如何使用 Bash 从一组字符串 B 中过滤出一组字符串 A
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How to filter out a set of strings A from a set of strings B using Bash
提问by Ilyes Gouta
I have a list of strings which I want to remove from a super set of another strings, not in a any specific order and thus constructing a new set. Is that doable in Bash?
我有一个字符串列表，我想从另一个字符串的超集中删除它，而不是按照任何特定的顺序，从而构建一个新的集合。这在 Bash 中可行吗？
回答by Evan Krall
It looks like you're looking for something with better than O(nm) running time, so here's an answer to that. Fgrep or grep -F uses the Aho-Corasick algorithm to make a single FSM out of a list of fixed strings, so checking each word in SET2 takes O(length of word) time. This means the whole running time of this script is O(n+m).
看起来您正在寻找比 O(nm) 运行时间更好的东西，所以这里有一个答案。Fgrep 或 grep -F 使用 Aho-Corasick 算法从固定字符串列表中生成单个 FSM，因此检查 SET2 中的每个单词需要 O（单词长度）时间。这意味着这个脚本的整个运行时间是 O(n+m)。
(obviously the running times are also dependent on the length of the words)
（显然运行时间也取决于单词的长度）
[meatmanek@yggdrasil ~]$ cat subtract.sh
#!/bin/bash
subtract()
{
SET1=( )
SET2=( )
OLDIFS="$IFS"
IFS=$'\n'
SET3=( $(grep -Fxv "${SET1[*]}" <<< "${SET2[*]}") )
IFS="$OLDIFS"
echo "${SET3[*]}"
# SET3 = SET2-SET1
}
subtract "$@"
[meatmanek@yggdrasil ~]$ . subtract.sh
[meatmanek@yggdrasil ~]$ subtract "package-x86 test0 hello world" "computer hello sizeof compiler world package-x86 rocks"
computer sizeof compiler rocks
[meatmanek@yggdrasil ~]$
回答by Adam Bard
I think you'll have to at least characterize the parameters of the subset of strings you want to extract. If it's textfield-like data, though, look into awk.
我认为您至少必须描述要提取的字符串子集的参数。但是，如果它是类似文本字段的数据，请查看 awk。
回答by Andreas Otto
> echo "aa b1 c b2 d" |xargs -d' ' -n 1
aa
b1
c
b2
d
> echo "aa b1 c b2 d" |xargs -d' ' -n 1| grep "^b"
b1
b2
回答by Chris Johnsen
How about any ugly abuse of the builtin command hash?
对内置命令的任何丑陋滥用怎么样hash？
#!/bin/bash
set -eu
filter_out() {
local words="" words_to_remove=""
( # do this in a subshell to avoid contaminating the main script
set +e
hash -r
hash -p bogus-placeholder $words
hash -d $words_to_remove > /dev/null 2>&1
left=''
for word in $words; do
hash -t "$word" > /dev/null 2>&1 && left="${left}${left:+ }$word"
done
printf '%s\n' "$left"
)
}
filter_out "package-x86 test0 hello world" "computer hello sizeof compiler world package-x86 rocks test0"
w='foo bar baz quux toto'
d='baz toto quux'
filter_out "$d" "$w"
回答by ghostdog74
#!/bin/bash
SET1="package-x86 test0 hello world"
SET2="computer hello sizeof compiler world package-x86 rocks test0"
awk -v s1="$SET1" -v s2="$SET2" 'BEGIN{
m=split(s1,set1)
n=split(s2,set2)
for(i=1;i<=n;i++){
for (j=1;j<=m;j++){
if ( set1[j] == set2[i]){
delete set2[i]
}
}
}
for(i in set2) if (set2[i]!="") {print set2[i]}
}'
output
输出
# ./shell.sh
compiler
rocks
computer
sizeof
回答by Paused until further notice.
This is, what, O(n) or O(n+m)?
这是，什么，O(n) 还是 O(n+m)？
#!/bin/bash
SET1="package-x86 test0 hello world"
SET2="computer hello sizeof compiler world package-x86 rocks test0"
for i in $SET2
do
[[ ! $SET1 =~ $i ]] && SET3="${SET3:+${SET3} }$i"
done
echo "..${SET3}.."
Running it:
运行它：
$ ./script
..computer sizeof compiler rocks..
回答by Idelic
Without using anything bash-specific or external commands:
不使用任何 bash 特定或外部命令：
SET1="package-x86 test0 hello world"
SET2="computer hello sizeof compiler world package-x86 rocks test0"
SET3=
for arg in $SET2; do
case $SET1 in
$arg\ * | *\ $arg | *\ $arg\ *) ;;
*) SET3="$SET3 $arg" ;;
esac
done
回答by Vinko Vrsalovic
This uses grep to see if a word has to be removed, but that's not pure BASH and it's probably faster than the other option (see below)
这使用 grep 来查看是否必须删除某个单词，但这不是纯 BASH 并且它可能比其他选项更快（见下文）
#!/bin/bash
REMOVE="package-x86 test0 hello world"
WORDBAG="computer hello sizeof compiler world package-x86 rocks test0"
OFS=$IFS
IFS=" "
WORDBAG_ARRAY=($WORDBAG)
IFS=$OFS
RESULT=""
for str2 in ${WORDBAG_ARRAY[@]}
do
echo $REMOVE | grep $str2 >/dev/null
if [[ $? == 1 ]] #Not Found
then
RESULT="$RESULT $str2"
fi
done
echo $RESULT
This is a bit verbose, uses BASH arrays, and is O(N*M), but works.
这有点冗长，使用 BASH 数组，并且是 O(N*M)，但有效。
#!/bin/bash
REMOVE="package-x86 test0 hello world"
WORDBAG="computer hello sizeof compiler world package-x86 rocks test0"
OFS=$IFS
IFS=" "
REMOVE_ARRAY=($REMOVE)
WORDBAG_ARRAY=($WORDBAG)
IFS=$OFS
RESULT=""
for str2 in ${WORDBAG_ARRAY[@]}
do
found=0
for str1 in ${REMOVE_ARRAY[@]}
do
if [[ "$str1" == "$str2" ]]
then
found=1
fi
done
if [[ $found == 0 ]]
then
RESULT="$RESULT $str2"
fi
done
echo $RESULT
