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Read multiple lines of a file based on regex matching a single line

Terminal - Read multiple lines of a file based on regex matching a single line
for i in `grep -n "SomeRegEx" foo.txt | sed 's/:/ /' | awk '{print $1}'`; do echo "head -n `echo "$i+4" | bc` foo.txt | tail -n 5"; done > headsandtails.sh
2010-07-01 05:48:02
User: reklis
Functions: awk echo sed
-2
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Read multiple lines of a file based on regex matching a single line

Finds the line number matching the regex, then passes that to BC for some math, passes that to head, and uses tail to trim off the unwanted section at the top. The whole thing is spit out to a script that can then be shared or run. Comes in handy for reading select sections from error logs.

Add to favourites | Report as malicious

Alternatives

There are 2 alternatives - vote for the best!

Terminal - Alternatives

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What others think

My god that's complicated. First of all, we don't need the awk bit, this will do:

| sed 's/:.*// |

If you're using bash, you can get rid of echo and bc, too:

$((i+4))

Also, head and tail are a bit inefficient, so let's use sed again:

sed -n $i,$((i+4))p

or

sed -n $i,+4p

But sed can do regexes too, so now we can replace the whole command with:

sed -n '/SomeRegEx/,+4p' foo.txt

No need for a script :-)

Comment by flatcap 154 weeks and 5 days ago

Or egrep:

egrep "SomeRegEx" -A 4 foo.txt

Options:

-A print lines after match

-B print lines after match

-C print lines before and after match (e.g 4 before and 4 after)

Comment by quincymd 154 weeks and 5 days ago

Your point of view

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