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Imagine the following file structure:

foo.bar.1 blabla moreblabla relevant=yes foo.bar.2 relevant=no foo.bar.3 blablabla foo.bar.4 relevant=yes

I want to retrieve all foo.bar lines where within the block following themselves and before the next foo.bar there is a line stating relevant=yes.

So the output should be:

foo.bar.1 foo.bar.4

I could of course write a program/script iterating through the lines, remembering the foo.bars and print them when there is a line saying relevant=yes following them an before the next foo.bar. But I thought there might be an out-of-the box way using standard Unix utilities (grep/sed/awk)?

Thanx for any hints!

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  • Chose awk solution as "answer" for being the clearest one in syntax. Commented Feb 3, 2016 at 20:07

3 Answers 3

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If the input is processed line by line, then processing needs to go like this:

  • if the current line is foo.bar, store it, forgetting any previous foo.bar line that wasn't enabled for output;
  • if the current line is relevant=yes, this enables the latest foo.bar for output.

This kind of reasoning is a job for awk. (It can also be done in sed if you like pain.)

awk ' /^foo\.bar/ { foobar = $0 } /^relevant=yes$/ {if (foobar != "") {print foobar; foobar = ""}} '
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  • Thanks for giving this awk solution. Pretty straight-forward. Commented Feb 2, 2016 at 19:55
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Here's one way with sed:

sed '/foo\.bar/h;/relevant=yes/!d;x;/foo\.bar/!d' infile

Lines matching foobar are copied to hold space. All lines, except those matching relevant=yes are deleted. Exchange hold space with pattern space (this only happens when lines match relevant=yes) and delete if it doesn't match foobar.

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  • I get an bash: !d': event not found, what am I doing wrong? Commented Feb 1, 2016 at 0:24
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    @userunknown - you're using bash... try with ! d that is, insert a space after each ! or try set +H before running the sed command Commented Feb 1, 2016 at 9:46
  • Thanks for giving this sed solution as well. Looks a little more painful than the awk-one imho as Gilles pointed out above. ;-) But I like it just as well. Commented Feb 3, 2016 at 18:54
  • @hal9000 - You're welcome ! I don't quite understand what's so painful about it but let's leave it at that. Commented Feb 3, 2016 at 19:00
  • @don_crissti - Sorry, sounded a little unfair. I admit it not being painful. It is just a very very little less straight-forward than awk imho. Was more catching the term Gilles used. Explanation: For someone not knowing sed perfectly well (count me in), the concept of spaces and exchanging them doesn't come clear just by looking at the syntax. The awk solution might be easier to grasp if you do not know either sed nor awk. But again, I loved to see a sed solution to this. This is why I pointed sed out as a tag. Commented Feb 3, 2016 at 20:17
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Pythonic way:

>>> with open("/home/xieerqi/textfile.txt") as file: ... for line in file: ... if line.__contains__("foo"): ... VAR = line ... if line.__contains__("relevant=yes"): ... print VAR ... foo.bar.1 foo.bar.4

Put together in a script:

DIR:/xieerqi skolodya@ubuntu:$ chmod +x relevance.py DIR:/xieerqi skolodya@ubuntu:$ ./relevance.py textfile.txt foo.bar.1 foo.bar.4 DIR:/xieerqi skolodya@ubuntu:$ cat relevance.py #!/usr/bin/env python import sys with open(sys.argv[1]) as file: for line in file: if line.__contains__("foo"): VAR = line.strip("\n") if line.__contains__("relevant=yes"): print VAR
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  • Thank you for the python solution though I prefer the other two solutions in this case. They are shorter and are what I meant when writing "out-of-the-box" in my initial question. But in the end your solution is just as fine. One thing though is taht when the pattern is a regular expression. awk and sed can handle them immediately whereas Python needs to be modified a little. (import re) Commented Feb 3, 2016 at 20:04
  • :) Fair comment - awk and sed are always better for text processing, and I do prefer them myself ( in fact awk is a big part of my reputation on the other site, askubuntu.com ), however both sed and awk solutions have been posted, so I thought I'd bright something else to the table. Hope in the end my answer was beneficial in some way to you and other users ! Commented Feb 3, 2016 at 20:20

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