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<TITLE> Jam - Make(1) Redux </TITLE>

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<H1> Jam - Make(1) Redux </H1>

<P> The <a href=http://www.perforce.com/jam/jam.html>Jam</a> Executable

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<DT> <P> <H2> USAGE </H2> <DD>

<PRE>
jam [ -a ] [ -g ] [ -n ] [ -q ] [ -v ]
    [ -d <I>debug</I> ] 
    [ -f <I>jambase</I> ] 
    [ -j <I>jobs</I> ] 
    [ -o <I>actionsfile</I> ] 
    [ -s <I>var</I>=<I>value</I> ] 
    [ -t <I>target</I> ] 
    [ <I>target</I> ... ]
</PRE>

<DT> <P> <H2> DESCRIPTION </H2> <DD>

	<P>

	<B>Jam</B> is a program construction tool, like <B>make</B>(1).

	<P>

	<B>Jam</B> recursively builds target files from source files,
	using dependency information and updating actions expressed in
	the Jambase file, which is written in <B>jam</B>'s own interpreted
	language.  The default Jambase is compiled into <B>jam</B> and
	provides a boilerplate for common use, relying on a user-provide
	file "Jamfile" to enumerate actual targets and sources.

	<P>

	The Jambase is described in the <a href="Jambase.html">Jambase
	Reference</a> and the document <a href="Jamfile.html">Using
	Jamfiles and Jambase</A>.

<DT> <P> <H2> OPTIONS </H2> <DD>

	<P>

	If <I>target</I> is provided on the command line, <B>jam</B>
	builds <I>target;</I> otherwise <B>jam</B> builds the target
	'all'.

	<P>

	<B>Jam</b> may be invoked with the following options:

	<P> <TABLE WIDTH=85% ALIGN=CENTER BORDER=1 CELLPADDING=2>

	    <TR><TD VALIGN=TOP WIDTH=20%><CODE> -a </CODE>
	    <TD> Build all targets anyway, even if they are up-to-date.

	    <TR><TD VALIGN=TOP><CODE> -d <I>c</I>  </CODE>
	    <TD> Turn on display option <I>c</I> and off the default 
	    display (summary info and actions):

	    <DL COMPACT>
	    <DT> a <DD> Show summary info, actions, quiet actions, and the
	    use of temporary targets
	    <DT> c <DD> Show the names of files that cause rebuilds, i.e.
	    new sources, missing targets, etc.
	    <DT> d <DD> Display a dependency graph (in <B>jam</B> syntax).
	    <DT> m <DD> Display the dependency analysis, and target/source
	    	    timestamps and paths
	    <DT> x <DD> Show shell arguments
	    </DL>

	    <TR><TD VALIGN=TOP><CODE> -d <I>n</I>  </CODE>
	    <TD> Enable cummulative debugging levels from 1 to <I>n</I>.  
	    Interesting values are:

	    <DL COMPACT>
	    <DT> 1 <DD> Show actions and summary info (the default) 
	    <DT> 3 <DD> Old name for -dm (described above)
	    <DT> 5 <DD> Show rule invocations and variable expansions 
	    <DT> 6 <DD> Show directory/header file/archive scans 
	    <DT> 7 <DD> Show variable settings 
	    <DT> 8 <DD> Show variable fetches 
	    <DT> 9 <DD> Show variable manipulation, scanner tokens 
	    </DL>

	    <TR><TD VALIGN=TOP><CODE> -d +<I>n</I> </CODE>
	    <TD> Enable debugging level <I>n</I>.

	    <TR><TD VALIGN=TOP><CODE> -d 0 </CODE>
	    <TD> Turn off all debugging levels.  Only errors are emitted.

	    <TR><TD VALIGN=TOP><CODE> -f <I>jambase</I></CODE>
	    <TD>Read <I>jambase</I> instead of using the built-in Jambase.
	    Multiple -f flags are permitted.

	    <TR><TD VALIGN=TOP><CODE> -g </CODE>
	    <TD> Build targets with the newest sources first, rather than
	    in the order of appearance in the Jambase/Jamfiles.

	    <TR><TD VALIGN=TOP><CODE> -j <I>n</I></CODE>
	    <TD> Run up to <I>n</I> shell commands concurrently (UNIX 
	    and NT only).  The default is 1.

	    <TR><TD VALIGN=TOP><CODE> -n</CODE>
	    <TD> Don't actually execute the updating actions, but do
	    everything else.  This changes the debug level to -dax.

	    <TR><TD VALIGN=TOP><CODE> -o <I>file</I></CODE>
	    <TD> Write the updating actions to the specified file instead
	    of running them (or outputting them, as on the Mac).

	    <TR><TD VALIGN=TOP><CODE> -q </CODE>
	    <TD> Quit quickly (as if an interrupt was received)
	    as soon as any target build fails.

	    <TR><TD VALIGN=TOP><CODE> -s <I>var</I>=<I>value</I></CODE>
	    <TD> Set the variable <I>var</I> to <I>value</I>, overriding
	    both internal variables and variables imported from the
	    environment.

	    <TR><TD VALIGN=TOP><CODE> -t <I>target</I></CODE>
	    <TD> Rebuild <I>target</I> and everything that depends on it, 
	     even if it is up-to-date.

	    <TR><TD VALIGN=TOP><CODE> -v</CODE>
	    <TD> Print the version of <B>jam</B> and exit.

	</TABLE>

<DT> <P> <H2> OPERATION </H2> <DD>

	<P>

	<b>Jam</b> has four phases of operation: start-up, parsing, 
	binding, and updating.

<DT> <P> <H3> Start-up </H3> <DD>

	<P>

	Upon start-up, <b>jam</b> imports environment variable settings
	into <b>jam</b> variables.  Environment variables are split at
	blanks with each word becoming an element in the variable's list
	of values.  Environment variables whose names end in PATH are
	split at $(SPLITPATH) characters (e.g., ":" for Unix).

	<P>

	To set a variable's value on the command line, overriding the
	variable's environment value, use the -s option.  To see variable
	assignments made during <b>jam</b>'s execution, use the -d+7
	option.

<DT> <P> <H3> Parsing </H3> <DD>

	<P>

	In the parsing phase, <b>jam</b> reads and executes the Jambase
	file, by default the built-in one.  It is written in the <b>jam</b>
	language.  See <a href="#language"> Language</a> below.  The
	last action of the Jambase is to read (via the "include" rule)
	a user-provided file called "Jamfile".

	<P>

	Collectively, the purpose of the Jambase and the Jamfile is to
	name built target and source files, construct the dependency
	graph among them, and associate build actions with targets.
	The Jambase defines boilerplate rules and variable assignments,
	and the Jamfile uses these to specify the actual relationship
	among the target and source files.  See the <a
	href="Jambase.html">Jambase Reference</a> and the document <a
	href="Jamfile.html">Using Jamfiles and Jambase</A> for information.

<A NAME="binding">
<DT> <P> <H3> Binding </H3> <DD>
</A>

	<P> <H5> Binding </H5>

	After parsing, <B>jam</B> recursively descends the dependency
	graph and binds every file target with a location in the
	filesystem.  

	<P> <H5> Targets </H5> <DD>

	Any string value in <b>jam</b> can represent a target, and it
	does so if the DEPENDS or INCLUDES rules make it part of the
	dependency graph.  Build targets are files to be updated.  Source
	targets are the files used in updating build targets.  Build
	targets and source targets are collectively referred to as file
	targets, and frequently build targets are source targets for
	other build targets.  Pseudotargets are symbols which represent
	dependencies on other targets, but which are not themselves
	associated with any real file.

	<P>

	A file target's identifier is generally the file's name, which can
	be absolutely rooted, relative to the directory of <b>jam</b>'s
	invocation, or simply local (no directory).  Most often it is the
	last case, and the actual file path is bound using the $(SEARCH)
	and $(LOCATE) special variables.  See <A HREF="#search"> SEARCH
	and LOCATE Variables</A> below.  A local filename is optionally
	qualified with "grist," a string value used to assure uniqueness.
	A file target with an identifier of the form <I>file(member)</I>
	is a library member (usually an ar(1) archive on UNIX).

	<P>

	The use of $(SEARCH) and $(LOCATE) allows <b>jam</b> to separate
	the the location of files from their names, so that Jamfiles can
	refer to files locally (i.e. relative to the Jamfile's directory),
	yet still be usable when <b>jam</b> is invoked from a distant
	directory.  The use of grist allows files with the same name
	to be identified uniquely, so that <b>jam</b> can read a whole
	directory tree of Jamfiles and not mix up same-named targets.

	<P> <H5> Update Determination </H5>

	After binding each target, <B>jam</B> determines whether the
	target needs updating, and if so marks the target for the updating
	phase.  A target is normally so marked if it is missing, it is
	older than any of its sources, or any of its sources are marked
	for updating.  This behavior can be modified by the application
	of special built-in rules.  See <A HREF="#bindingmods">Modifying
	Binding</A> below.

	<P> <H5> Header File Scanning </H5>

	During the binding phase, <b>jam</b> also performs header file
	scanning, where it looks inside source files for the implicit
	dependencies on other files caused by C's #include syntax.  This
	is controlled by the special variables $(HDRSCAN) and $(HDRRULE).
	The result of the scan is formed into a rule invocation, with
	the scanned file as the target and the found included file names
	as the sources.  Note that this is the only case where rules
	are invoked outside the parsing phase.  See <A
	HREF="#hdrscan">HDRSCAN and HDRRULE Variables</A> below.

<DT> <P> <H3> Updating </H3> <DD>

	<P>

	After binding, <B>jam</B> again recursively descends the dependency
	graph,  this time executing the update actions for each target
	marked for update during the binding phase.  If a  target's
	updating actions fail, then all other targets which depend on
	that target are skipped.

	<P>

	The -j flag instructs <B>jam</B> to build more than one target
	at a time.  If there are multiple actions on a single target,
	they are run sequentially.   The -g flag reorders builds so that
	targets with newest sources are built first.  Normally, they are
	built in the order of appearance in the Jamfiles.

<A NAME="language">
<DT> <P> <H2> LANGUAGE </H2> <DD>
</A>

<DT> <P> <H3> Overview </H3> <DD>

	<B>Jam</b> has a interpreted, procedural language with a few
	select features to effect program construction.  Statements in
	<b>jam</b> are rule (procedure) definitions, rule invocations,
	updating action definitions, flow-of-control structures, variable
	assignments, and sundry language support.

<DT> <P> <H3> Lexical Features </H3> <DD>

	<P>

	<B>Jam</b> treats its input files as whitespace-separated tokens,
	with two exceptions: double quotes (") can enclose whitespace to
	embed it into a token, and everything between the matching curly
	braces ({}) in the definition of a updating actions is treated
	as a single string.  A backslash (\) can escape a double quote,
	or any single whitespace character.

	<P>

	<B>Jam</b> requires whitespace (blanks, tabs, or newlines) to
	surround all tokens, <b>including the colon (:) and semicolon
	(;) tokens</b>.

	<P>

	<B>Jam</b> keywords (as mentioned in this document) are reserved
	and generally must be quoted with double quotes (") to be used
	as arbitrary tokens, such as variable or target names.

<DT> <P> <H3> Datatype </H3> <DD>

	<P>

	<B>Jam</B>'s only data type is a one-dimensional list of arbitrary
	strings.  They arise as literal (whitespace-separated) tokens in
	the Jambase or included files, as the result of variable expansion
	of those tokens, or as the return value from a rule invocation.

<DT> <P> <H3> Rules </H3> <DD>

	<P>

	The basic <B>jam</b> language entity is called a rule.	A rule
	is simply a procedure definition, with a body of <b>jam</b>
	statements to be run when the rule is invoked.  The syntax of
	rule invocation make it possible to write Jamfiles that look
	a bit like Makefiles.

	<P>

	Rules take up to 9 arguments ($(1) through $(9), each a list)
	and can have a return value (a single list).  A rule's return
	value can be expanded in a list by enclosing the rule invocation
	with <tt>[</tt> and <tt>]</tt>.

<DT> <P> <H3> Updating Actions </H3> <DD>

	<P>

	A rule may have updating actions associated with it, in which
	case arguments $(1) and $(2) are treated as built targets and
	sources, respectively.	Updating actions are the OS shell commands
	to execute when updating the built targets of the rule.

	<P>

	When an rule with updating actions is invoked, those actions are
	added to those associated with its built targets ($(1)) before
	the rule's procedure is run.  Later, to build the targets in the
	updating phase, the actions are passed to the OS command shell,
	with $(1) and $(2) replaced by bound versions of the target names.
	See <A HREF="#binding"> Binding</A> above.


<DT> <P> <H3> Statements </H3> <DD>

	<P>

	<b>Jam</b>'s langauge has the following statements:

	<P><TABLE WIDTH=75% ALIGN=CENTER><TR><TD><DL>

	    <P> <DT> <CODE>
	    
		<I>rulename field1</I> : <I>field2</I> : <I>...</I> 
	    	: <I>fieldN</I> ;

	    </CODE>

	    <P><DD> Invoke a rule.  A rule is invoked with values in
	    <I>field1</I> through <I>fieldN</I> (9 max).  They may be
	    referenced in the procedure's <I>statements</I> as $(1)
	    through $(<9>N</I>).  $(&lt;) and $(&gt;) are synonymous
	    with $(1) and $(2).

	    <P>
	    <i>rulename</i> undergoes <A HREF="#varexp"> variable
	    expansion</A>.  If the resulting list is more than one value,
	    each rule is invoked with the same arguments, and the result
	    of the invocation is the concatenation of all the results.

	    <P> <DT> <CODE>

		actions [ <I>modifiers</I> ] <I>rulename</I> { <I>commands</I> }

	    </CODE>

	    <P><DD> Define a rule's updating actions, replacing any previous
	    definition.  The first two arguments may be referenced in
	    the action's <I>commands</I> as $(1) and $(2) or $(&lt;)
	    and $(&gt;).

	    <P>

	    The following action <i>modifiers</i> are understood:

	    <P><TABLE BORDER=1>

		<TR><TD WIDTH=30%><CODE> actions bind <I>vars</I> </CODE></TD>
		<TD> $(vars) will be replaced with bound values.</TD>
		</TR>

		<TR><TD><CODE> actions existing </CODE></TD>
		<TD> $(>) includes only source targets currently existing.</TD>
		</TR>

		<TR><TD><CODE> actions ignore </CODE></TD>
		<TD> The return status of the <I>commands</I> is ignored.</TD>
		</TR>

		<TR><TD><CODE> actions piecemeal </CODE></TD>
		<TD> <I>commands</I>  are repeatedly invoked with a subset
		of $(>) small enough to fit in the command buffer on this
		OS.</TD>
		</TR>

		<TR><TD><CODE> actions quietly </CODE></TD>
		<TD> The action is not echoed to the standard output.</TD>
		</TR>

		<TR><TD><CODE> actions together </CODE></TD>
		<TD> The $(>) from multiple invocations of the same action
		on the same built target are glommed together.</TD>
		</TR>

		<TR><TD><CODE> actions updated </CODE></TD>
		<TD> $(>) includes only source targets themselves marked
		for updating.</TD>
		</TR>

	    </TABLE>

	    <P><DT><CODE> 

		break 

	    </CODE>

	    <P><DD> Breaks out of the closest enclosing <I>for</I>
	    or <I>while</I> loop.

	    <P><DT><CODE> 

		continue 

	    </CODE>

	    <P><DD> Jumps to the end of the closest enclosing <I>for</I>
	    or <I>while</I> loop.

	    <P><DT><CODE> 

		for <I>var</I> in <I>list</I> { <I>statements</I> }

	    </CODE>

	    <P><DD> Executes <i>statements</i> for each element in
	    <i>list</i>, setting the variable <i>var</i> to the element
	    value.

	    <A name=if>
	    <P><DT><CODE>
	    </A>

		if <I>cond</I> { <I>statements</I> } [ else <I>statement</I> ]

	    </CODE>

	    <P><DD> Does the obvious;  the else clause is optional.
	    <i>cond</i> is built of:

	    <TABLE BORDER=1> 

		<TR><TD WIDTH=25%> <CODE><I>a</I></CODE></TD>
		<TD> true if any <I>a</I> element is a non-zero-length 
		string</TD>
		<TR><TD> <CODE><I>a</I> = <I>b</I></CODE> </TD>
		<TD> list <I>a</I> matches list <I>b</I> 
		string-for-string</TD>
		<TR><TD> <CODE><I>a</I> != <I>b</I> </CODE></TD>
		<TD> list <I>a</I> does not match list <I>b</I></TD>
		<TR><TD> <CODE><I>a</I> &lt; <I>b</I> </CODE></TD>
		<TD> <I>a[i]</I> string is less than <I>b[i]</I>
		string, where <i>i</i> is first mismatched element
		in lists <I>a</I> and <I>b</I></TD>
		<TR><TD> <CODE><I>a</I> &lt;= <I>b</I> </CODE></TD>
		<TD> every <I>a</I> string is less than or equal to
		its <I>b</I> counterpart</TD>
		<TR><TD> <CODE><I>a</I> &gt; <I>b</I> </CODE></TD>
		<TD> <I>a[i]</I> string is greater than <I>b[i]</I>
		string, where <i>i</i> is first mismatched element</TD>
		<TR><TD> <CODE><I>a</I> &gt;= <I>b</I> </CODE></TD>
		<TD> every <I>a</I> string is greater than or equal to
		its <I>b</I> counterpart</TD>
		<TR><TD> <CODE><I>a</I> in <I>b</I> </CODE></TD>
		<TD> true if all elements of <I>a</I> can be found
		in <I>b</I>, or if <I>a</I> has no elements</TD>
		<TR><TD> <CODE>! <I>cond</I> </CODE></TD>
		<TD> condition not true</TD>
		<TR><TD> <CODE><I>cond</I> && <I>cond</I> </CODE></TD>
		<TD> conjunction</TD>
		<TR><TD> <CODE><I>cond</I> || <I>cond</I> </CODE></TD>
		<TD> disjunction</TD>
		<TR><TD> <CODE>( <I>cond</I> ) </CODE></TD>
		<TD> precedence grouping</TD>

	    </TABLE>

	    <P><DT> <CODE>

		include <I>file</I> ;

	    </CODE>

	    <P><DD> Causes <b>jam</b> to read the named <i>file</i>.
	    The file is bound like a regular target (see <A
	    HREF="#binding"> Binding</A> above) but unlike a regular
	    target the include file cannot be built.  Marking an include
	    file target with the <b>NOCARE</b> rule makes it optional:
	    if it is missing, it causes no error.

	    <P>

	    The include file is inserted into the input stream during
	    the parsing phase. The primary input file and all the included
	    file(s) are treated as a single file; that is, <b>jam</b>
	    infers no scope boundaries from included files.

	    <P><DT> <CODE>

		local <i>vars</I> [ = <i>values</i> ] ;

	    </CODE>

	    <P><DD> Creates new <i>vars</i> inside to the enclosing {}
	    block, obscuring any previous values they might have.  The
	    previous values for <i>vars</i> are restored when the current
	    block ends.  Any rule called or file included will see the
	    local and not the previous value (this is sometimes called
	    Dynamic Scoping).  The local statement may appear anywhere,
	    even outside of a block (in which case the previous value
	    is restored when the input ends).  The <i>vars</i> are
	    initialized to <i>values</i> if present, or left uninitialized
	    otherwise.

	    <P> <DT> <CODE>
	    
		on <I>target</I> <I>statement</I> ;

	    </CODE>

	    <P><DD> Run <I>statement</I> under the influence of
	    <I>target</I>'s target-specific variables.  These variables
	    become local copies during <I>statement</I>'s run, but they
	    may be updated as target-specific variables using the usual
	    "<I>variable</I> on <I>targets</I> =" syntax.


	    <P><DT> <CODE>

		return <I>values</I> ; 

	    </CODE>

	    <P><DD> Within a rule body, the return statement sets the return
	    value for an invocation of the rule and terminates the rule's
	    execution.

	    <P> <DT> <CODE>
	    
		rule <I>rulename</I> [ : <I>vars</I> ] { <I>statements</I> }

	    </CODE>

	    <P><DD> Define a rule's procedure, replacing any previous
	    definition.  If <I>vars</I> are provided, they are assigned
	    the values of the parameters ($(1) to $(9)) when <I>statements</I>
	    are executed, as with the <B>local</B> statement.

	    <P><DT> <CODE>

		<A NAME="switch">
		switch <I>value</I>
		</A>
		<BR> { 
		<BR> case <I>pattern1</I> : <I>statements</I> ; 
		<BR> case <I>pattern2</I> : <I>statements</I> ; 
		<BR> ... 
		<BR> }

	    </CODE>

	    <P><DD> The switch statement executes zero or one of the
	    enclosed <i>statements</i>, depending on which, if any, is
	    the first case whose <i>pattern</I> matches <i>value</i>.
	    The <i>pattern</I> values are not variable-expanded.  The
	    <i>pattern</I>  values may include the following wildcards:

	    <TABLE>

		<TR><TD><CODE> ? </CODE></TD>
		<TD> match any single character </TD>
		<TR><TD><CODE> * </CODE></TD>
		<TD> match zero or more characters </TD>
		<TR><TD><CODE> [<i>chars</i>] </CODE></TD>
		<TD> match any single character in <i>chars</i> </TD>
		<TR><TD><CODE> [^<i>chars</i>] </CODE></TD>
		<TD> match any single character not in <i>chars</i> </TD>
		<TR><TD><CODE> \<i>x</i> </CODE></TD>
		<TD> match <i>x</i> (escapes the other wildcards)</i> </TD>

	    </TABLE>

	    <P><DT> <CODE>

		while <I>cond</I> { <I>statements</I> }

	    </CODE>

	    <P><DD> Repeatedly execute <I>statements</I> while <I>cond</I>
	    remains true upon entry. (See the description of <I>cond</I>
	    expression syntax under <a href="#if">if</a>, above).
	</DL></TABLE>


<DT> <P> <H3> Variables </H3> <DD>

	<P>

	<B>Jam</b> variables are lists of zero or more elements, with
	each element being a string value.  An undefined variable is
	indistinguishable from a variable with an empty list, however,
	a defined variable may have one more elements which are null
	strings.  All variables are referenced as $(<I>variable</I>).

	<P>

	Variables are either global or target-specific.  In the latter
	case, the variable takes on the given value only during the
	target's binding, header file scanning, and updating; and during
	the "on <I>target</I> <I>statement</I>" statement.

	<P>

	A variable is defined with:

	<P> <TABLE WIDTH=75% ALIGN=CENTER> <TR><TD> <DL>

	    <DT><CODE> 
	    <I>variable</I> = <I>elements</I> ; </CODE>
	    <DT><CODE> 
	    <I>variable</I> += <I>elements</I> ; </CODE>
	    <DT><CODE> 
	    <I>variable</I> ?= <I>elements</I> ; </CODE>
	    <DT><CODE> 
	    <I>variable</I> on <I>targets</I> = <I>elements</I> ; </CODE>
	    <DT><CODE> 
	    <I>variable</I> on <I>targets</I> += <I>elements</I> ; </CODE>
	    <DT><CODE> 
	    <I>variable</I> on <I>targets</I> ?= <I>elements</I> ; </CODE>

	</DL></TABLE>

	<P>

	The first three forms set <I>variable</I> globally.  The last
	three forms set a target-specific variable.  The = operator
	replaces any previous elements of <I>variable</I> with
	<I>elements</I>; the += operation adds <I>elements</I> to
	<I>variable</I>'s list of elements; the ?= operator sets
	<I>variable</I> only if it was previously unset.  The last form
	"<I>variable</I> on <I>targets</I> ?= <I>elements</I>" checks
	to see if the target-specific, not the global, variable is set.
	(The ?= operator also has an old form "default =".)  

	<P>

	Variables referenced in updating commands will be replaced with
	their values; target-specific values take precedence over global
	values.  Variables passed as arguments ($(1) and $(2)) to actions
	are replaced with their bound values; the "bind" modifier can
	be used on actions to cause other variables to be replaced with
	bound values.  See <A HREF="#actionmods">Action Modifiers</A>
	above.

	<P>

	<B>Jam</b> variables are not re-exported to the environment of
	the shell that executes the updating actions, but the updating
	actions can reference <b>jam</b> variables with $(<I>variable</I>).

<A NAME="varexp">
<DT> <P> <H3> Variable Expansion </H3> <DD>
</A>

	<P>

	During parsing, <b>jam</b> performs variable expansion on each
	token that is not a keyword or rule name.  Such tokens with
	embedded variable references are replaced with zero or more
	tokens.  Variable references are of the form $(<I>v</I>) or
	$(<I>vm</I>), where <i>v</i> is the variable name,  and  <I>m</I>
	are optional modifiers.

	<P>

	Variable expansion in a rule's actions is similar to variable
	expansion in statements,  except that the action string is
	tokenized at whitespace regardless of quoting.

	<P>

	The result of a token after variable expansion is the
	<i>product</i> of the components of the token, where each
	component is a literal substring or a list substituting a variable
	reference.  For example:

	<P> <TABLE WIDTH=75% ALIGN=CENTER><TR><TD><CODE>

	    <BR>$(X)      -> a b c
	    <BR>t$(X)     -> ta tb tc
	    <BR>$(X)z     -> az bz cz
	    <BR>$(X)-$(X) -> a-a a-b a-c b-a b-b b-c c-a c-b c-c

	</CODE></TABLE>

	<P>

	The variable name and modifiers can themselves contain
	a variable reference,  and this partakes of the product
	as well:

	<P> <TABLE WIDTH=75% ALIGN=CENTER><TR><TD><CODE>

	    <BR>$(X)      -> a b c
	    <BR>$(Y)      -> 1 2
	    <BR>$(Z)      -> X Y
	    <BR>$($(Z))   -> a b c 1 2

	</CODE></TABLE>

	<P>

	Because of this product expansion, if any variable reference in
	a token is undefined, the result of the expansion is an empty
	list.  If any variable element is a null string, the result
	propagates the non-null elements:

	<P> <TABLE WIDTH=75% ALIGN=CENTER><TR><TD><CODE>

	    <BR>$(X)        -> a ""
	    <BR>$(Y)        -> "" 1
	    <BR>$(Z)	  -> 
	    <BR>*$(X)$(Y)*  -> *a* *a1* ** *1*
	    <BR>*$(X)$(Z)*  ->

	</CODE></TABLE>

	<P>

	A variable element's string value can be parsed into grist and
	filename-related components.  Modifiers to a variable are used
	to select elements, select components, and replace components.
	The modifiers are:

	<P> <TABLE WIDTH=75% BORDER=1 ALIGN=CENTER>

	    <TR><TD><CODE> [<I>n</I>] </CODE>
	    <TD>Select element number <I>n</I> (starting at 1).  If
	    the variable contains fewer than <I>n</I> elements,
	    the result is a zero-element list.

	    <TR><TD><CODE> [<I>n</I>-<I>m</I>] </CODE>
	    <TD>Select elements number <I>n</I> through <I>m</I>.

	    <TR><TD><CODE> [<I>n</I>-] </CODE>
	    <TD>Select elements number <I>n</I> through the last.

	    <TR><TD><CODE> :B </CODE>
	    <TD>Select filename base.

	    <TR><TD><CODE> :S </CODE>
	    <TD>Select (last) filename suffix.

	    <TR><TD><CODE> :M </CODE>
	    <TD>Select archive member name.

	    <TR><TD><CODE> :D </CODE>
	    <TD>Select directory path.

	    <TR><TD><CODE> :P </CODE>
	    <TD>Select parent directory.

	    <TR><TD><CODE> :G </CODE>
	    <TD>Select grist.

	    <TR><TD><CODE> :U </CODE>
	    <TD>Replace lowercase characters with uppercase.

	    <TR><TD><CODE> :L </CODE>
	    <TD>Replace uppercase characters with lowercase.

	    <TR><TD><CODE> :<i>chars</I> </CODE>
	    <TD>Select the components listed in <i>chars</i>.

	    <TR><TD><CODE> :G=<I>grist</I> </CODE>
	    <TD>Replace grist with <I>grist</I>.

	    <TR><TD><CODE> :D=<I>path</I> </CODE>
	    <TD>Replace directory with <I>path</I>.

	    <TR><TD><CODE> :B=<I>base</I> </CODE>
	    <TD>Replace the base part of file name with <I>base</I>.

	    <TR><TD><CODE> :S=<I>suf</I> </CODE>
	    <TD>Replace the suffix of file name with <I>suf</I>.

	    <TR><TD><CODE> :M=<I>mem</I> </CODE>
	    <TD>Replace the archive member name with <I>mem</I>.

	    <TR><TD><CODE> :R=<I>root</I> </CODE>
	    <TD>Prepend <I>root</I> to the whole file name,  if not
	    already rooted.

	    <TR><TD><CODE> :E=<I>value</I> </CODE>
	    <TD>Use <I>value</I> instead if the variable is unset.

	    <TR><TD><CODE> :J=<I>joinval</I> </CODE>
	    <TD>Concatentate list elements into single
            element, separated by <I>joinval</I>.

	</TABLE>

	<P>

	On VMS, $(var:P) is the parent directory of $(var:D); on Unix
	and NT, $(var:P) and $(var:D) are the same.


<DT> <P> <H3> Built-in Rules </H3> <DD>

	<P>
	<B>Jam</b> has twelve built-in rules, all of which are pure
	procedure rules without updating actions.  They are in
	three groups:  the first builds the dependency graph;
	the second modifies it; and the third are just utility
	rules.

	<P> <H5> Dependency Building </H5> 

	<P><TABLE WIDTH=75% ALIGN=CENTER><TR><TD><DL>

	<P><DT><CODE> 
	DEPENDS <I>targets1</I> : <I>targets2</I> ; 
	</CODE>

	<DD> Builds a direct dependency: makes each of <I>targets1</I>
	depend on each of <I>targets2</I>.  Generally, <I>targets1</I>
	will be rebuilt if <I>targets2</I> are themselves rebuilt are
	or are newer than <I>targets1</I>.

	<P><DT><CODE>
	INCLUDES <I>targets1</I> : <I>targets2</I> ;
	</CODE>

	<DD> Builds a sibling dependency: makes any target that depends
	on any of <I>targets1</I> also depend on each of <I>targets2</I>.
	This reflects the dependencies that arise when one source file
	includes another:  the object built from the source file depends
	both on the original and included source file,  but the two
	sources files don't depend on each other.  For example:

	<CODE>
	<P>DEPENDS foo.o : foo.c ;
	<BR>INCLUDES foo.c : foo.h ;
	</CODE>

	<P>

	"foo.o" depends on "foo.c" and "foo.h" in this example.

	</DL></TABLE>

	<A NAME="bindingmods">
	<P> <H5> Modifying Binding </H5> 
	</A>

	<P>

	The six rules ALWAYS, LEAVES, NOCARE, NOTFILE, NOUPDATE, and
	TEMPORARY modify the dependency graph so that <b>jam</b> treats
	the targets differently during its target binding phase.  See
	<A HREF="#binding">Binding</A> above.  Normally, <b>jam</b>
	updates a target if it is missing, if its filesystem modification
	time is older than any of its dependencies (recursively), or if
	any of its dependencies are being updated.  This basic behavior
	can be changed by invoking the following rules:

	<P><TABLE WIDTH=75% ALIGN=CENTER><TR><TD><DL>

	<P><DT><CODE>
	ALWAYS <I>targets</I> ;
	</CODE>

	<DD> Causes <I>targets</I> to be rebuilt regardless of whether
	they are up-to-date (they must still be in the dependency graph).
	This is used for the clean and uninstall targets, as they have
	no dependencies and would otherwise appear never to need building.
	It is best applied to targets that are also NOTFILE targets,
	but it can also be used to force a real file to be updated as
	well.

	<P><DT><CODE>
	LEAVES <I>targets</I> ;
	</CODE>

	<DD> Makes each of <I>targets</I> depend only on its leaf sources,
	and not on any intermediate targets.  This makes it immune to
	its dependencies being updated, as the "leaf" dependencies are
	those without their own dependencies and without updating actions.
	This allows a target to be updated only if original source files
	change.

	<P><DT><CODE>
	NOCARE <I>targets</I> ;
	</CODE>

	<DD> Causes <b>jam</b> to ignore <I>targets</I> that neither
	can be found nor have updating actions to build them.  Normally
	for such targets <B>jam</B> issues a warning and then skips
	other targets that depend on these missing targets.  The HdrRule
	in Jambase uses NOCARE on the header file names found during
	header file scanning, to let <b>jam</b> know that the included
	files may not exist.   For example,  if a #include is within an
	#ifdef, the included file may not actually be around.

	<P><DT><CODE>
	NOTFILE <I>targets</I> ;
	</CODE>

	<DD> Marks <I>targets</I> as pseudotargets and not real files.
	No timestamp is checked, and so the actions on such a target
	are only executed if the target's dependencies are updated, or
	if the target is also marked with ALWAYS.  The default <b>jam</b>
	target "all" is a pseudotarget. In Jambase, NOTFILE is used to
	define several addition convenient pseudotargets.

	<P><DT><CODE>
	NOUPDATE <I>targets</I> ;
	</CODE>

	<DD> Causes the timestamps on <I>targets</I> to be ignored.
	This has two effects:  first,  once the target has been created
	it will never be updated; second, manually updating target will
	not cause other targets to be updated.  In Jambase, for example,
	this rule is applied to directories by the MkDir rule, because
	MkDir only cares that the target directory exists, not when it
	has last been updated.

	<P><DT><CODE>
	TEMPORARY <I>targets</I> ;
	</CODE>

	<DD> Marks <I>targets</I> as temporary, allowing them to be
	removed after other targets that depend upon them have been
	updated.  If a TEMPORARY target is missing, <b>jam</b> uses the
	timestamp of the target's parent.  Jambase uses TEMPORARY to
	mark object files that are archived in a library after they are
	built, so that they can be deleted after they are archived.

	</DL></TABLE>

	<P> <H5> Utility Rules </H5> 

	The remaining rules are utility rules.

	<P><TABLE WIDTH=75% ALIGN=CENTER><TR><TD><DL>

	<P><DT><CODE>
	ECHO <i>args</I> ; <br>
	Echo <i>args</I> ; <br>
	echo <i>args</I> ;
	</CODE>

	<DD> Blurts out the message <i>args</I> to stdout.

	<P><DT><CODE>
	EXIT <i>args</I> ; <br>
	Exit <i>args</I> ; <br>
	exit <i>args</I> ;
	</CODE>

	<DD> Blurts out the message <i>args</I> to stdout and then exits
	with a failure status.

	<P><DT><CODE>
	GLOB <i>directories</I> : <I>patterns</I> ;
	</CODE>

	<DD> Scans <i>directories</i> for files matching <i>patterns</i>,
	returning the list of matching files (with directory prepended).
	<i>patterns</i> uses the same syntax as in the <b>switch</b>
	statement.  Only useful within the <tt>[ ]</tt> construct, to
	change the result into a list.

	<P><DT><CODE>
	MATCH <i>regexps</I> : <I>list</I> ;
	</CODE>

	<DD> Matches the <b>egrep</b>(1) style regular expressions
	<I>regexps</I> against the strings in <I>list</I>.  The result
	is the concatenation of matching <tt>()</tt> subexpressions for
	each string in <I>list</I>, and for each regular expression in
	<I>regexps</I>.  Only useful within the <tt>[ ]</tt> construct,
	to change the result into a list.

	</DL></TABLE>

<DT> <P> <H3> Built-in Variables </H3> <DD>

	<P>

	This section discusses variables that have special meaning to
	<b>jam</b>.

	<A NAME="search">
	<P> <H4> SEARCH and LOCATE Variables </H4>
	</A>

	<P>

	These two variables control the binding of file target names to
	locations in the file system.  Generally, $(SEARCH) is used to
	find existing sources while $(LOCATE) is used to fix the location
	for built targets.

	<P>

	Rooted (absolute path) file targets are bound as is.  Unrooted
	file target names are also normally bound as is, and thus relative
	to the current directory, but the settings of $(LOCATE) and
	$(SEARCH) alter this:

	<P>

	<UL>

	<LI> If $(LOCATE) is set then the target is bound relative to
	the first directory in $(LOCATE).  Only the first element is
	used for binding.

	<LI> If $(SEARCH) is set then the target is bound to the first
	directory in $(SEARCH) where the target file already exists.

	<LI> If the $(SEARCH) search fails, the target is bound relative
	to the current directory anyhow.

	</UL>

	<P>

	Both $(SEARCH) and $(LOCATE) should be set target-specific and
	not globally.  If they were set globally,  <b>jam</b> would use
	the same paths for all file binding, which is not likely to
	produce sane results.  When writing your own rules,  especially
	ones not built upon those in Jambase, you may need to set
	$(SEARCH) or $(LOCATE) directly.  Almost all of the rules defined
	in Jambase set $(SEARCH) and $(LOCATE) to sensible values for
	sources they are looking for and targets they create, respectively.

	<A NAME="hdrscan">
	<P> <H4> HDRSCAN and HDRRULE Variables </H4>
	</A>

	<P>

	These two variable control header file scanning.  $(HDRSCAN) is
	an <b>egrep</b>(1) pattern, with ()'s surrounding the file name,
	used to find file inclusion statements in source files.  Jambase
	uses $(HDRPATTERN) as the pattern for $(HDRSCAN).  $(HDRRULE)
	is the name of a rule to invoke with the results of the scan:
	the scanned file is the target, the found files are the sources.
	$(HDRRULE) is run under the influence of the scanned file's
	target-specific variables.

	<P>

	Both $(HDRSCAN) and $(HDRRULE) must be set for header file
	scanning to take place, and they should be set target-specific
	and not globally.  If they were set globally, all files, including
	executables and libraries, would be scanned for header file
	include statements.

	<P>

	The scanning for header file inclusions is not exact, but it is
	at least dynamic, so there is no need to run something like
	<b>makedepend</b>(GNU) to create a static dependency file. The
	scanning mechanism errs on the side of inclusion (i.e., it is
	more likely to return filenames that are not actually used by
	the compiler than to miss include files) because it can't tell
	if #include lines are inside #ifdefs or other conditional logic.
	In Jambase, HdrRule applies the NOCARE rule to each header file
	found during scanning so that if the file isn't present yet
	doesn't cause the compilation to fail, <b>jam</b> won't care.

	<P>

	Also, scanning for regular expressions only works where the
	included file name is literally in the source file.  It can't
	handle languages that allow including files using variable names
	(as the Jam language itself does).

	<P> <H4> Platform Identifier Variables </H4>

	<P>

	A number of Jam built-in variables can be used to identify
	runtime platform:

	<P>

	<TABLE WIDTH=75% ALIGN=CENTER>

	    <TR><TD>OS<TD>OS identifier string 
	    <TR><TD>OSPLAT<TD>Underlying architecture, when applicable
	    <TR><TD>MAC<TD>true on MAC platform
	    <TR><TD>NT<TD>true on NT platform
	    <TR><TD>OS2<TD>true on OS2 platform
	    <TR><TD>UNIX<TD>true on Unix platforms
	    <TR><TD>VMS<TD>true on VMS platform

	</TABLE>

	<P> <H4> Jam Version Variables </H4>

	<P>

	<TABLE WIDTH=75% ALIGN=CENTER>

	    <TR><TD>JAMDATE<TD>Time and date at <b>jam</b> start-up.
	    <TR><TD>JAMUNAME<TD>Ouput of <b>uname</b>(1) command (Unix only)
	    <TR><TD>JAMVERSION<TD><b>jam</b> version, as reported by jam -v.

	</TABLE>

	<P> <H4> JAMSHELL Variable </H4>

	<P>

	When  <b>jam</b>  executes a  rule's action block, it forks and
	execs a shell, passing the action block as an argument to the
	shell.   The invocation of the shell can be controlled by
	$(JAMSHELL).  The default on Unix is, for example:

	<P>

	<CODE>JAMSHELL = /bin/sh -c % ;</CODE>

	<P>

	The % is replaced with the text of the action block.

	<P>

	<B>Jam</b>  does not directly support building in parallel across
	multiple hosts, since that is heavily dependent on the local
	environment.   To build in parallel across multiple hosts, you
	need to write your own shell that provides access to the multiple
	hosts.  You then reset $(JAMSHELL) to reference it.

	<P>

	Just as <b>jam</b> expands a % to be the text of the rule's
	action block, it expands a ! to be the multi-process slot number.
	The slot number varies between 1 and the number of concurrent
	jobs permitted by the -j flag given on the command line.  Armed
	with this, it is possible to write a multiple host shell.  For
	example:

	<P>

	<TABLE WIDTH=75% ALIGN=CENTER><TR><TD><CODE>

	    <BR>#!/bin/sh
	    <BR>
	    <BR># This sample JAMSHELL uses the SunOS on(1) command to execute a
	    <BR># command string with an identical environment on another host.
	    <BR>
	    <BR># Set JAMSHELL = jamshell ! %
	    <BR>#
	    <BR># where jamshell is the name of this shell file.
	    <BR>#
	    <BR># This version handles up to -j6; after that they get executed
	    <BR># locally.
	    <BR>
	    <BR>case $1 in
	    <BR>1|4) on winken sh -c "$2";;
	    <BR>2|5) on blinken sh -c "$2";;
	    <BR>3|6) on nod sh -c "$2";;
	    <BR>*)   eval "$2";;
	    <BR>esac

	</CODE></TABLE>


<DT> <P> <H2> DIAGNOSTICS </H2>  <DD>

	<P>

       In addition to generic error messages, <B>jam</B> may emit one of
       the following:

       <P><TABLE WIDTH=75% ALIGN=CENTER><TR><TD><DL>

       <P><DT><CODE> warning: unknown rule X </CODE> <DD>

              A rule was invoked that has not been defined with
              an "actions" or "rule" statement.

       <P><DT><CODE> using N temp target(s) </CODE> <DD>

              Targets marked as being temporary (but nonetheless
              present) have been found.

       <P><DT><CODE> updating N target(s) </CODE> <DD>

              Targets are out-of-date and will be updated.

       <P><DT><CODE> can't find N target(s) </CODE> <DD>

              Source files can't be found and there are no
              actions to create them.

       <P><DT><CODE> can't make N target(s) </CODE> <DD>

              Due to sources not being found, other targets cannot be made.

       <P><DT><CODE> warning: X depends on itself </CODE> <DD>

              A target depends on itself either directly or
              through its sources.

       <P><DT><CODE> don't know how to make X </CODE> <DD>

              A target is not present and no actions have been
              defined to create it.

       <P><DT><CODE> X skipped for lack of Y </CODE> <DD>

              A source failed to build, and thus a target cannot
              be built.

       <P><DT><CODE> warning: using independent target X </CODE> <DD>

              A target that is not a dependency of any other
              target is being referenced with $(&lt;) or $(&gt;).

       <P><DT><CODE> X removed </CODE> <DD>

              <b>Jam</b>  removed a  partially built target after being
              interrupted.

	</DL></TABLE>

<DT> <P> <H2> BUGS, LIMITATIONS </H2> <DD>

	<P>

	The -j flag can cause <B>jam</B> to get confused when single
	actions update more than one target at a time. <B>jam</B> may
	proceed as if the targets were built even though they are still
	under construction.

	<P>

	For parallel building to be successful, the dependencies among
	files must be properly spelled out, as targets tend to get built
	in a quickest-first ordering.  Also, beware of un-parallelizable
	commands that drop fixed-named files into the current directory,
	like <b>yacc</b>(1) does.

	<P>

	With the -j flag, errors from failed commands can get staggeringly
	mixed up.  

	<P>

	A poorly set $(JAMSHELL) is likely to result in silent failure.

<DT> <P> <H2> SEE ALSO </H2> <DD>

	<P>

	<UL>

	<LI> <a href="Jambase.html">Jambase Reference</a>

	<LI> <a href="Jamfile.html">Using Jamfiles and Jambase</a>

	</UL>

	<P>

	Jam documentation and source are available from the <A
	HREF="http://public.perforce.com/public/index.html">Perforce
	Public Depot</a>.

<DT> <P> <H2> AUTHOR </H2>   <DD>

	<P>
	Jam's author is Christopher Seiwald (<a 
	href="mailto:seiwald@perforce.com">seiwald@perforce.com</A>).
	Documentation is provided by 
	<A HREF="http://www.perforce.com">Perforce Software, Inc.</A>

</DL>

<P> <HR>   

	<P>

        Copyright 1993-2002 Christopher Seiwald and Perforce Software, Inc.
        <BR>
        Comments to <A HREF="mailto:info@perforce.com">info@perforce.com</A>
        <BR>
        Last updated: May, 2002
	<BR>
	$Id: //public/jam/src/Jam.html#19 $

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