[Gllug] Excluding matches with grep

[Wulf Forrester-Barker]

Andrew <ah at gnd.com> suggested:

grep SuSE-FW /var/log/gateway.messages | grep -v martian | grep -v
SPT=53 >ft.txt 

Alternatively, you could shorten that using egrep, which allows you to
specify several matches at the same time:

grep SuSE-FW /var/log/gateway.messages | egrep -v 'martian|SPT=53' >
ft.txt 

The pipe acts as the delimiter. One thing that might be worth doing,
unless the log files are relatively trivial in size, is figuring out
which filter has the most effect. For example, say you start off with
100MB of logfiles. If the grep command returns 50MB of data and the
egrep command only returns 10MB of data (assuming that most lines *do*
have martian, SPT=53 or any other identifier you want to use in), I'd
run the egrep one first. That way the second command is working on a
much smaller dataset and thus the whole process will run a lot quicker.

I use a variety of command line tools to gather data for monthy reports
on our intranet and I discovered that the 20+ minutes required by my awk
script (that does the bulk of the work) could be reduced to about 4
minutes by using grep to filter out all the lines that the awk script
ignores.

Wulf


-- 
Wulf Forrester-Barker (Webmaster)
The Lewisham Hospital NHS Trust
http://www.lewisham.nhs.uk/


wulf.f-b at uhl.nhs.uk

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