I have a use case where given a rule like: RULE:[1:$1@$0](.*@FOO.COM)s/@.*// want *all* of the below username's to match user1@FOO.COM user2@foo.com user3@FOO.com I tried modifying the above rule to use the RegEx modifier that makes the (regexp) case insensitive: RULE:[1:$1@$0]((?i)(.*@FOO.COM))s/@.*// However on testing with this rule I get an error : $ hadoop org.apache.hadoop.security.HadoopKerberosName user1@FOO.COM Exception in thread "main" java.util.regex.PatternSyntaxException: Unknown inline modifier near index 3 (?i ^ at java.util.regex.Pattern.error(Pattern.java:1957) at java.util.regex.Pattern.group0(Pattern.java:2896) at java.util.regex.Pattern.sequence(Pattern.java:2053) at java.util.regex.Pattern.expr(Pattern.java:1998) at java.util.regex.Pattern.compile(Pattern.java:1698) at java.util.regex.Pattern.<init>(Pattern.java:1351) at java.util.regex.Pattern.compile(Pattern.java:1028) at org.apache.hadoop.security.authentication.util.KerberosName$Rule.<init>(KerberosName.java:193) at org.apache.hadoop.security.authentication.util.KerberosName.parseRules(KerberosName.java:342) at org.apache.hadoop.security.authentication.util.KerberosName.setRules(KerberosName.java:398) at org.apache.hadoop.security.HadoopKerberosName.setConfiguration(HadoopKerberosName.java:75) at org.apache.hadoop.security.HadoopKerberosName.main(HadoopKerberosName.java:79) Any idea what I'm doing wrong ? ... View more