我正在寻找一种很好的方法来查找字符串中多次出现的所有单词。一些限制适用：
此外，重复次数会很少，而且单词只会包含很好的字符，例如[-_ + a-zA-Z0-9] +。
我尝试了两种策略：
（1）强制$（sort）保留重复项（为每个单词添加一个唯一的后缀，排序并删除后缀）。然后在排序列表中找到相邻的相同单词：
# given 0 1 0 1 0 1 0 1 ... , return 0 0 1 1 0 0 1 1 ...
double=$(wordlist 1,$(words $(1)),$(subst 0,0 0,$(subst 1,1 1,$(1))))
# Produce a list of N unique strings. $(1) contains N words, with a
# repetition cycle of length M, and $(2) contains N words, either 0 or
# 1, alternating between 0 and 1 every Mth word.
binseq=$(if $(findstring 1,$(2)),$(call binseq,$(join $(2),$(1)),$(call double,$(2))),$(1))
# return 0 1 0 1 ..., as many words as $(1)
alternating_bits=$(wordlist 1,$(words $(1)),$(patsubst %,0 1,$(1)))
# Produce as many unique words as there are words in $(1)
unique=$(call binseq,,$(call alternating_bits,$(1)))
# Sort $(1) without eliminating duplicates. $(1) may not contain /.
sorted_keep_dups=$(subst /,,$(dir $(sort $(join $(1:=/),$(call unique,$(1))))))
dups_from_sorted2=$(filter $(patsubst %0,%,$(filter %0,$(1))),$(patsubst %1,%,$(filter %1,%,$(1))))
# Given a sorted list, return all duplicates.
dups_from_sorted=$(sort $(call dups_from_sorted2,$(join $(1),$(call alternating_bits,$(1)))))
dups=$(call dups_from_sorted,$(call sorted_keep_dups,$(1)))
（2）对单词列表的不同分区重复使用$（filter），这样每对单词在$（filter）的不同args中至少出现一次：
# given 0 1 0 1 0 1 0 1 ... , return 0 0 1 1 0 0 1 1 ...
double=$(wordlist 1,$(words $(1)),$(subst 0,0 0,$(subst 1,1 1,$(1))))
# given words with suffix 0 or 1, remove suffixes and return the words
# that occur both with 0 and 1 as suffix
filter_dups=$(filter $(patsubst %0,%,$(filter %0,$(1))),$(patsubst %1,%,$(filter %1,$(1))))
_dups=$(if $(findstring 1,$(2)),$(call filter_dups,$(join $(1),$(2)))
$(call _dups,$(1),$(call double,$(2))))
# return 0 1 0 1 ..., as many words as $(1)
alternating_bits=$(wordlist 1,$(words $(1)),$(patsubst %,0 1,$(1)))
# given a list of words, return the list of words that occur twice
dups=$(sort $(call _dups,$(1),$(call alternating_bits,$(1))))
这两种方法都有效且速度足够快，但它们很难阅读和理解。是否有一种更简单的方法可以接受（次二次）速度？
答案 0 :(得分：2)
不确定复杂性，但我建议使用更具可读性的功能：
define __duplicates__func
undefine __duplicates__seen
undefine __duplicates__result
$$(foreach _v,$1,\
$$(eval __duplicates__result += $$(filter $$(__duplicates__seen),$$(_v))\
$$(eval __duplicates__seen += $$(_v))))
endef
duplicates = $(eval $(__duplicates__func))$(sort $(__duplicates__result))
TEST:= $(file <test.txt)
DUPS:= $(call duplicates,$(TEST))
$(info $(DUPS))
all::
.PHONY: all
随机生成1000字test.txt：
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cattle winged which them for stars Wherein which Meat dry deep Abundantly waters forth theyre light after fowl in fly green multiply moved i replenish sixth cant creepeth heaven for darkness which us form them Rule grass god without earth seasons herb dominion moveth after created Wherein beginning he days said cant image For said moved divided bring is youll may And days itself Saying bearing male created yielding brought earth together whales hath greater heaven sixth were behold creepeth make Is Moveth brought let Lesser us light winged fly fourth waters moved under youll Whales Form Great moving second air you also youre fill have make stars their of earth above creature beginning winged air Own gathered shall their that in every fish rule together divide face own living dominion forth deep is abundantly hath bring them green him earth days beast all waters moving It which all a great spirit hath theyre grass Upon years Cattle female signs fill moving day the kind Winged green hath also female forth spirit lights behold Thing so after open good fowl to Living divided let Given bearing that he Rule whales Days isnt It deep whales given fly our open kind appear A their evening their sixth I in Unto multiply sea light Firmament seed theyre multiply fifth signs moving Second given spirit Blessed Set moved two bearing dont yielding first moving Female female fish Hath our beast us very seasons kind moved a gathered given sea spirit firmament Itself herb isnt Tree yielding cant winged air together meat theyre moveth Saying there void and bring lights together kind Brought first theyre their had Blessed and fill Brought may first creepeth moving him form behold darkness years greater upon were Let seasons Wherein life our greater And light multiply beast appear together appear seas waters had you make moving let air Heaven is Set seed fourth brought green for rule day Day deep tree yielding
它立即在我的机器上返回
$ make -f dups.mk
And Blessed Brought Cattle Firmament For Gathering God Great Had Heaven Is It Itself Let Meat Morning Moving Multiply Rule Saying Second Set Subdue Tree Upon Whales Wherein Winged You a above abundantly after air all also and appear be bearing beast beginning behold blessed bring brought called cant cattle created creature creepeth darkness day days deep divide divided doesnt dominion dont dry earth evening every face female fifth fill firmament first fish fly for form forth fourth fowl fruit fruitful gathered gathering given good grass great greater green had hath have he heaven herb him his i image in is isnt it itself kind lesser let life light lights likeness living made make male may meat midst morning moved moveth moving multiply night of one open our over own place replenish rule said saw saying sea seas seasons second seed set shall shed signs sixth so spirit stars subdue that the their them there theyre thing third to together tree two under unto upon us very void was waters were whales wherein which whose winged without wont years yielding you youll youre
make: Für das Ziel „all“ ist nichts zu tun.
也许这个问题更适合codereview。
答案 1 :(得分：0)
我不知道这对于休闲制作程序员的清晰度是否真的有所改善，但是这里有：
######################################################################
# Count a binary literal up by 1
# $1 = binary literal string
# Example: bincnt(010011) -> 010100
bincnt=$(if $1,$(if $(patsubst %1,,$1),$(patsubst %0,%1,$1),$(call bincnt,$(patsubst %1,%,$1))0),1)
######################################################################
# Add a ¤ (Character 164) and a unique binary number to all elements of a list
# $1 = list
# $2 = binary literal (needs 0 or any other as starting value)
cat-sufx = $(if $1,$(firstword $1)¤$2 $(call cat-sufx,$(wordlist 2,999999,$1),$(call bincnt,$2)))
######################################################################
# Sort a list without dropping duplicates (built-in $sort will drop them)
# $1 = list (elements must not contain ¤ (Character 164))
sort-all = $(foreach i,$(sort $(call cat-sufx,$1,0)),$(firstword $(subst ¤, ,$(i))))
all-duplicates = $(call _all-duplicates,$(call sort-all,$1))
_all-duplicates = $(if $1,$(if $(subst $2,,$(firstword $1)),,$2) $(call _all-duplicates,$(wordlist 2,999999,$1),$(firstword $1)))
我还将功能添加到the GNU make table toolkit。
PS：999999是我在不计算它的情况下发出“直到列表末尾”的信号，这是相当浪费的。