Escape all regex metacharacters in a string with backslash in Kotlin

Question

As you probably all know, regular expressions have some metacharacters, such as \, |, ., ?, +, *,…. If you want to search for a substring including one of these characters without actually using the regex behaviour, you can escape it with a backslash.

So if you want to search for "Is it true?" in a string you would use the pattern "Is it true\?".

I am using Kotlin and its built-in regular expressions. Is there a way in Kotlin (a function or something) to get a string from another string in which all of the special characters in the input string are escaped?

So if the input to such a function were "This is good." the output would be "This is good\.", and for "? a [+" it would be "\? a \[\+". → every regex special character in the output is escaped with a backslash.

Are you looking for kotlinlang.org/api/latest/jvm/stdlib/kotlin.text/-regex/…? — Slaw
– Slaw, Commented Dec 25, 2022 at 3:53
Frame challenge: if you want to search for a literal string, why are you using a regex? There are simpler (and more efficient) ways to search for a literal string. — gidds
– gidds, Commented Dec 26, 2022 at 11:51
@gidds Good to raise alternatives, but in general, there is a use case for regex-escaping, as the literal string may well be part of a bigger regex. — Ruud Helderman
– Ruud Helderman, Commented Dec 26, 2022 at 14:35
Yes Regex.escape (kotlinlang.org/api/latest/jvm/stdlib/kotlin.text/-regex/…) is what I was looking for. Thank you. — kefomo
– kefomo, Commented Dec 28, 2022 at 20:25
I was trying escapeReplacement but that didn't work. Glad I found your comment... — steven smith
– steven smith, Commented May 19, 2023 at 22:07

Mahozad · Accepted Answer · 2025-09-08 18:37:12Z

1

Use Regex.fromLiteral() function:

val regex = Regex.fromLiteral("? a [+")
println("? a [+" matches regex) // true

As said by @Slaw in comments, you can also use Regex.escape() function:

val escaped = Regex.escape("? a [+")
println("? a [+" matches Regex(escaped)) // true

answered Sep 8 at 18:37

Mahozad

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3 Comments

Barmar Sep 8 at 19:19

The documentation of the two functions is identical. Do you know why both exist?

Mahozad Sep 8 at 19:22

fromLiteral returns a Regex but escape returns a String.

Barmar Sep 8 at 19:24

So escape is likely to be more useful if you need to combine it with some other string before converting the result to a Regex. Which is the common reason for needing this functionality in the first place.

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