Using Regex with Kotlin

Question

According to http://www.regexplanet.com/advanced/java/index.html, my regex

\\uline\{[a-zA-Z\d]+\}|\\text(super|sub)script\{[0-9]+.[0-9]+\}

should work fine to detect e.g. 1) \textsuperscript{1.1} and 2) \uline{name}

Furthermore, replaceFirst works as expected: 12345\textsuperscript{1.1}6789 goes to 123456789

I doubled backslashes and added the regex to my Kotlin code (in IntelliJ Idea):

var stylingRegex = "\\\\uline\\{[a-zA-Z\\d]+\\}|\\\\text(super|sub)script    \\{[0-9]+.[0-9]+\\}"
var testString = "12345\\uline{james}678"
testString = testString.replaceFirst(Pattern.quote(stylingRegex), "")
println("testString: " + testString)

However, what's printed is the initialized string without any modification.

You should not quote the regex, remove Pattern.quote(), use testString = testString.replaceFirst(stylingRegex.toRegex(), "") — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Mar 19, 2018 at 11:03
Here is a demo showing that Wiktor's suggestion fixes the problem. — Tim Biegeleisen
– Tim Biegeleisen, Commented Mar 19, 2018 at 11:04

Wiktor Stribiżew · Accepted Answer · 2018-03-19 11:06:17Z

4

You should not quote the regex pattern and you should make sure you pass a regex to the replaceFirst:

testString = testString.replaceFirst(stylingRegex.toRegex(), "")

See the online Kotlin demo:

var stylingRegex = """\\uline\{[a-zA-Z\d]+\}|\\text(super|sub)script\{[0-9]+\.[0-9]+\}"""
var testString = "12345\\uline{james}678"
testString = testString.replaceFirst(stylingRegex.toRegex(), "")
println("testString: " + testString)
// => testString: 12345678

Note that you do not need to use excessive backslashes when using raw string literals (defined with """...""""), inside them, the \ symbol denotes a literal backslash that is used to create regex escapes.

Also, to match float numbers only, you need to escape the dot in the [0-9]+.[0-9]+ part of your pattern. To match both integer and float, use [0-9]+(?:\.[0-9]+)?.

answered Mar 19, 2018 at 11:06

Wiktor Stribiżew

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