Linux sed 提取数字组
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sed extracting group of digits
提问by Usman
I have tried to extract a number as given below but nothing is printed on screen:
我试图提取下面给出的数字，但屏幕上没有打印任何内容：
echo "This is an example: 65 apples" | sed -n 's/.*\([0-9]*\) apples//p'
However, I get '65', if both digits are matched separately as given below:
但是，如果两个数字分别匹配，我得到“65”，如下所示：
echo "This is an example: 65 apples" | sed -n 's/.*\([0-9][0-9]\) apples//p'
65
How can I match a number such that I don't know the number of digits in a number to be extracted e.g. it can be 2344 in place of 65?
如何匹配一个数字，以至于我不知道要提取的数字的位数，例如它可以是 2344 代替 65？
采纳答案by codaddict
$ echo "This is an example: 65 apples" | sed -r 's/^[^0-9]*([0-9]+).*//'
65
回答by FatalError
What you are seeing is the greedy behavior of regex. In your first example, .*gobbles up all the digits. Something like this does it:
您所看到的是正则表达式的贪婪行为。在您的第一个示例中，.*吞噬了所有数字。像这样的事情：
echo "This is an example: 65144 apples" | sed -n 's/[^0-9]*\([0-9]\+\) apples//p'
65144
This way, you can't match any digits in the first bit. Some regex dialects have a way to ask for non-greedy matching, but I don't believe sedhas one.
这样，您就无法匹配第一位中的任何数字。一些正则表达式方言有一种方法可以要求非贪婪匹配，但我认为没有sed。
回答by mathematical.coffee
It's because your first .*is greedy, and your [0-9]*allows 0 or more digits.
Hence the .*gobbles up as much as it can (including the digits) and the [0-9]*matches nothing.
这是因为您的第一个.*是greedy，并且您[0-9]*允许 0 个或多个数字。因此.*，尽可能多地吞噬（包括数字）并且不[0-9]*匹配。
You can do:
你可以做：
echo "This is an example: 65 apples" | sed -n 's/.*\b\([0-9]\+\) apples//p'
where I forced the [0-9]to match at least one digit, and also added a word boundary before the digits so the whole number is matched.
我强制[0-9]匹配至少一位数字，并在数字前添加了一个单词边界，以便匹配整个数字。
However, it's easier to use grep, where you match just the number:
但是，它更易于使用grep，您只需匹配数字：
echo "This is an example: 65 apples" | grep -P -o '[0-9]+(?= +apples)'
The -Pmeans "perl regex" (so I don't have to worry about escaping the '+').
的-P意思是“Perl的正则表达式”（所以我没有约逃避“+”的担心）。
The -omeans "only print the matches".
的-o意思是“只打印匹配”。
The (?= +apples)means match the digits followed by the word apples.
该(?= +apples)方法相匹配的数字，后跟字苹果。
回答by ctrl-alt-delor
echo "This is an example: 65 apples" | ssed -nR -e 's/.*?\b([0-9]*) apples//p'
You will however need super-sed for this to work. The -R allows perl regexp.
但是，您需要使用 super-sed 才能使其正常工作。-R 允许 perl regexp。
回答by Khate
A simple way for extracting all numbers from a string
从字符串中提取所有数字的简单方法
echo "1213 test 456 test 789" | grep -P -o "\d+"
And the result:
结果：
1213
456
789
