
Anything specified on
.Nm Ns 's
command line is appended to the
.Va .MAKEFLAGS
variable, which is then added to the environment for all programs that
.Nm
executes.
.It Va .MAKE.GID
The numeric group ID of the user running
.Nm .
It is read-only.
.It Va .MAKE.JOB.PREFIX
If
.Nm
is run with
.Fl j ,
the output for each target is prefixed with a token
.Dl --- Ar target Li ---
the first part of which can be controlled via
.Va .MAKE.JOB.PREFIX .
If
.Va .MAKE.JOB.PREFIX
is empty, no token is printed.
For example, setting
.Va .MAKE.JOB.PREFIX
to
.Ql ${.newline}---${.MAKE:T}[${.MAKE.PID}]
would produce tokens like
.Dl ---make[1234] Ar target Li ---
making it easier to track the degree of parallelism being achieved.
.It Va .MAKE.JOBS
The argument to the
.Fl j
option.
.It Va .MAKE.LEVEL
The recursion depth of
.Nm .
The top-level instance of
.Nm
has level 0, and each child make has its parent level plus 1.
This allows tests like:
.Li .if ${.MAKE.LEVEL} == 0
to protect things which should only be evaluated in the top-level instance of
.Nm .
.It Va .MAKE.LEVEL.ENV
The name of the environment variable that stores the level of nested calls to
.Nm .
.It Va .MAKE.MAKEFILE_PREFERENCE
The ordered list of makefile names
(default
.Sq Pa makefile ,
.Sq Pa Makefile )
that
.Nm
looks for.
.It Va .MAKE.MAKEFILES
The list of makefiles read by
.Nm ,
which is useful for tracking dependencies.
Each makefile is recorded only once, regardless of the number of times read.
.It Va .MAKE.META.BAILIWICK
In
.Dq meta
mode, provides a list of prefixes which
match the directories controlled by
.Nm .
If a file that was generated outside of
.Va .OBJDIR
but within said bailiwick is missing,
the current target is considered out-of-date.
.It Va .MAKE.META.CMP_FILTER
In
.Dq meta
mode, it can (very rarely!) be useful to filter command
lines before comparison.
This variable can be set to a set of modifiers that are applied to
each line of the old and new command that differ, if the filtered
commands still differ, the target is considered out-of-date.
.It Va .MAKE.META.CREATED
In
.Dq meta
mode, this variable contains a list of all the meta files
updated.
If not empty, it can be used to trigger processing of
.Va .MAKE.META.FILES .
.It Va .MAKE.META.FILES
In
.Dq meta
mode, this variable contains a list of all the meta files
used (updated or not).
This list can be used to process the meta files to extract dependency
information.
.It Va .MAKE.META.IGNORE_FILTER
Provides a list of variable modifiers to apply to each pathname.
Ignore if the expansion is an empty string.
.It Va .MAKE.META.IGNORE_PATHS
Provides a list of path prefixes that should be ignored;
because the contents are expected to change over time.
The default list includes:
.Sq Pa /dev /etc /proc /tmp /var/run /var/tmp
.It Va .MAKE.META.IGNORE_PATTERNS
Provides a list of patterns to match against pathnames.
Ignore any that match.
.It Va .MAKE.META.PREFIX
Defines the message printed for each meta file updated in
.Dq meta verbose
mode.
The default value is:
.Dl Building ${.TARGET:H:tA}/${.TARGET:T}
.It Va .MAKE.MODE
Processed after reading all makefiles.
Affects the mode that
.Nm
runs in.
It can contain these keywords:
.Bl -tag -width indent
.It Cm compat
Like
.Fl B ,
puts
.Nm
into
.Dq compat
mode.
.It Cm meta
Puts
.Nm
into
.Dq meta
mode, where meta files are created for each target
to capture the command run, the output generated, and if
.Xr filemon 4
is available, the system calls which are of interest to
.Nm .
The captured output can be useful when diagnosing errors.
.It Cm curdirOk= Ns Ar bf
By default,
.Nm
does not create
.Pa .meta
files in
.Sq Va .CURDIR .
This can be overridden by setting
.Ar bf
to a value which represents true.
.It Cm missing-meta= Ns Ar bf
If
.Ar bf
is true, a missing
.Pa .meta
file makes the target out-of-date.
.It Cm missing-filemon= Ns Ar bf
If
.Ar bf
is true, missing filemon data makes the target out-of-date.
.It Cm nofilemon
Do not use
.Xr filemon 4 .
.It Cm env
For debugging, it can be useful to include the environment
in the
.Pa .meta
file.
.It Cm verbose
If in
.Dq meta
mode, print a clue about the target being built.
This is useful if the build is otherwise running silently.
The message printed is the expanded value of
.Va .MAKE.META.PREFIX .
.It Cm ignore-cmd
Some makefiles have commands which are simply not stable.
This keyword causes them to be ignored for
determining whether a target is out of date in
.Dq meta
mode.
See also
.Ic .NOMETA_CMP .
.It Cm silent= Ns Ar bf
If
.Ar bf
is true, when a .meta file is created, mark the target
.Ic .SILENT .
.It Cm randomize-targets
In both compat and parallel mode, do not make the targets in the usual order,
but instead randomize their order.
This mode can be used to detect undeclared dependencies between files.
.El
.It Va MAKEOBJDIR
Used to create files in a separate directory, see
.Va .OBJDIR .
.It Va MAKE_OBJDIR_CHECK_WRITABLE
Used to force a separate directory for the created files,
even if that directory is not writable, see
.Va .OBJDIR .
.It Va MAKEOBJDIRPREFIX
Used to create files in a separate directory, see
.Va .OBJDIR .
.It Va .MAKE.OS
The name of the operating system, see
.Xr uname 1 .
It is read-only.
.It Va .MAKEOVERRIDES
This variable is used to record the names of variables assigned to
on the command line, so that they may be exported as part of
.Sq Ev MAKEFLAGS .
This behavior can be disabled by assigning an empty value to
.Sq Va .MAKEOVERRIDES
within a makefile.
Extra variables can be exported from a makefile
by appending their names to
.Sq Va .MAKEOVERRIDES .
.Sq Ev MAKEFLAGS
is re-exported whenever
.Sq Va .MAKEOVERRIDES
is modified.
.It Va .MAKE.PATH_FILEMON
If
.Nm
was built with
.Xr filemon 4
support, this is set to the path of the device node.
This allows makefiles to test for this support.
.It Va .MAKE.PID
The process ID of
.Nm .
It is read-only.
.It Va .MAKE.PPID
The parent process ID of
.Nm .
It is read-only.
.It Va MAKE_PRINT_VAR_ON_ERROR
When
.Nm
stops due to an error, it sets
.Sq Va .ERROR_TARGET
to the name of the target that failed,
.Sq Va .ERROR_CMD
to the commands of the failed target,
and in
.Dq meta
mode, it also sets
.Sq Va .ERROR_CWD
to the
.Xr getcwd 3 ,
and
.Sq Va .ERROR_META_FILE
to the path of the meta file (if any) describing the failed target.
It then prints its name and the value of
.Sq Va .CURDIR
as well as the value of any variables named in
.Sq Va MAKE_PRINT_VAR_ON_ERROR .
.It Va .MAKE.SAVE_DOLLARS
If true,
.Ql $$
are preserved when doing
.Ql :=
assignments.
The default is false, for backwards compatibility.
Set to true for compatability with other makes.
If set to false,
.Ql $$
becomes
.Ql $
per normal evaluation rules.
.It Va .MAKE.TARGET_LOCAL_VARIABLES
If set to
.Ql false ,
apparent variable assignments in dependency lines are
treated as normal sources.
.It Va .MAKE.UID
The numeric ID of the user running
.Nm .
It is read-only.
.\" 'MAKE_VERSION' is intentionally undocumented
.\" since it is only defined in the bmake distribution,
.\" but not in NetBSD's native make.
.\" '.meta.%d.lcwd' is intentionally undocumented
.\" since it is an internal implementation detail.
.\" '.meta.%d.ldir' is intentionally undocumented
.\" since it is an internal implementation detail.
.\" 'MFLAGS' is intentionally undocumented
.\" since it is obsolete.
.It Va .newline
This variable is simply assigned a newline character as its value.
It is read-only.
This allows expansions using the
.Cm \&:@
modifier to put a newline between
iterations of the loop rather than a space.
For example, in case of an error,
.Nm
prints the variable names and their values using:
.Dl ${MAKE_PRINT_VAR_ON_ERROR:@v@$v='${$v}'${.newline}@}
.It Va .OBJDIR
A path to the directory where the targets are built.
Its value is determined by trying to
.Xr chdir 2
to the following directories in order and using the first match:
.Bl -enum
.It
.Cm ${MAKEOBJDIRPREFIX} Ns Cm ${.CURDIR}
.Pp
(Only if
.Sq Ev MAKEOBJDIRPREFIX
is set in the environment or on the command line.)
.It
.Cm ${MAKEOBJDIR}
.Pp
(Only if
.Sq Ev MAKEOBJDIR
is set in the environment or on the command line.)
.It
.Cm ${.CURDIR} Ns Pa /obj. Ns Cm ${MACHINE}
.It
.Cm ${.CURDIR} Ns Pa /obj
.It
.Pa /usr/obj/ Ns Cm ${.CURDIR}
.It
.Cm ${.CURDIR}
.El
.Pp
Variable expansion is performed on the value before it is used,
so expressions such as
.Cm ${.CURDIR:S,^/usr/src,/var/obj,}
may be used.
This is especially useful with
.Sq Ev MAKEOBJDIR .
.Pp
.Sq Va .OBJDIR
may be modified in the makefile via the special target
.Sq Ic .OBJDIR .
In all cases,
.Nm
changes to the specified directory if it exists, and sets
.Sq Va .OBJDIR
and
.Sq Va PWD
to that directory before executing any targets.
.Pp
Except in the case of an explicit
.Sq Ic .OBJDIR
target,
.Nm
checks that the specified directory is writable and ignores it if not.
This check can be skipped by setting the environment variable
.Sq Ev MAKE_OBJDIR_CHECK_WRITABLE
to
.Dq no .
.It Va .PARSEDIR
The directory name of the current makefile being parsed.
.It Va .PARSEFILE
The basename of the current makefile being parsed.
This variable and
.Sq Va .PARSEDIR
are both set only while the makefiles are being parsed.
To retain their current values,
assign them to a variable using assignment with expansion
.Sq Cm \&:= .
.It Va .PATH
The space-separated list of directories that
.Nm
searches for files.
To update this search list, use the special target
.Sq Ic .PATH
rather than modifying the variable directly.
.It Va %POSIX
Is set in POSIX mode, see the special
.Ql Va .POSIX
target.
.\" XXX: There is no make variable named 'PWD',
.\" XXX: make only reads and writes the environment variable 'PWD'.
.It Va PWD
Alternate path to the current directory.
.Nm
normally sets
.Sq Va .CURDIR
to the canonical path given by
.Xr getcwd 3 .
However, if the environment variable
.Sq Ev PWD
is set and gives a path to the current directory,
.Nm
sets
.Sq Va .CURDIR
to the value of
.Sq Ev PWD
instead.
This behavior is disabled if
.Sq Ev MAKEOBJDIRPREFIX
is set or
.Sq Ev MAKEOBJDIR
contains a variable transform.
.Sq Va PWD
is set to the value of
.Sq Va .OBJDIR
for all programs which
.Nm
executes.
.It Va .SHELL
The pathname of the shell used to run target scripts.
It is read-only.
.It Va .SUFFIXES
The list of known suffixes.
It is read-only.
.It Va .SYSPATH
The space-separated list of directories that
.Nm
searches for makefiles, referred to as the system include path.
To update this search list, use the special target
.Sq Ic .SYSPATH
rather than modifying the variable which is read-only.
.It Va .TARGETS
The list of targets explicitly specified on the command line, if any.
.It Va VPATH
The colon-separated
.Pq Dq \&:
list of directories that
.Nm
searches for files.
This variable is supported for compatibility with old make programs only, use
.Sq Va .PATH
instead.
.El
.Ss Variable modifiers
The general format of a variable expansion is:
.Pp
.Sm off
.D1 Ic \&${ Ar variable\| Oo Ic \&: Ar modifier\| Oo Ic \&: No ... Oc Oc Ic \&}
.Sm on
.Pp
Each modifier begins with a colon.
To escape a colon, precede it with a backslash
.Ql \e .
.Pp
A list of indirect modifiers can be specified via a variable, as follows:
.Pp
.Bd -literal -offset indent
.Ar modifier_variable\^ Li \&= Ar modifier Ns Oo Ic \&: Ns No ... Oc

.Sm off
.Ic \&${ Ar variable Ic \&:${ Ar modifier_variable Ic \&} Oo Ic \&: No ... Oc Ic \&}
.Sm on
.Ed
.Pp
In this case, the first modifier in the
.Ar modifier_variable
does not start with a colon,
since that colon already occurs in the referencing variable.
If any of the modifiers in the
.Ar modifier_variable
contains a dollar sign
.Pq Ql $ ,
these must be doubled to avoid early expansion.
.Pp
Some modifiers interpret the expression value as a single string,
others treat the expression value as a whitespace-separated list of words.
When splitting a string into words,
whitespace can be escaped using double quotes, single quotes and backslashes,
like in the shell.
The quotes and backslashes are retained in the words.
.Pp
The supported modifiers are:
.Bl -tag -width EEE
.It Cm \&:E
Replaces each word with its suffix.
.It Cm \&:H
Replaces each word with its dirname.
.It Cm \&:M\| Ns Ar pattern
Selects only those words that match
.Ar pattern .
The standard shell wildcard characters
.Pf ( Ql * ,
.Ql \&? ,
and
.Ql \&[] )
may
be used.
The wildcard characters may be escaped with a backslash
.Pq Ql \e .
As a consequence of the way values are split into words, matched,
and then joined, the construct
.Ql ${VAR:M*}
removes all leading and trailing whitespace
and normalizes the inter-word spacing to a single space.
.It Cm \&:N\| Ns Ar pattern
This is the opposite of
.Sq Cm \&:M ,
selecting all words which do
.Em not
match
.Ar pattern .
.It Cm \&:O
Orders the words lexicographically.
.It Cm \&:On
Orders the words numerically.
A number followed by one of
.Ql k ,
.Ql M
or
.Ql G
is multiplied by the appropriate factor, which is 1024 for
.Ql k ,
1048576 for
.Ql M ,
or 1073741824 for
.Ql G .
Both upper- and lower-case letters are accepted.
.It Cm \&:Or
Orders the words in reverse lexicographical order.
.It Cm \&:Orn
Orders the words in reverse numerical order.
.It Cm \&:Ox
Shuffles the words.
The results are different each time you are referring to the
modified variable; use the assignment with expansion
.Sq Cm \&:=
to prevent such behavior.
For example,
.Bd -literal -offset indent
LIST=			uno due tre quattro
RANDOM_LIST=		${LIST:Ox}
STATIC_RANDOM_LIST:=	${LIST:Ox}

all:
	@echo "${RANDOM_LIST}"
	@echo "${RANDOM_LIST}"
	@echo "${STATIC_RANDOM_LIST}"
	@echo "${STATIC_RANDOM_LIST}"
.Ed
may produce output similar to:
.Bd -literal -offset indent
quattro due tre uno
tre due quattro uno
due uno quattro tre
due uno quattro tre
.Ed
.It Cm \&:Q
Quotes every shell meta-character in the value, so that it can be passed
safely to the shell.
.It Cm \&:q
Quotes every shell meta-character in the value, and also doubles
.Sq $
characters so that it can be passed
safely through recursive invocations of
.Nm .
This is equivalent to
.Sq Cm \&:S/\e\&$/&&/g:Q .
.It Cm \&:R
Replaces each word with everything but its suffix.
.It Cm \&:range Ns Oo Cm = Ns Ar count Oc
The value is an integer sequence representing the words of the original
value, or the supplied
.Ar count .
.It Cm \&:gmtime Ns Oo Cm = Ns Ar timestamp Oc
The value is interpreted as a format string for
.Xr strftime 3 ,
using
.Xr gmtime 3 ,
producing the formatted timestamp.
If a
.Ar timestamp
value is not provided or is 0, the current time is used.
.It Cm \&:hash
Computes a 32-bit hash of the value and encodes it as 8 hex digits.
.It Cm \&:localtime Ns Oo Cm = Ns Ar timestamp Oc
The value is interpreted as a format string for
.Xr strftime 3 ,
using
.Xr localtime 3 ,
producing the formatted timestamp.
If a
.Ar timestamp
value is not provided or is 0, the current time is used.
.It Cm \&:mtime Ns Oo Cm = Ns Ar timestamp Oc
Call
.Xr stat 2
with each word as pathname;
use
.Ql st_mtime
as the new value.
If
.Xr stat 2
fails; use
.Ar timestamp
or current time.
If
.Ar timestamp
is set to
.Ql error ,
then
.Xr stat 2
failure will cause an error.
.It Cm \&:tA
Attempts to convert the value to an absolute path using
.Xr realpath 3 .
If that fails, the value is unchanged.
.It Cm \&:tl
Converts the value to lower-case letters.
.It Cm \&:ts Ns Ar c
When joining the words after a modifier that treats the value as words,
the words are normally separated by a space.
This modifier changes the separator to the character
.Ar c .
If
.Ar c
is omitted, no separator is used.
The common escapes (including octal numeric codes) work as expected.
.It Cm \&:tu
Converts the value to upper-case letters.
.It Cm \&:tW
Causes subsequent modifiers to treat the value as a single word
(possibly containing embedded whitespace).
See also
.Sq Cm \&:[*] .
.It Cm \&:tw
Causes the value to be treated as a list of words.
See also
.Sq Cm \&:[@] .
.Sm off
.It Cm \&:S\| No \&/ Ar old_string\| No \&/ Ar new_string\| No \&/ Op Cm 1gW
.Sm on
Modifies the first occurrence of
.Ar old_string
in each word of the value, replacing it with
.Ar new_string .
If a
.Ql g
is appended to the last delimiter of the pattern,
all occurrences in each word are replaced.
If a
.Ql 1
is appended to the last delimiter of the pattern,
only the first occurrence is affected.
If a
.Ql W
is appended to the last delimiter of the pattern,
the value is treated as a single word.
If
.Ar old_string
begins with a caret
.Pq Ql ^ ,
.Ar old_string
is anchored at the beginning of each word.
If
.Ar old_string
ends with a dollar sign
.Pq Ql \&$ ,
it is anchored at the end of each word.
Inside
.Ar new_string ,
an ampersand
.Pq Ql &
is replaced by
.Ar old_string
(without the anchoring
.Ql ^
or
.Ql \&$ ) .
Any character may be used as the delimiter for the parts of the modifier
string.
The anchoring, ampersand and delimiter characters can be escaped with a
backslash
.Pq Ql \e .
.Pp
Both
.Ar old_string
and
.Ar new_string
may contain nested expressions.
To prevent a dollar sign from starting a nested expression,
escape it with a backslash.
.Sm off
.It Cm \&:C\| No \&/ Ar pattern\| No \&/ Ar replacement\| No \&/ Op Cm 1gW
.Sm on
The
.Cm \&:C
modifier works like the
.Cm \&:S
modifier except that the old and new strings, instead of being
simple strings, are an extended regular expression
.Ar pattern
(see
.Xr regex 3 )
and an
.Xr ed 1 Ns \-style
.Ar replacement .
Normally, the first occurrence of the pattern
.Ar pattern
in each word of the value is substituted with
.Ar replacement .
The
.Ql 1
modifier causes the substitution to apply to at most one word; the
.Ql g
modifier causes the substitution to apply to as many instances of the
search pattern
.Ar pattern
as occur in the word or words it is found in; the
.Ql W
modifier causes the value to be treated as a single word
(possibly containing embedded whitespace).
.Pp
As for the
.Cm \&:S
modifier, the
.Ar pattern
and
.Ar replacement
are subjected to variable expansion before being parsed as
regular expressions.
.It Cm \&:T
Replaces each word with its last path component (basename).
.It Cm \&:u
Removes adjacent duplicate words (like
.Xr uniq 1 ) .
.Sm off
.It Cm \&:\&?\| Ar true_string\| Cm \&: Ar false_string
.Sm on
If the variable name (not its value), when parsed as a
.Cm .if
conditional expression, evaluates to true, return as its value the
.Ar true_string ,
otherwise return the
.Ar false_string .
Since the variable name is used as the expression,
\&:\&? must be the first modifier after the variable name
.No itself Ns \^\(em\^ Ns
which, of course, usually contains variable expansions.
A common error is trying to use expressions like
.Dl ${NUMBERS:M42:?match:no}
which actually tests defined(NUMBERS).
To determine if any words match
.Dq 42 ,
you need to use something like:
.Dl ${"${NUMBERS:M42}" != \&"\&":?match:no} .
.It Cm :\| Ns Ar old_string\| Ns Cm = Ns Ar new_string
This is the
.At V
style substitution.
It can only be the last modifier specified,
as a
.Ql \&:
in either
.Ar old_string
or
.Ar new_string
is treated as a regular character, not as the end of the modifier.
.Pp
If
.Ar old_string
does not contain the pattern matching character
.Ql % ,
and the word ends with
.Ar old_string
or equals it,
that suffix is replaced with
.Ar new_string .
.Pp
Otherwise, the first
.Ql %
in
.Ar old_string
matches a possibly empty substring of arbitrary characters,
and if the whole pattern is found in the word,
the matching part is replaced with
.Ar new_string ,
and the first occurrence of
.Ql %
in
.Ar new_string
(if any) is replaced with the substring matched by the
.Ql % .
.Pp
Both
.Ar old_string
and
.Ar new_string
may contain nested expressions.
To prevent a dollar sign from starting a nested expression,
escape it with a backslash.
.Sm off
.It Cm \&:@ Ar varname\| Cm @ Ar string\| Cm @
.Sm on
This is the loop expansion mechanism from the OSF Development
Environment (ODE) make.
Unlike
.Cm \&.for
loops, expansion occurs at the time of reference.
For each word in the value, assign the word to the variable named
.Ar varname
and evaluate
.Ar string .
The ODE convention is that
.Ar varname
should start and end with a period, for example:
.Dl ${LINKS:@.LINK.@${LN} ${TARGET} ${.LINK.}@}
.Pp
However, a single-letter variable is often more readable:
.Dl ${MAKE_PRINT_VAR_ON_ERROR:@v@$v='${$v}'${.newline}@}
.It Cm \&:_ Ns Oo Cm = Ns Ar var Oc
Saves the current variable value in
.Ql $_
or the named
.Ar var
for later reference.
Example usage:
.Bd -literal -offset indent
M_cmpv.units = 1 1000 1000000
M_cmpv = S,., ,g:_:range:@i@+ $${_:[-$$i]} \&\\
\\* $${M_cmpv.units:[$$i]}@:S,^,expr 0 ,1:sh

.Dv .if ${VERSION:${M_cmpv}} < ${3.1.12:L:${M_cmpv}}

.Ed
Here
.Ql $_
is used to save the result of the
.Ql :S
modifier which is later referenced using the index values from
.Ql :range .
.It Cm \&:U\| Ns Ar newval
If the variable is undefined,
.Ar newval
is the value.
If the variable is defined, the existing value is returned.
This is another ODE make feature.
It is handy for setting per-target CFLAGS for instance:
.Dl ${_${.TARGET:T}_CFLAGS:U${DEF_CFLAGS}}
If a value is only required if the variable is undefined, use:
.Dl ${VAR:D:Unewval}
.It Cm \&:D\| Ns Ar newval
If the variable is defined,
.Ar newval
is the value.
.It Cm \&:L
The name of the variable is the value.
.It Cm \&:P
The path of the node which has the same name as the variable is the value.
If no such node exists or its path is null, the name of the variable is used.
In order for this modifier to work, the name (node) must at least have
appeared on the right-hand side of a dependency.
.Sm off
.It Cm \&:\&! Ar cmd\| Cm \&!
.Sm on
The output of running
.Ar cmd
is the value.
.It Cm \&:sh
The value is run as a command, and the output becomes the new value.
.It Cm \&::= Ns Ar str
The variable is assigned the value
.Ar str
after substitution.
This modifier and its variations are useful in obscure situations
such as wanting to set a variable
at a point where a target's shell commands are being parsed.
These assignment modifiers always expand to nothing.
.Pp
The
.Sq Cm \&::
helps avoid false matches with the
.At V
style
.Ql \&:=
modifier and since substitution always occurs, the
.Ql \&::=
form is vaguely appropriate.
.It Cm \&::?= Ns Ar str
As for
.Cm \&::=
but only if the variable does not already have a value.
.It Cm \&::+= Ns Ar str
Append
.Ar str
to the variable.
.It Cm \&::!= Ns Ar cmd
Assign the output of
.Ar cmd
to the variable.
.It Cm \&:\&[ Ns Ar range Ns Cm \&]
Selects one or more words from the value,
or performs other operations related to the way in which the
value is split into words.
.Pp
An empty value, or a value that consists entirely of white-space,
is treated as a single word.
For the purposes of the
.Sq Cm \&:[]
modifier, the words are indexed both forwards using positive integers
(where index 1 represents the first word),
and backwards using negative integers
(where index \-1 represents the last word).
.Pp
The
.Ar range
is subjected to variable expansion, and the expanded result is
then interpreted as follows:
.Bl -tag -width index
.\" :[n]
.It Ar index
Selects a single word from the value.
.\" :[start..end]
.It Ar start Ns Cm \&.. Ns Ar end
Selects all words from
.Ar start
to
.Ar end ,
inclusive.
For example,
.Sq Cm \&:[2..-1]
selects all words from the second word to the last word.
If
.Ar start
is greater than
.Ar end ,
the words are output in reverse order.
For example,
.Sq Cm \&:[-1..1]
selects all the words from last to first.
If the list is already ordered,
this effectively reverses the list,
but it is more efficient to use
.Sq Cm \&:Or
instead of
.Sq Cm \&:O:[-1..1] .
.\" :[*]
.It Cm \&*
Causes subsequent modifiers to treat the value as a single word
(possibly containing embedded whitespace).
Analogous to the effect of
.Li \&$*
in Bourne shell.
.\" :[0]
.It 0
Means the same as
.Sq Cm \&:[*] .
.\" :[*]
.It Cm \&@
Causes subsequent modifiers to treat the value as a sequence of words
delimited by whitespace.
Analogous to the effect of
.Li \&$@
in Bourne shell.
.\" :[#]
.It Cm \&#
Returns the number of words in the value.
.El \" :[range]
.El
.Sh DIRECTIVES
.Nm
offers directives for including makefiles, conditionals and for loops.
All these directives are identified by a line beginning with a single dot
.Pq Ql \&.
character, followed by the keyword of the directive, such as
.Cm include
or
.Cm if .
.Ss File inclusion
Files are included with either
.Cm \&.include \&< Ns Ar file Ns Cm \&>
or
.Cm \&.include \&\*q Ns Ar file Ns Cm \&\*q .
Variables between the angle brackets or double quotes are expanded
to form the file name.
If angle brackets are used, the included makefile is expected to be in
the system makefile directory.
If double quotes are used, the including makefile's directory and any
directories specified using the
.Fl I
option are searched before the system makefile directory.
.Pp
For compatibility with other make variants,
.Sq Cm include Ar file No ...
(without leading dot)
is also accepted.
.Pp
If the include statement is written as
.Cm .-include
or as
.Cm .sinclude ,
errors locating and/or opening include files are ignored.
.Pp
If the include statement is written as
.Cm .dinclude ,
not only are errors locating and/or opening include files ignored,
but stale dependencies within the included file are ignored just like in
.Va .MAKE.DEPENDFILE .
.Ss Exporting variables
The directives for exporting and unexporting variables are:
.Bl -tag -width Ds
.It Ic .export Ar variable No ...
Export the specified global variable.
If no variable list is provided, all globals are exported
except for internal variables (those that start with
.Ql \&. ) .
This is not affected by the
.Fl X
flag, so should be used with caution.
For compatibility with other make programs,
.Cm export Ar variable\| Ns Cm \&= Ns Ar value
(without leading dot) is also accepted.
.Pp
Appending a variable name to
.Va .MAKE.EXPORTED
is equivalent to exporting a variable.
.It Ic .export-env Ar variable No ...
The same as
.Ql .export ,
except that the variable is not appended to
.Va .MAKE.EXPORTED .
This allows exporting a value to the environment which is different from that
used by
.Nm
internally.
.It Ic .export-literal Ar variable No ...
The same as
.Ql .export-env ,
except that variables in the value are not expanded.
.It Ic .unexport Ar variable No ...
The opposite of
.Ql .export .
The specified global
.Ar variable
is removed from
.Va .MAKE.EXPORTED .
If no variable list is provided, all globals are unexported,
and
.Va .MAKE.EXPORTED
deleted.
.It Ic .unexport-env
Unexport all globals previously exported and
clear the environment inherited from the parent.
This operation causes a memory leak of the original environment,
so should be used sparingly.
Testing for
.Va .MAKE.LEVEL
being 0 would make sense.
Also note that any variables which originated in the parent environment
should be explicitly preserved if desired.
For example:
.Bd -literal -offset indent
.Li .if ${.MAKE.LEVEL} == 0
PATH := ${PATH}
.Li .unexport-env
.Li .export PATH
.Li .endif
.Pp
.Ed
Would result in an environment containing only
.Sq Ev PATH ,
which is the minimal useful environment.
.\" TODO: Check the below sentence, environment variables don't start with '.'.
Actually
.Sq Va .MAKE.LEVEL
is also pushed into the new environment.
.El
.Ss Messages
The directives for printing messages to the output are:
.Bl -tag -width Ds
.It Ic .info Ar message
The message is printed along with the name of the makefile and line number.
.It Ic .warning Ar message
The message prefixed by
.Sq Li warning:
is printed along with the name of the makefile and line number.
.It Ic .error Ar message
The message is printed along with the name of the makefile and line number,
.Nm
exits immediately.
.El
.Ss Conditionals
The directives for conditionals are:
.ds maybenot Oo Ic \&! Oc Ns
.Bl -tag
.It Ic .if \*[maybenot] Ar expression Op Ar operator expression No ...
Test the value of an expression.
.It Ic .ifdef \*[maybenot] Ar variable Op Ar operator variable No ...
Test whether a variable is defined.
.It Ic .ifndef \*[maybenot] Ar variable Op Ar operator variable No ...
Test whether a variable is not defined.
.It Ic .ifmake \*[maybenot] Ar target Op Ar operator target No ...
Test the target being requested.
.It Ic .ifnmake \*[maybenot] Ar target Op Ar operator target No ...
Test the target being requested.
.It Ic .else
Reverse the sense of the last conditional.
.It Ic .elif \*[maybenot] Ar expression Op Ar operator expression No ...
A combination of
.Sq Ic .else
followed by
.Sq Ic .if .
.It Ic .elifdef \*[maybenot] Ar variable Op Ar operator variable No ...
A combination of
.Sq Ic .else
followed by
.Sq Ic .ifdef .
.It Ic .elifndef \*[maybenot] Ar variable Op Ar operator variable No ...
A combination of
.Sq Ic .else
followed by
.Sq Ic .ifndef .
.It Ic .elifmake \*[maybenot] Ar target Op Ar operator target No ...
A combination of
.Sq Ic .else
followed by
.Sq Ic .ifmake .
.It Ic .elifnmake \*[maybenot] Ar target Op Ar operator target No ...
A combination of
.Sq Ic .else
followed by
.Sq Ic .ifnmake .
.It Ic .endif
End the body of the conditional.
.El
.Pp
The
.Ar operator
may be any one of the following:
.Bl -tag
.It Ic \&|\&|
Logical OR.
.It Ic \&&&
Logical AND; of higher precedence than
.Sq Ic \&|\&| .
.El
.Pp
.Nm
only evaluates a conditional as far as is necessary to determine its value.
Parentheses can be used to override the operator precedence.
The boolean operator
.Sq Ic \&!
may be used to logically negate an entire conditional.
It is of higher precedence than
.Sq Ic \&&& .
.Pp
The value of
.Ar expression
may be any of the following function call expressions:
.Bl -tag
.Sm off
.It Ic defined Li \&( Ar varname Li \&)
.Sm on
Evaluates to true if the variable
.Ar varname
has been defined.
.Sm off
.It Ic make Li \&( Ar target Li \&)
.Sm on
Evaluates to true if the target was specified as part of
.Nm Ns 's
command line or was declared the default target (either implicitly or
explicitly, see
.Va .MAIN )
before the line containing the conditional.
.Sm off
.It Ic empty Li \&( Ar varname Oo Li : Ar modifiers Oc Li \&)
.Sm on
Evaluates to true if the expansion of the variable,
after applying the modifiers, results in an empty string.
.Sm off
.It Ic exists Li \&( Ar pathname Li \&)
.Sm on
Evaluates to true if the given pathname exists.
If relative, the pathname is searched for on the system search path (see
.Va .PATH ) .
.Sm off
.It Ic target Li \&( Ar target Li \&)
.Sm on
Evaluates to true if the target has been defined.
.Sm off
.It Ic commands Li \&( Ar target Li \&)
.Sm on
Evaluates to true if the target has been defined
and has commands associated with it.
.El
.Pp
.Ar Expression
may also be an arithmetic or string comparison.
Variable expansion is performed on both sides of the comparison.
If both sides are numeric and neither is enclosed in quotes,
the comparison is done numerically, otherwise lexicographically.
A string is interpreted as hexadecimal integer if it is preceded by
.Li 0x ,
otherwise it is a decimal floating-point number;
octal numbers are not supported.
.Pp
All comparisons may use the operators
.Sq Ic \&==
and
.Sq Ic \&!= .
Numeric comparisons may also use the operators
.Sq Ic \&< ,
.Sq Ic \&<= ,
.Sq Ic \&>
and
.Sq Ic \&>= .
.Pp
If the comparison has neither a comparison operator nor a right side,
the expression evaluates to true if it is nonempty
and its numeric value (if any) is not zero.
.Pp
When
.Nm
is evaluating one of these conditional expressions, and it encounters
a (whitespace separated) word it doesn't recognize, either the
.Dq make
or
.Dq defined
function is applied to it, depending on the form of the conditional.
If the form is
.Sq Ic .ifdef ,
.Sq Ic .ifndef
or
.Sq Ic .if ,
the
.Dq defined
function is applied.
Similarly, if the form is
.Sq Ic .ifmake
or
.Sq Ic .ifnmake ,
the
.Dq make
function is applied.
.Pp
If the conditional evaluates to true,
parsing of the makefile continues as before.
If it evaluates to false, the following lines are skipped.
In both cases, this continues until the corresponding
.Sq Ic .else
or
.Sq Ic .endif
is found.
.Ss For loops
For loops are typically used to apply a set of rules to a list of files.
The syntax of a for loop is:
.Pp
.Bl -tag -compact -width Ds
.It Ic \&.for Ar variable Oo Ar variable No ... Oc Ic in Ar expression
.It Aq Ar make-lines
.It Ic \&.endfor
.El
.Pp
The
.Ar expression
is expanded and then split into words.
On each iteration of the loop, one word is taken and assigned to each
.Ar variable ,
in order, and these
.Ar variables
are substituted into the
.Ar make-lines
inside the body of the for loop.
The number of words must come out even; that is, if there are three
iteration variables, the number of words provided must be a multiple
of three.
.Pp
If
.Sq Ic .break
is encountered within a
.Cm \&.for
loop, it causes early termination of the loop, otherwise a parse error.
.\" TODO: Describe limitations with defined/empty.
.Ss Other directives
.Bl -tag -width Ds
.It Ic .undef Ar variable No ...
Un-define the specified global variables.
Only global variables can be un-defined.
.El
.Sh COMMENTS
Comments begin with a hash
.Pq Ql \&#
character, anywhere but in a shell
command line, and continue to the end of an unescaped new line.
.Sh SPECIAL SOURCES (ATTRIBUTES)
.Bl -tag -width .IGNOREx
.It Ic .EXEC
Target is never out of date, but always execute commands anyway.
.It Ic .IGNORE
Ignore any errors from the commands associated with this target, exactly
as if they all were preceded by a dash
.Pq Ql \- .
.\" .It Ic .INVISIBLE
.\" XXX
.\" .It Ic .JOIN
.\" XXX
.It Ic .MADE
Mark all sources of this target as being up to date.
.It Ic .MAKE
Execute the commands associated with this target even if the
.Fl n
or
.Fl t
options were specified.
Normally used to mark recursive
.Nm Ns s .
.It Ic .META
Create a meta file for the target, even if it is flagged as
.Ic .PHONY ,
.Ic .MAKE ,
or
.Ic .SPECIAL .
Usage in conjunction with
.Ic .MAKE
is the most likely case.
In
.Dq meta
mode, the target is out-of-date if the meta file is missing.
.It Ic .NOMETA
Do not create a meta file for the target.
Meta files are also not created for
.Ic .PHONY ,
.Ic .MAKE ,
or
.Ic .SPECIAL
targets.
.It Ic .NOMETA_CMP
Ignore differences in commands when deciding if target is out of date.
This is useful if the command contains a value which always changes.
If the number of commands change, though,
the target is still considered out of date.
The same effect applies to any command line that uses the variable
.Va .OODATE ,
which can be used for that purpose even when not otherwise needed or desired:
.Bd -literal -offset indent

skip-compare-for-some:
	@echo this is compared
	@echo this is not ${.OODATE:M.NOMETA_CMP}
	@echo this is also compared

.Ed
The
.Cm \&:M
pattern suppresses any expansion of the unwanted variable.
.It Ic .NOPATH
Do not search for the target in the directories specified by
.Va .PATH .
.It Ic .NOTMAIN
Normally
.Nm
selects the first target it encounters as the default target to be built
if no target was specified.
This source prevents this target from being selected.
.It Ic .OPTIONAL
If a target is marked with this attribute and
.Nm
can't figure out how to create it, it ignores this fact and assumes
the file isn't needed or already exists.
.It Ic .PHONY
The target does not correspond to an actual file;
it is always considered to be out of date,
and is not created with the
.Fl t
option.
Suffix-transformation rules are not applied to
.Ic .PHONY
targets.
.It Ic .PRECIOUS
When
.Nm
is interrupted, it normally removes any partially made targets.
This source prevents the target from being removed.
.It Ic .RECURSIVE
Synonym for
.Ic .MAKE .
.It Ic .SILENT
Do not echo any of the commands associated with this target, exactly
as if they all were preceded by an at sign
.Pq Ql @ .
.It Ic .USE
Turn the target into
.Nm Ns 's
version of a macro.
When the target is used as a source for another target, the other target
acquires the commands, sources, and attributes (except for
.Ic .USE )
of the
source.
If the target already has commands, the
.Ic .USE
target's commands are appended
to them.
.It Ic .USEBEFORE
Like
.Ic .USE ,
but instead of appending, prepend the
.Ic .USEBEFORE
target commands to the target.
.It Ic .WAIT
If
.Ic .WAIT
appears in a dependency line, the sources that precede it are
made before the sources that succeed it in the line.
Since the dependents of files are not made until the file itself
could be made, this also stops the dependents being built unless they
are needed for another branch of the dependency tree.
So given:
.Bd -literal
x: a .WAIT b
	echo x
a:
	echo a
b: b1
	echo b
b1:
	echo b1

.Ed
the output is always
.Ql a ,
.Ql b1 ,
.Ql b ,
.Ql x .
.Pp
The ordering imposed by
.Ic .WAIT
is only relevant for parallel makes.
.El
.Sh SPECIAL TARGETS
Special targets may not be included with other targets, i.e. they must be
the only target specified.
.Bl -tag -width .BEGINx
.It Ic .BEGIN
Any command lines attached to this target are executed before anything
else is done.
.It Ic .DEFAULT
This is sort of a
.Ic .USE
rule for any target (that was used only as a source) that
.Nm
can't figure out any other way to create.
Only the shell script is used.
The
.Va .IMPSRC
variable of a target that inherits
.Ic .DEFAULT Ns 's
commands is set to the target's own name.
.It Ic .DELETE_ON_ERROR
If this target is present in the makefile, it globally causes make to
delete targets whose commands fail.
(By default, only targets whose commands are interrupted during
execution are deleted.
This is the historical behavior.)
This setting can be used to help prevent half-finished or malformed
targets from being left around and corrupting future rebuilds.
.It Ic .END
Any command lines attached to this target are executed after everything
else is done successfully.
.It Ic .ERROR
Any command lines attached to this target are executed when another target fails.
The
.Va .ERROR_TARGET
variable is set to the target that failed.
See also
.Va MAKE_PRINT_VAR_ON_ERROR .
.It Ic .IGNORE
Mark each of the sources with the
.Ic .IGNORE
attribute.
If no sources are specified, this is the equivalent of specifying the
.Fl i
option.
.It Ic .INTERRUPT
If
.Nm
is interrupted, the commands for this target are executed.
.It Ic .MAIN
If no target is specified when
.Nm
is invoked, this target is built.
.It Ic .MAKEFLAGS
This target provides a way to specify flags for
.Nm
at the time when the makefiles are read.
The flags are as if typed to the shell, though the
.Fl f
option has
no effect.
.\" XXX: NOT YET!!!!
.\" .It Ic .NOTPARALLEL
.\" The named targets are executed in non parallel mode.
.\" If no targets are
.\" specified, all targets are executed in non parallel mode.
.It Ic .NOPATH
Apply the
.Ic .NOPATH
attribute to any specified sources.
.It Ic .NOTPARALLEL
Disable parallel mode.
.It Ic .NO_PARALLEL
Synonym for
.Ic .NOTPARALLEL ,
for compatibility with other pmake variants.
.It Ic .NOREADONLY
clear the read-only attribute from the global variables specified as sources.
.It Ic .OBJDIR
The source is a new value for
.Sq Va .OBJDIR .
If it exists,
.Nm
changes the current working directory to it and updates the value of
.Sq Va .OBJDIR .
.It Ic .ORDER
In parallel mode, the named targets are made in sequence.
This ordering does not add targets to the list of targets to be made.
.Pp
Since the dependents of a target do not get built until the target itself
could be built, unless
.Ql a
is built by another part of the dependency graph,
the following is a dependency loop:
.Bd -literal
\&.ORDER: b a
b: a
.Ed
.Pp
.\" XXX: NOT YET!!!!
.\" .It Ic .PARALLEL
.\" The named targets are executed in parallel mode.
.\" If no targets are
.\" specified, all targets are executed in parallel mode.
.It Ic .PATH
The sources are directories which are to be searched for files not
found in the current directory.
If no sources are specified,
any previously specified directories are removed from the search path.
If the source is the special
.Ic .DOTLAST
target, the current working directory is searched last.
.It Ic .PATH. Ns Ar suffix
Like
.Ic .PATH
but applies only to files with a particular suffix.
The suffix must have been previously declared with
.Ic .SUFFIXES .
.It Ic .PHONY
Apply the
.Ic .PHONY
attribute to any specified sources.
.It Ic .POSIX
If this is the first non-comment line in the main makefile,
the variable
.Va %POSIX
is set to the value
.Ql 1003.2
and the makefile
.Ql <posix.mk>
is included if it exists,
to provide POSIX-compatible default rules.
If
.Nm
is run with the
.Fl r
flag, only
.Ql posix.mk
contributes to the default rules.
.It Ic .PRECIOUS
Apply the
.Ic .PRECIOUS
attribute to any specified sources.
If no sources are specified, the
.Ic .PRECIOUS
attribute is applied to every target in the file.
.It Ic .READONLY
set the read-only attribute on the global variables specified as sources.
.It Ic .SHELL
Sets the shell that
.Nm
uses to execute commands in jobs mode.
The sources are a set of
.Ar field\| Ns Cm \&= Ns Ar value
pairs.
.Bl -tag -width ".Li hasErrCtls"
.It Li name
This is the minimal specification, used to select one of the built-in
shell specs;
.Li sh ,
.Li ksh ,
and
.Li csh .
.It Li path
Specifies the absolute path to the shell.
.It Li hasErrCtl
Indicates whether the shell supports exit on error.
.It Li check
The command to turn on error checking.
.It Li ignore
The command to disable error checking.
.It Li echo
The command to turn on echoing of commands executed.
.It Li quiet
The command to turn off echoing of commands executed.
.It Li filter
The output to filter after issuing the
.Li quiet
command.
It is typically identical to
.Li quiet .
.It Li errFlag
The flag to pass the shell to enable error checking.
.It Li echoFlag
The flag to pass the shell to enable command echoing.
.It Li newline
The string literal to pass the shell that results in a single newline
character when used outside of any quoting characters.
.El
Example:
.Bd -literal
\&.SHELL: name=ksh path=/bin/ksh hasErrCtl=true \e
	check="set \-e" ignore="set +e" \e
	echo="set \-v" quiet="set +v" filter="set +v" \e
	echoFlag=v errFlag=e newline="'\en'"
.Ed
.It Ic .SILENT
Apply the
.Ic .SILENT
attribute to any specified sources.
If no sources are specified, the
.Ic .SILENT
attribute is applied to every
command in the file.
.It Ic .STALE
This target gets run when a dependency file contains stale entries, having
.Va .ALLSRC
set to the name of that dependency file.
.It Ic .SUFFIXES
Each source specifies a suffix to
.Nm .
If no sources are specified, any previously specified suffixes are deleted.
It allows the creation of suffix-transformation rules.
.Pp
Example:
.Bd -literal
\&.SUFFIXES: .c .o
\&.c.o:
	cc \-o ${.TARGET} \-c ${.IMPSRC}
.Ed
.It Ic .SYSPATH
The sources are directories which are to be added to the system
include path which
.Nm
searches for makefiles.
If no sources are specified,
any previously specified directories are removed from the system
include path.
.El
.Sh ENVIRONMENT
.Nm
uses the following environment variables, if they exist:
.Ev MACHINE ,
.Ev MACHINE_ARCH ,
.Ev MAKE ,
.Ev MAKEFLAGS ,
.Ev MAKEOBJDIR ,
.Ev MAKEOBJDIRPREFIX ,
.Ev MAKESYSPATH ,
.Ev PWD ,
and
.Ev TMPDIR .
.Pp
.Ev MAKEOBJDIRPREFIX
and
.Ev MAKEOBJDIR
may only be set in the environment or on the command line to
.Nm
and not as makefile variables;
see the description of
.Sq Va .OBJDIR
for more details.
.Sh FILES
.Bl -tag -width /usr/share/mk -compact
.It .depend
list of dependencies
.It makefile
first default makefile if no makefile is specified on the command line
.It Makefile
second default makefile if no makefile is specified on the command line
.It sys.mk
system makefile
.It /usr/share/mk
system makefile directory
.El
.Sh COMPATIBILITY
The basic make syntax is compatible between different make variants;
however the special variables, variable modifiers and conditionals are not.
.Ss Older versions
An incomplete list of changes in older versions of
.Nm :
.Pp
The way that .for loop variables are substituted changed after
.Nx 5.0
so that they still appear to be variable expansions.
In particular this stops them being treated as syntax, and removes some
obscure problems using them in .if statements.
.Pp
The way that parallel makes are scheduled changed in
.Nx 4.0
so that .ORDER and .WAIT apply recursively to the dependent nodes.
The algorithms used may change again in the future.
.Ss Other make dialects
Other make dialects (GNU make, SVR4 make, POSIX make, etc.) do not
support most of the features of
.Nm
as described in this manual.
Most notably:
.Bl -bullet -offset indent
.It
The
.Ic .WAIT
and
.Ic .ORDER
declarations and most functionality pertaining to parallelization.
(GNU make supports parallelization but lacks the features needed to
control it effectively.)
.It
Directives, including for loops and conditionals and most of the
forms of include files.
(GNU make has its own incompatible and less powerful syntax for
conditionals.)
.\" The "less powerful" above means that GNU make does not have the
.\" make(target), target(target) and commands(target) functions.
.It
All built-in variables that begin with a dot.
.It
Most of the special sources and targets that begin with a dot,
with the notable exception of
.Ic .PHONY ,
.Ic .PRECIOUS ,
and
.Ic .SUFFIXES .
.It
Variable modifiers, except for the
.Ql :old=new
string substitution, which does not portably support globbing with
.Ql %
and historically only works on declared suffixes.
.It
The
.Ic $>
variable even in its short form; most makes support this functionality
but its name varies.
.El
.Pp
Some features are somewhat more portable, such as assignment with
.Ic += ,
.Ic ?= ,
and
.Ic != .
The
.Va .PATH
functionality is based on an older feature
.Ic VPATH
found in GNU make and many versions of SVR4 make; however,
historically its behavior is too ill-defined (and too buggy) to rely
upon.
.Pp
The
.Ic $@
and
.Ic $<
variables are more or less universally portable, as is the
.Ic $(MAKE)
variable.
Basic use of suffix rules (for files only in the current directory,
not trying to chain transformations together, etc.) is also reasonably
portable.
.Sh SEE ALSO
.Xr mkdep 1 ,
.Xr style.Makefile 5
.Sh HISTORY
A
.Nm
command appeared in
.At v7 .
This
.Nm
implementation is based on Adam de Boor's pmake program,
which was written for Sprite at Berkeley.
It was designed to be a parallel distributed make running jobs on different
machines using a daemon called
.Dq customs .
.Pp
Historically the target/dependency
.Ic FRC
has been used to FoRCe rebuilding (since the target/dependency
does not exist ... unless someone creates an
.Pa FRC
file).
.Sh BUGS
The
.Nm
syntax is difficult to parse.
For instance, finding the end of a variable's use should involve scanning
each of the modifiers, using the correct terminator for each field.
In many places
.Nm
just counts {} and () in order to find the end of a variable expansion.
.Pp
There is no way of escaping a space character in a filename.
.Pp
In jobs mode, when a target fails;
.Nm
will put an error token into the job token pool.
This will cause all other instances of
.Nm
using that token pool to abort the build and exit with error code 6.
Sometimes the attempt to suppress a cascade of unnecessary errors,
can result in a seemingly unexplained
.Ql *** Error code 6