Jenkinsfile/Groovy: how to use variables in regex pattern find-counts? - regex

Question

In the following declarative syntax pipeline:
pipeline {
agent any
stages {
stage( "1" ) {
steps {
script {
orig = "/path/to/file"
two_lev_down = (orig =~ /^(?:\/[^\/]*){2}(.*)/)[0][1]
echo "${two_lev_down}"
depth = 2
two_lev_down = (orig =~ /^(?:\/[^\/]*){depth}(.*)/)[0][1]
echo "${two_lev_down}"
}
}
}
}
}
...the regex is meant to match everything after the third instance of "/".
The first, i.e. (orig =~ /^(?:\/[^\/]*){2}(.*)/)[0][1] works.
But the second, (orig =~ /^(?:\/[^\/]*){depth}(.*)/)[0][1] does not. It generates this error:
java.util.regex.PatternSyntaxException: Illegal repetition near index 10
^(?:/[^/]*){depth}(.*)
I assume the problem is the use of the variable depth instead of a hardcoded integer, since that's the only difference between the working code and error-generating code.
How can I use a Groovy variable in a regex pattern find-count? Or what is the Groovy-language idiomatic way to write a regex that returns everything after the nth occurrence of a pattern?

Answer 1

You are missing the $ in front of your variable. It should be:
orig = "/path/to/file"
depth = 2
two_lev_down = (orig =~ /^(?:\/[^\/]*){$depth}(.*)/)[0][1]
assert '/file' == two_lev_down
Why?
In Groovy the String-interpolation (over GString) works for 3 String literals:
usual double quotes: "Hello $world, my name is ${name.toUpperCase()}"
Slashy-strings used usually as regexp-literals: /.{$depth}/
Multi-line double-quoted Strings:
def email = """
Dear ${user}.
Thank your for blablah.
"""