File: make.info,  Node: Static Usage,  Next: Static versus Implicit,  Prev: Static_Pattern.php">Static Pattern,  Up: Static_Pattern.php">Static Pattern

4.12.1 Syntax of Static Pattern Rules
-------------------------------------

Here is the syntax of a static pattern rule:

     TARGETS ...: TARGET-PATTERN: PREREQ-PATTERNS ...
             RECIPE
             ...

The TARGETS list specifies the targets that the rule applies to.  The
targets can contain wildcard characters, just like the targets of
ordinary rules (*note Using Wildcard Characters in File Names:
Wildcards.).

   The TARGET-PATTERN and PREREQ-PATTERNS say how to compute the
prerequisites of each target.  Each target is matched against the
TARGET-PATTERN to extract a part of the target name, called the "stem".
This stem is substituted into each of the PREREQ-PATTERNS to make the
prerequisite names (one from each PREREQ-PATTERN).

   Each pattern normally contains the character '%' just once.  When the
TARGET-PATTERN matches a target, the '%' can match any part of the
target name; this part is called the "stem".  The rest of the pattern
must match exactly.  For example, the target 'foo.o' matches the pattern
'%.o', with 'foo' as the stem.  The targets 'foo.c' and 'foo.out' do not
match that pattern.

   The prerequisite names for each target are made by substituting the
stem for the '%' in each prerequisite pattern.  For example, if one
prerequisite pattern is '%.c', then substitution of the stem 'foo' gives
the prerequisite name 'foo.c'.  It is legitimate to write a prerequisite
pattern that does not contain '%'; then this prerequisite is the same
for all targets.

   '%' characters in pattern rules can be quoted with preceding
backslashes ('\').  Backslashes that would otherwise quote '%'
characters can be quoted with more backslashes.  Backslashes that quote
'%' characters or other backslashes are removed from the pattern before
it is compared to file names or has a stem substituted into it.
Backslashes that are not in danger of quoting '%' characters go
unmolested.  For example, the pattern 'the\%weird\\%pattern\\' has
'the%weird\' preceding the operative '%' character, and 'pattern\\'
following it.  The final two backslashes are left alone because they
cannot affect any '%' character.

   Here is an example, which compiles each of 'foo.o' and 'bar.o' from
the corresponding '.c' file:

     objects = foo.o bar.o

     all: $(objects)

     $(objects): %.o: %.c
             $(CC) -c $(CFLAGS) $< -o $@

Here '$<' is the automatic variable that holds the name of the
prerequisite and '$@' is the automatic variable that holds the name of
the target; see *note Automatic Variables::.

   Each target specified must match the target pattern; a warning is
issued for each target that does not.  If you have a list of files, only
some of which will match the pattern, you can use the 'filter' function
to remove non-matching file names (*note Functions for String
Substitution and Analysis: Text Functions.):

     files = foo.elc bar.o lose.o

     $(filter %.o,$(files)): %.o: %.c
             $(CC) -c $(CFLAGS) $< -o $@
     $(filter %.elc,$(files)): %.elc: %.el
             emacs -f batch-byte-compile $<

In this example the result of '$(filter %.o,$(files))' is 'bar.o
lose.o', and the first static pattern rule causes each of these object
files to be updated by compiling the corresponding C source file.  The
result of '$(filter %.elc,$(files))' is 'foo.elc', so that file is made
from 'foo.el'.

   Another example shows how to use '$*' in static pattern rules:

     bigoutput littleoutput : %output : text.g
             generate text.g -$* > $@

When the 'generate' command is run, '$*' will expand to the stem, either
'big' or 'little'.