Makefile 文本处理函数（下）

sort函数：单词排序

$(sort LIST)

sort函数对字符串LIST中的单词以首字母为准进行排序，并删除重复的单词。

.PHONY: all
FILE = a.c b.h c.s d.cpp   
SRC = $(filter-out %.c, $(FILE))
all:
    @echo "FILE = $(FILE)"
    @echo "SRC = $(SRC)"

执行make，运行结果为：

# make
LIST = banana pear apple peach apple orange 
STR = apple banana orange peach pear

word函数：取单词

word函数的作用是从一个字符串TEXT中，按照指定的数目N取单词：

 $(word N,TEXT)

函数的返回值是字符串TEXT中的第N个单词。如果N的值大于字符串中单词的个数，返回空；如果N为0，则出错。

.PHONY: all
LIST = banana pear apple peach orange 
word1 = $(word 1, $(LIST))
word2 = $(word 2, $(LIST))
word3 = $(word 3, $(LIST))
word4 = $(word 4, $(LIST))
word5 = $(word 5, $(LIST))
word6 = $(word 6, $(LIST))
all:
    @echo "word1 = $(word1)"
    @echo "word2 = $(word2)"
    @echo "word3 = $(word3)"
    @echo "word4 = $(word4)"
    @echo "word5 = $(word5)"
    @echo "word6 = $(word6)"

执行make，运行结果为：

# make
word1 = banana
word2 = pear
word3 = apple
word4 = peach
word5 = orange
word6 =

如果N的值为0，Makefile含有下面的语句：

word0 = $(word 0, $(LIST))

则会报错：

makefile:9: *** first argument to 'word' function must be greater than 0.  Stop.

wordlist函数：取字串

wordlist函数用来从一个字符串TEXT中取出从N到M之间的一个单词串：

$(wordlist N, M, TEXT)

N 和 M都是从1开始的一个数字，函数的返回值是字符串TEXT中从N到M的一个单词串。当N比字符串TEXT中的单词个数大时，函数返回空。

.PHONY: all
LIST = banana pear apple peach orange 
sub_list = $(wordlist 1, 3, $(LIST))
all:
    @echo "LIST = $(LIST)"
    @echo "sub_list = $(sub_list)"

执行make时，wordlist函数会将字符串LIST中的前三个单词赋值给sub_list：

# make
LIST = banana pear apple peach orange 
sub_list = banana pear apple

words函数：统计单词数目

words函数用来统计一个字符串TEXT中单词的个数：

$(words TEXT)

words函数的返回值为字符串TEXT中单词的个数。

.PHONY: all
LIST = banana pear apple peach orange 
all:
    @echo "LIST = $(LIST)"
    @echo "LIST len = $(words $(LIST))

执行make，运行结果为：

# make
LIST = banana pear apple peach orange 
LIST len = 5

firstword函数：取首个单词

firstword函数用来取一个字符串中的首个单词。

$(firstword NAMES…)
$(word 1,TEXT)

firstword函数其实就相当于$(word 1,TEXT)：

.PHONY: all
LIST = banana pear apple peach orange 
all:
    @echo "LIST = $(LIST)"
    @echo "first word = $(firstword $(LIST))"

执行make，运行结果为：

# make
LIST = banana pear apple peach orange 
first word = banana