正则表达式将 substring 放在字符串中特殊字符的左侧

Question

I have certain expressions that looks like this

"sum='29'"

'The total score =" 29"'

"Your name = 'John'"

"Your grade is A"

Now what I want to do is to check if the left side of quote ( ' or " ) contains an = .

So this is what I do

leftTermOfQuote = string.match(/\S+(?' *')/)[0]

But I get null . What am I doing wrong?

Answer 1

To get the left side of a ' or " , you could capture the first part in a group while matching the first ' or "

To not cross the quotes or = boundary, you could use a negated character class [^'"\r\n=] matching any char except the listed.

^([^'"\r\n=]*=[^'"\r\n=]*)['"]

Explanation

• ^ Start of string
• ( Capture group 1
  • [^'"\r\n=]* Match any char except the quotes, equals sign or newline
  • = Match the equals sign
  • [^'"\r\n=]* Same as previous character class
• ) Close group
• ['"] Match a ' or "

Regex demo

 [ `sum='29'`, `The total score =" 29"`, `Your name = 'John'`, `Your grade is A` ].forEach(s => { let res = s.match(/^([^'"\r\n=]*=[^'"\r\n=]*)['"]/); if (res) { console.log(res[1]); } })

Answer 2

Now what I want to do is to check if the left side of quote (' or ") contains an =.

You can do that by searching for =.*['"] . But this would also find The result is 'A=B' because =B' matches the requirements.

So you can anchor the regex to the first character and request that before the first quote, there is an equal sign:

^[^'"]*=[^'"]*['"]

This reads as: "from the beginning of the string ^, there may be non-quotes [^'"], in any number *, before an equal sign =, followed by any number of non-quotes, finally followed by a quote"

You can also parse the whole assignment:

^([^=]*)\\s*=\\s*"\\s*(.*)\\s*"

this will also extract the parenthesized parts of the assignment, giving you an array with whatever is on the left of the equal sign, and whatever is on the right inside the quotes. It should also remove whitespaces, so

'  The total score     =   "  29"  '

is parsed into

[ "The total score", "29" ]

Answer 3

You can use the split and includes functions as well:

const word = 'The total score =" 29"';
const wordSplitByQuotes = word.split(/"(?:[^"\\]|\\.)*"|'(?:[^'\\]|\\.)*'/);
const containsEqualSign = wordSplitByQuotes[0].includes('=');