正则表达式从后面匹配字符串

Question

Let's say we have a string "text\t1\nText that has to be extracted" what regex can be used so that we check the string from the back that is from the last " to n because the start of the string can change. In this case, I need to get only Text that has to be extracted . What generic regex can we use here?

I used this (?<=\\n1\\n)(.*)(?=“) but this will not work if the pattern before n changes to n2 or ntext .

Any help is appreciated.

Answer 1

You may use this regex:

/(?<=\\n)[^"\\]+(?="$)/

RegEx Demo

RegEx Details:

• (?<=\\n) : Lookbehind to make sure we have a \n before the current position
• [^"\\]+ : Match 1+ of any character that is not " and not \
• (?="$) : Make sure we have a " before line end ahead

Answer 2

Can't you just split and take the last element?

 var item = "text\n1\nText that has to be extracted"; var last = item.split(/\n/g).reverse()[0]; console.log(last) // "Text that has to be extracted"

Answer 3

/^(\d+)\n([^\n"]+)"$/ may have some edge cases, but will find the number (one or more digits), followed by a newline, followed by any character that is neither newline nor a double quote, followed by a literal double quote.

This would require that the double quote occurs immediately before the end-of-line (EOL), but if that's not required (for example, if you have a semi-colon after the closing quote), remove $ from the end.

Edit

Just noticed that it's the literal text \n and not a newline character.

/(?<=\\n)(\d+)\\n((?:[^\\"]+|\\.)*)"/

Regex101 example

Breakdown:

• (?<=\\n) looks for a \ followed by the letter n .
• (\d+) captures the 1-or-more digits.
• \\n matches a literal \ followed by the letter n .
• (...*) matches some text that repeats 0 or more times.
• (?:...|...) matches any character that are neither a literal \ character nor a double quote character... OR a literal \ character that is followed by "anything" so you can have \n or \" etc. The entire group is matched repeatedly.
• " at the end ensures that you're inside (well, we hope) a double-quoted string on the same line.