Makefile in Linux

                         -----------------------MAKEFILE-----------------------------

A Makefile basically consists of :

1) Definitions of variables and functions,
   example: myshell=bash
2) Commensts:
   e.g. # converting postscript to pdf or what ever
3) Includes:
   e.g.- include Makefile.local
4) Rules:
   e.g. - %.pdf: %.ps; -@ps2pdf $<

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**)Mind the tab key (<tab>) prefacing the commands past the fist line.

**)Use a semicolon to stuff muiltiple commands into one single lin, or a backslash to join split lines. (Refer Makefile1)

NOTE::
I. The at-sign (@) in front of the commnad prevents make from announcing the commands it's going to do.
II. If you don't tell make a target, it will simply do the first rule.
III. If you tell make multiple targets, it will do them all in order.

------------------------------------------------------------------
We can Combine multiple makefiles:

command in makefile(-include m/Makefile-l)

When make encounters an include-command, it will stop processing the current Makefile, read the included Makefile and then continue where it left off.

-----------------------------------------------------------
If we define a target socks twice it will give the warning mesage
Example:
socks: ; @echo get into left sock
socks: ; @echo get inot right sock
***While make it will give the warning messages z`       
***For remove the warning message we have to duplicate the colon:

socks:: ; @echo get into left sock
socks:: ; @echo get inot right sock
*** Now When we make this it will not give the error
Imp Note:

CXXSOURCES = basic_sample.cpp       # list of source files
CXXOBJECTS = $(CXXSOURCES:.cpp=.o)  # expands to list of object files


-----------------------------------Built-in fuctions------------------------------
1) $(subst from,to,text)     Replace from with to in text.
2) $(patsubst pattern,replacement,text)  Replace words matching pattern with replacement in text.
3) $(strip string) Remove excess whitespace characters from string.
4) $(findstring find,text)     Locate find in text.
5) $(filter pattern...,text)     Select words in text that match one of the pattern words.
6) $(filter-out pattern...,text)     Select words in text that do not match any of the pattern words.
7) $(sort list)     Sort the words in list lexicographically, removing duplicates.
8) $(dir names...)     Extract the directory part of each file name.
9) $(notdir names...)     Extract the non-directory part of each file name.
10) $(suffix names...)     Extract the suffix (the last dot and following characters) of each file name.
11) $(basename names...)     Extract the base name (name without suffix) of each file name.
12) $(addsuffix suffix,names...)     Append suffix to each word in names.
13) $(addprefix prefix,names...)     Prepend prefix to each word in names.
14) $(join list1,list2)     Join two parallel lists of words.
15) $(word n,text)     Extract the nth word (one-origin) of text.
16) $(words text)     Count the number of words in text.
17) $(wordlist s,e,text)     Returns the list of words in text from s to e.
18) $(firstword names...)     Extract the first word of names.
19) $(wildcard pattern...)     Find file names matching a shell file name pattern (not a `%' pattern).
20) $(error text...)     When this function is evaluated, make generates a fatal error with the message text.
21) $(warning text...)     When this function is evaluated, make generates a warning with the message text.
22) $(shell command)     Execute a shell command and return its output.
23) $(origin variable)     Return a string describing how the make variable variable was defined.
24) $(foreach var,words,text)     Evaluate text with var bound to each word in words, and concatenate the results.
25) $(call var,param,...)     Evaluate the variable var replacing any references to $(1),$(2) with the first, second, etc. param values.


-----------------------------------Automatic Variable----------------------------------

$@     The name of the target.
$%     The target member name, when the target is an archive member.
$<     The name of the first (or only) prerequisite.
$?     The names of all the prerequisites that are newer than the target, with spaces between them.

$^ $+   The names of all the prerequisites, with spaces between them. The value of $^ omits duplicate prerequisites, while $+ retains them and preserves their order.
$*     The stem with which an implicit rule matches.
$(@D)
$(@F)     The directory part and the file-within-directory part of $@

$(*D)
$(*F)     The directory part and the file-within-directory part of $*

$(%D)
$(%F)     The directory part and the file-within-directory part of $%

$(<D)
$(<F)     The directory part and the file-within-directory part of $<

$(^D)
$(^F)     The directory part and the file-within-directory part of $^

$(+D)
$(+F)     The directory part and the file-within-directory part of $+

$(?D)
$(?F)     The directory part and the file-within-directory part of $?