How to convert Epoch Time stamp to basic date time

[its4...@gmail.com]

Hello 

Ho to convert Epoch time stamp to basic date time 

my config file looks like below 

<source>

  type tail

  path /var/log/snmptraps.log

  read_from_head true

  tag snmplog

  format multiline

  format_firstline /^\</

  format1 /(?<time>\d+)(?:,\W)(?<Severity>[^"]+)(?:",\d[\W]+")/

</source>

<match *.**>

  type copy

  <store>

    type elasticsearch

    host localhost

    port 9200

    flush_interval 10s

  </store>

</match>

here I 've to conver the 'time' field to basic date time format as it is coming as epoch in log I tried to change my config as below but its not working 

<source>

  type tail

  path /var/log/snmptraps.log

  read_from_head true

  tag snmplog

  format multiline

  format_firstline /^\</

  format1 /(?<time>\d+)(?:,\W)(?<Severity>[^"]+)(?:",\d[\W]+")/

  time_format ${Time.at(time_format).strftime('%Y-%m-%d %H:%M:%S')}

</source>

<match *.**>

  type copy

  <store>

    type elasticsearch

    host localhost

    port 9200

    logstash_format true

    flush_interval 10s

  </store>

</match>

any help plz?

thanks 

Arun