Scala: concatenating a string in a regex pattern string causing issue

Question

If I am doing this it is working fine:

val string = "somestring;userid=someidT;otherstuffs"

var pattern = """[;?&]userid=([^;&]+)?(;|&|$)""".r

val result = pattern.findFirstMatchIn(string).get;

But I am getting an error when I am doing this

val string = "somestring;userid=someidT;otherstuffs"

val id_name = "userid"

var pattern = """[;?&]""" + id_name + """=([^;&]+)?(;|&|$)""".r

val result = pattern.findFirstMatchIn(string).get;

This is the error:

error: value findFirstMatchIn is not a member of String

Wiktor Stribiżew · Accepted Answer · 2017-07-17 21:17:21Z

3

You may use an interpolated string literal and use a bit simpler regex:

val string = "somestring;userid=someidT;otherstuffs"
val id_name = "userid"
var pattern = s"[;?&]${id_name}=([^;&]*)".r
val result = pattern.findFirstMatchIn(string).get.group(1)
println(result)
// => someidT

See the Scala demo.

The [;?&]$id_name=([^;&]*) pattern finds ;, ? or & and then userId (since ${id_name} is interpolated) and then = is matched and then any 0+ chars other than ; and & are captured into Group 1 that is returned.

NOTE: if you want to use a $ as an end of string anchor in the interpolated string literal use $$.

Also, remember to Regex.quote("pattern") if the variable may contain special regex operators like (, ), [, etc. See Scala: regex, escape string.

edited Jul 17, 2017 at 21:17

answered Jul 17, 2017 at 21:00

Wiktor Stribiżew

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3 Comments

user557597 Over a year ago

I believe he requires ([;&]|$) at the end as well.

Wiktor Stribiżew Over a year ago

Then it should be ([;&]|$$) in the interpolated string literal. I believe it does not matter here.

user557597 Over a year ago

That looks required to me, how doesn't it matter?

akuiper · Accepted Answer · 2017-07-17 20:27:31Z

2

Add parenthesis around the string so that regex is made after the string has been constructed instead of the other way around:

var pattern = ("[;?&]" + id_name + "=([^;&]+)?(;|&|$)").r
// pattern: scala.util.matching.Regex = [;?&]userid=([^;&]+)?(;|&|$)

val result = pattern.findFirstMatchIn(string).get;
// result: scala.util.matching.Regex.Match = ;userid=someidT;

answered Jul 17, 2017 at 20:27

akuiper

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