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Pitfalls of Using Wildcards
Now here is an example of a naive way of using wildcard expansion,
that does not do what you would intend. Suppose you would like to say
that the executable file `foo' is made from all the object files in the
directory, and you write this:
objects = *.o
foo : $(objects)
cc -o foo $(CFLAGS) $(objects)
The value of `objects' is the actual string `*.o'. Wildcard expansion
happens in the rule for `foo', so that each *existing* `.o' file
becomes a dependency of `foo' and will be recompiled if necessary.
But what if you delete all the `.o' files? When a wildcard matches
no files, it is left as it is, so then `foo' will depend on the
oddly-named file `*.o'. Since no such file is likely to exist, `make'
will give you an error saying it cannot figure out how to make `*.o'.
This is not what you want!
Actually it is possible to obtain the desired result with wildcard
expansion, but you need more sophisticated techniques, including the
`wildcard' function and string substitution. Note: The Function
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