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theTuxRacer
Asked: 2011-02-24 22:02:54 +0800 CST

How to grep 2 or 3 lines, one containing the text I want, and the others just below it?

  • 772

This is a snapshot of error log:

06:16:29,933 ERROR EmailRMManager$:45 - Exception In get Message
com.rabbitmq.client.AlreadyClosedException: clean connection shutdown; reason: Attempt to use closed channel
    at com.rabbitmq.client.impl.AMQChannel.ensureIsOpen(AMQChannel.java:195)
    at com.rabbitmq.client.impl.AMQChannel.rpc(AMQChannel.java:222)
    at com.rabbitmq.client.impl.AMQChannel.rpc(AMQChannel.java:208)
    at com.rabbitmq.client.impl.AMQChannel.exnWrappingRpc(AMQChannel.java:139)
    at com.rabbitmq.client.impl.ChannelN.basicGet(ChannelN.java:645)

I do the following command:

cat foo.log | grep ERROR to get an OP as:

06:16:29,933 ERROR EmailRMManager$:45 - Exception In get Message

What command should I execute to get the output as 

06:16:29,933 ERROR EmailRMManager$:45 - Exception In get Message
    com.rabbitmq.client.AlreadyClosedException: clean connection shutdown; reason: Attempt to use closed channel

ie, also grep the line(s) after the pattern?

bash

4 Answers

  1. Best Answer

    Just do a:

    grep -A1 ERROR

    The -A1 tells grep to include 1 line after the match. -B includes lines before the match, in case you need that too.

    • 80

  2. For a more portable way, there's awk

    awk '/ERROR/{n=NR+1} n>=NR' foo.log

    Or maybe you want all the indented lines following?

    awk '/^[^[:blank:]]/{p=0} /ERROR/{p=1} p' foo.log
    • 5

  3. I have found this solution:

    cat apache.error.log | grep -Pzo '^.*?Exception In get Message.*?\ncom\.rabbitmq.*?(\n(?=\s).*?)*$'

    Where (\n(?=\s).*?)* means:

    • \n find next line
    • (?=\s) where is starts from whitespace character
    • .*? until end of line
    • (...)* Find such lines multiple times

    PS. You may turf this pattern \ncom\.rabbitmq.*? if second line begins from whitespace \s

    • 1

  4. For this simple task a simple way is:

    grep -A num
Print num lines of trailing context after each match. See also the -B and -C options.

grep -B num
Print num lines of leading context before each match. See also the -A and -C options.

grep -C num
Print num lines of leading and trailing context surrounding each match.
The default is 2 and is equivalent to -A 2 -B 2.

    Note: no whitespace may be given between the option and its argument.

    • 1