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Chapter 8: Functions for Transforming Text 87

produces the result ‘bar’. Although $(lastword text) is the same as $(word

$(words text),text), the lastword function was added for its simplicity and

better performance.

Here is a realistic example of the use of subst and patsubst. Suppose that a makeﬁle

uses the VPATH variable to specify a list of directories that make should search for prerequisite

ﬁles (see Section 4.4.1 [VPATH Search Path for All Prerequisites], page 25). This example

shows how to tell the C compiler to search for header ﬁles in the same list of directories.

The value of VPATH is a list of directories separated by colons, such as ‘src:../headers’.

First, the subst function is used to change the colons to spaces:

$(subst :, ,$(VPATH))

This produces ‘src ../headers’. Then patsubst is used to turn each directory name

into a ‘-I’ ﬂag. These can be added to the value of the variable CFLAGS, which is passed

automatically to the C compiler, like this:

override CFLAGS += $(patsubst %,-I%,$(subst :, ,$(VPATH)))

The eﬀect is to append the text ‘-Isrc -I../headers’ to the previously given value of

CFLAGS. The override directive is used so that the new value is assigned even if the

previous value of CFLAGS was speciﬁed with a command argument (see

Section 6.7 [The

override Directive], page 68).

8.3 Functions for File Names

Several of the built-in expansion functions relate speciﬁcally to taking apart ﬁle names or

lists of ﬁle names.

Each of the following functions performs a speciﬁc transformation on a ﬁle name. The

argument of the function is regarded as a series of ﬁle names, separated by whitespace.

(Leading and trailing whitespace is ignored.) Each ﬁle name in the series is transformed in

the same way and the results are concatenated with single spaces between them.

$(dir names...)

Extracts the directory-part of each ﬁle name in names. The directory-part of

the ﬁle name is everything up through (and including) the last slash in it. If the

ﬁle name contains no slash, the directory part is the string ‘./’. For example,

$(dir src/foo.c hacks)

produces the result ‘src/ ./’.

$(notdir names...)

Extracts all but the directory-part of each ﬁle name in names. If the ﬁle name

contains no slash, it is left unchanged. Otherwise, everything through the last

slash is removed from it.

A ﬁle name that ends with a slash becomes an empty string. This is unfortunate,

because it means that the result does not always have the same number of

whitespace-separated ﬁle names as the argument had; but we do not see any

other valid alternative.

For example,

$(notdir src/foo.c hacks)

produces the result ‘foo.c hacks’.

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