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grep multiple lines

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August 9th, 2007 mysurface Posted in Text Manipulation, grep | Hits: 53486 |

You can grep multiple lines before or after matching the keywords. Here is a simple tips, that what I discover grep capable of. A is after, B is before.

Let say you have the message.txt shows as below:


Aug  5 02:43:12 zion kernel: [    0.000000] Zone PFN ranges:
Aug  5 02:43:12 zion kernel: [    0.000000]   DMA             0 ->     4096
Aug  5 02:43:12 zion kernel: [    0.000000]   Normal       4096 ->   130730
Aug  5 02:43:12 zion kernel: [    0.000000]   HighMem    130730 ->   130730
Aug  5 02:43:12 zion kernel: [    0.000000] early_node_map[1] active PFN ranges
Aug  5 02:43:12 zion kernel: [    0.000000]     0:        0 ->   130730
Aug  5 02:43:12 zion kernel: [    0.000000] DMI 2.3 present.

You can grep “DMA” with -B 1 and -A2

grep -B1 -A2 "DMA" message.txt

It will return

Aug  5 02:43:12 zion kernel: [    0.000000] Zone PFN ranges:
Aug  5 02:43:12 zion kernel: [    0.000000]   DMA             0 ->     4096
Aug  5 02:43:12 zion kernel: [    0.000000]   Normal       4096 ->   130730
Aug  5 02:43:12 zion kernel: [    0.000000]   HighMem    130730 ->   130730

It is useful to grep logs with multiple lines for one entry.

[中文翻译]

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11 Responses to “grep multiple lines”

  1. Planet Malaysia Says:
    September 3rd, 2007 at 10:29 am

    This is damm cool. Never use this option before. Thanks for your tips.

  2. JD Says:
    September 11th, 2007 at 6:40 am

    I use that feature all the time. I think grep & sed are my best friends. :)

  3. michel Says:
    March 7th, 2008 at 11:27 pm

    Could you please me how to do the same in HP-UX?
    Thank you in advance

  4. Sasikanth Malladi Says:
    October 17th, 2008 at 11:42 pm

    To do the same on HP-UX, just install GNU grep on your machine.

  5. Shery Vijayan Says:
    August 11th, 2009 at 4:05 pm

    Thanks pal , for the tip.
    That was extremely usefull.
    –Shery

  6. Neeraj Says:
    November 20th, 2009 at 12:34 am

    I have a slightly more complicated problem. Let’s assume I have a file like below

    sdfsdghf
    DMA
    DMA
    45346768
    sdfsdgfh
    DMA
    DMA
    DMA
    5236472646
    DMA
    *&*(&*(&

    Now I want to find out how many times DMA appear in consecutive lines. How can I do that? In above case I should get result as 2, 3 & 1

  7. Andre Says:
    December 7th, 2009 at 7:46 pm

    Try using
    uniq -c | grep DMA

  8. Allan Says:
    February 24th, 2010 at 2:25 am

    That is an awesome tip. I was going to write an Perl script to extract stuff like this, but figure I should check Grep’s awesome utility first. Thanks!!

  9. Nox Says:
    April 1st, 2010 at 10:12 am

    grep -B1 -A2 “DMA” message.txt works very well, but what if I want to filter away all such matches?

    Normally the -v option will do, but it doesn’t seem to work with -B or -A options… Any clue?

  10. Divya Says:
    April 7th, 2010 at 9:41 pm

    What if the my pattern is not fixed but i want get a block of data?
    For example in a big file i have this whole string
    ##
    # Host alias specification
    ##
    Host_Alias SPARC = bigtime, eclipse, moet, anchor:\
    SGI = grolsch, dandelion, black:\
    ALPHA = widget, thalamus, foobar:\
    HPPA = boa, nag, python
    Host_Alias CUNETS = 128.138.0.0/255.255.0.0
    Host_Alias CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0
    Host_Alias SERVERS = master, mail, www, ns
    Host_Alias CDROM = orion, perseus, hercules

    ##

    Host_Alias SPARC = bigtime, eclipse, moet, anchor:\
    SGI = grolsch, dandelion, black:\
    ALPHA = widget, thalamus, foobar:\
    HPPA = boa, nag, python

    This is a single line comin

    I have smthng like this…
    how can get all lines starting with host alias?

  11. Steve Says:
    April 13th, 2010 at 4:52 am

    This is the file that I am reading. When I run grep looking for “Core0″ or “Core1″ I get two results back. How can I seperate the different returns? -b 1 will give me the last item but, I cannot find a way to get just the first item of the pair.

    8temp-pci-00c3
    Adapter: PCI adapter
    Core0 Temp: +44.0°C
    Core0 Temp: +41.0°C
    Core1 Temp: +37.0°C
    Core1 Temp: +41.0°C

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