使用bash计算字符串中子字符串的出现次数(count no of occurences of a substring in a string using bash)

使用bash计算字符串中子字符串的出现次数(count no of occurences of a substring in a string using bash)

计数为2时，模式在字符串中出现三次

echo "axxxaaxx" | grep -o "xx" | wc -l echo "axxxaaxx" | grep -o "xx"

It is giving count as 2 where as pattern occurred thrice in the string

echo "axxxaaxx" | grep -o "xx" | wc -l echo "axxxaaxx" | grep -o "xx"

最满意答案

使用-P将启用支持外观的 PCRE：

echo "axxxaaxx" | grep -P '(?<=x)x'

在这种情况下，我们使用lookbehind，这意味着我们将匹配在它之前有x 。 这使我们能够重叠匹配：

如何“评估”正则表达式：

xxx ^^ |Cursor Looking for x on this position, since there is nothing this will not match xxx ^^ |Cursor Looking for x on this position since it's found we got a match xxx ^^ |Cursor Looking for x on this position since it's found we got a match

Using -P will enable PCRE which supports lookarounds:

echo "axxxaaxx" | grep -P '(?<=x)x'

In this case we are using a lookbehind which means that we will match an x which have an x before it. This makes us able to have overlapping matches:

How the regex is "evaluated":

xxx ^^ |Cursor Looking for x on this position, since there is nothing this will not match xxx ^^ |Cursor Looking for x on this position since it's found we got a match xxx ^^ |Cursor Looking for x on this position since it's found we got a match