Makefile If-Then Else and Loops
MakefileMakefile Problem Overview
Can someone explain how to use if-then statements and for loops in Makefiles? I can't seem to find any good documentation with examples.
Makefile Solutions
Solution 1 - Makefile
Conditional Forms
Simple
conditional-directive
text-if-true
endif
Moderately Complex
conditional-directive
text-if-true
else
text-if-false
endif
More Complex
conditional-directive
text-if-one-is-true
else
conditional-directive
text-if-true
else
text-if-false
endif
endif
Conditional Directives
If Equal Syntax
ifeq (arg1, arg2)
ifeq 'arg1' 'arg2'
ifeq "arg1" "arg2"
ifeq "arg1" 'arg2'
ifeq 'arg1' "arg2"
If Not Equal Syntax
ifneq (arg1, arg2)
ifneq 'arg1' 'arg2'
ifneq "arg1" "arg2"
ifneq "arg1" 'arg2'
ifneq 'arg1' "arg2"
If Defined Syntax
ifdef variable-name
If Not Defined Syntax
ifndef variable-name
foreach Function
foreach Function Syntax
$(foreach var, list, text)
foreach Semantics
For each whitespace separated word in "list", the variable named by "var" is set to that word and text is executed.
Solution 2 - Makefile
Here's an example if:
ifeq ($(strip $(OS)),Linux)
PYTHON = /usr/bin/python
FIND = /usr/bin/find
endif
Note that this comes with a word of warning that different versions of Make have slightly different syntax, none of which seems to be documented very well.
Solution 3 - Makefile
Have you tried the GNU make documentation? It has a whole section about conditionals with examples.
Solution 4 - Makefile
You do see for loops alot of the time, but they are usually not needed. Here is an example of how one might perform a for loop without resorting to the shell
LIST_OF_THINGS_TO_DO = do_this do_that
$(LIST_OF_THINGS_TO_DO):
run $@ > $@.out
SUBDIRS = snafu fubar
$(SUBDIRS):
cd $@ && $(MAKE)