How do I grep multiple lines (output from another command) at the same time?

Question

I have a Linux driver running in the background that is able to return the current system data/stats. I view the data by running a console utility (let's call it dump-data) in a console. All data is dumped every time I run dump-data. The output of the utility is like below

Output:
- A=reading1
- B=reading2
- C=reading3
- D=reading4
- E=reading5
...
- variableX=readingX
...

The list of readings returned by the utility can be really long. Depending on the scenario, certain readings would be useful while everything else would be useless.

I need a way to grep only the useful readings whose names might have have nothing in common (via a bash script). I.e. Sometimes I'll need to collect A,D,E; and other times I'll need C,D,E.

I'm attempting to graph the readings over time to look for trends, so I can't run something like this:

# forgive my pseudocode
Loop
    dump-data | grep A
    dump-data | grep D
    dump-data | grep E
End Loop

to collect A,D,E as that would actually give me readings from 3 separate calls of dump-data as that would not be accurate.

Igor Chubin · Accepted Answer · 2012-08-02 08:56:27Z

5

If you want to save all result of grep in the same file, you can just join all expressions in one:

grep -E 'expr1|expr2|expr3'

But if you want to have results (for expr1, expr2 and expr3) in separate files, things are getting more interesting.

You can do this using tee >(command).

For example, here I process the same pipe with thre different commands:

$ echo abc | tee >(sed s/a/_a_/ > file1) | tee >(sed s/b/_b_/ > file2) | sed s/c/_c_/ > file3
$ grep "" file[123]
file1:_a_bc
file2:a_b_c
file3:ab_c_

But the command seems to be too complex.

I would better save dump-data results to a file and then grep it.

TEMP=$(mktemp /tmp/dump-data-XXXXXXXX)
dump-data > ${TEMP}
grep A ${TEMP}
grep B ${TEMP}
grep C ${TEMP}

edited Aug 2, 2012 at 8:56

answered Aug 2, 2012 at 8:45

Igor Chubin

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2 Comments

peonicles Over a year ago

Thanks for your answer! grep -E worked fine. I selected your answer as it offered a little more than the rest. I did think of your last solution, but as I might take readings pretty often it might be a little inefficient.

Igor Chubin Over a year ago

yes of course, but when you need separate output files for each expression, it is inevitable :) when not, of course, not :)

scai · Accepted Answer · 2012-08-02 08:45:24Z

3

You can use dump-data | grep -E "A|D|E". Note the -E option of grep. Alternatively you could use egrep without the -E option.

answered Aug 2, 2012 at 8:45

scai

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Comments

Vijay · Accepted Answer · 2012-08-02 08:45:32Z

2

you can simply use:

dump-data | grep -E 'A|D|E'

answered Aug 2, 2012 at 8:45

Vijay

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Community · Accepted Answer · 2017-04-13 12:36:24Z

0

awk '/MY PATTERN/{print > "matches-"FILENAME;}' myfile{1,3}

thx Guru at Stack Exchange

edited Apr 13, 2017 at 12:36

CommunityBot

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answered Nov 16, 2014 at 17:29

Antonio Junior

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