mjhjmtu

I am looking for a command where I can grep 20 or more lines after a specific match.

Example: grep "09:55:21,651" mylog_file.log

2018-02-26 09:55:21,651 ERROR [WebContainer : 0] (CommonAction.java:253) - SITAConnector Error: Empty SITA Response XML
com.ac.ccaswitch.exception.SitaConnectorException: Empty SITA Response XML
 at com.ac.ccaswitch.connector.sita.SITAConnector.sendToSitaQueue(SITAConnector.java:144)
 at com.ac.ccaswitch.entry.CommonAction.performTask(CommonAction.java:212)
 at com.ac.ccaswitch.entry.PaymentServlet.doPost(PaymentServlet.java:85)
 at javax.servlet.http.HttpServlet.service(HttpServlet.java:738)
 at javax.servlet.http.HttpServlet.service(HttpServlet.java:831)
 at com.ibm.ws.webcontainer.servlet.ServletWrapper.service(ServletWrapper.java:1694)
 at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:970)
 at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:508)
 at com.ibm.ws.webcontainer.servlet.ServletWrapperImpl.handleRequest(ServletWrapperImpl.java:181)
 at com.ibm.ws.webcontainer.servlet.CacheServletWrapper.handleRequest(CacheServletWrapper.java:91)
 at com.ibm.ws.webcontainer.WebContainer.handleRequest(WebContainer.java:878)
 at com.ibm.ws.webcontainer.WSWebContainer.handleRequest(WSWebContainer.java:1592)
 at com.ibm.ws.webcontainer.channel.WCChannelLink.ready(WCChannelLink.java:191)
 at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleDiscrimination(HttpInboundLink.java:454)
 at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleNewRequest(HttpInboundLink.java:516)
 at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.processRequest(HttpInboundLink.java:307)
 at com.ibm.ws.http.channel.inbound.impl.HttpICLReadCallback.complete(HttpICLReadCallback.java:84)
 at com.ibm.ws.tcp.channel.impl.AioReadCompletionListener.futureCompleted(AioReadCompletionListener.java:175)
 at com.ibm.io.async.AbstractAsyncFuture.invokeCallback(AbstractAsyncFuture.java:217)
 at com.ibm.io.async.AsyncChannelFuture.fireCompletionActions(AsyncChannelFuture.java:161)
 at com.ibm.io.async.AsyncFuture.completed(AsyncFuture.java:138)
 at com.ibm.io.async.ResultHandler.complete(ResultHandler.java:204)
 at com.ibm.io.async.ResultHandler.runEventProcessingLoop(ResultHandler.java:775)

you can use grep's -An switch to get n lines after the match so for your example that would be

grep -A20 "09:55:21,651" mylog_file.log

EDIT:
It looks like your version of grep does not support -A.
So here is a small script you can use instead

#!/bin/sh
file="$1"
pattern="$2"
n="$3"
matches="$(grep -n $pattern $file)"
echo "$matches" | while read match; do
 line="$match%%:*"
 sed -n "$line,$(($line + $n - 1))p" < "$file"
done

you can use it like this: sh script.sh mylog_file.log "09:55:21,651" 20

EDIT2: While I am at it here is a solution that uses head and tail instead of sed just in case your sed is weird aswell

#!/bin/sh
file="$1"
pattern="$2"
n="$3"
matches="$(grep -n $pattern $file)"
echo "$matches" | while read match; do
 line="$match%%:*"
 head "-$(($line + $n - 1))" "$file" | tail "-$n"
done