问题
I want to build a regex where it searches for a string containing 12 digits in a row. If there's no match, look for a string with only 10 digits in a row.
For example:
a123456789012a
a1234567890a
Would return:
123456789012
And if the input is:
a1234a
a1234567890a
It would return:
1234567890
I managed to create the regex for the individual operations, beeing (?<!\d)\d{10}(?!\d) for 10 digits and (?<!\d)\d{12}(?!\d) for 12 digits, but I can't group them up in a if-else style.
I tried the following:
(?(?<!\d)\d{12}(?!\d)|((?<!\d)\d{10}(?!\d)))
but if the first pattern don't match, the regex don't try to match the second, returning nothing
回答1:
You can use a simple regex like this:
\d{12}|\d{10}
working demo
Look that I have not used multiline nor global flags. This way the pattern is going to find the first match you want.
Case 1:
Case 2:
BTW, use capturing groups if you want to capture the content:
(\d{12}|\d{10})
来源：https://stackoverflow.com/questions/57698986/if-else-regex-matching