Why does GREP expression need two back-slashes?

Question

Hi, there.Curious question:I have the following code:   psYSbody.nestedGrepStyles.add({        appliedCharacterStyle: csYSimporedPsukimMekor,        grepExpression: "$.+?$"});Why does this only work if I have double-backslashes before "()" and "[]"?If I only have a single backslash it will totally ignore the backslash.Anyone could explain this quirk?

Trevor: · Accepted Answer

HiThe "/" character is an escape character. For example if you want to alert "the "big" cat" with the word cat in quotes one way of doing it is alert("the "big" cat");Because you are providing a string you need to escape the escapeTry the following 2 examplesalert("\(") // => (alert("\(") // => \(What you want is the second example as the "correct" grep is \( and not (Got it?Trevor

Marc Autret · Answer

Hi,Another way to explain the double-escape trick is to consider those two distinct levels:1. At the GREP (or regular expression) level, parentheses ( and ) are special symbols that control capturing groups.So if you want to capture a left parenthesis as itself you need to use an escape sequence.In GREP, the escape character is \ (backslash) so that the full escape sequence is \( (backslash + parenthesis.)2. At the JavaScript level (which is the language you are using to send the above GREP command), the backslash \ is a special symbol when involved in a literal string. Indeed, that symbol is used to form escape sequences!So if you want to provide the backslash as itself in a literal string, you need the following escape sequence, "\" (backslash + backslash), which in fact represents a single backslash character.Finally, in order to encode in JavaScript the full GREP pattern \( —that is, a backslash and a left parenthesis—you'll have to use the literal string "\(".[The reasoning is the same for square brackets.]Hope that helps.@+Marc

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