How to get first char of a message in logstash filter

Question

I would like to get the firs char of the message in order to apply either xml or json filter but I don't even know how to start ```

filter {
  if [type]=="mom_rubens" {
    if [message] = "<*" {
      xml {
        source => "message"
        store_xml => false
        xpath => [
          "/APIOS_MOM_EVENT/IDENT/NO_EMIARTE/text()", "NO_EMIARTE",
          "/APISTAT_EVENT/IDENT/NO_EMIARTE/text()", "NO_EMIARTE",
          "/APIOS_MOM_EVENT/DATA/APIOS_EXPORT/METADATA/VECTORS/VECTOR","VECTORS",
          "/APIOS_MOM_EVENT/DATA/APIOS_EXPORT/METADATA/VECTORS/VECTOR/@NAME","VECTOR_NAME",
          "/APIOS_MOM_EVENT/INFO_EVENT/SENDER/text()","SENDER",
          "/APISTAT_EVENT/INFO_EVENT/SENDER/text()","SENDER",
          "/APIOS_MOM_EVENT/DATA/APIOS_EXPORT/METADATA/VECTORS/VECTOR/@ONLINE","ON_LINE",
          "/APIOS_MOM_EVENT/DATA/APIOS_EXPORT/METADATA/VECTORS/VECTOR/@OFFLINE","OFF_LINE"
        ]
        target => "xml"
      }
    }
    else if [message] = "{*" {
      json {
        source => "message"
      }
    }
  }

```

if [message] = "

```

Thanks for your help

Best regards, Guillaume

Answer 1

Should be:

if [message] =~ /^<xml/ {
    ...
}