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 >
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.

By: reklis
2010-07-01 05:48:02

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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 :-)
flatcap · 412 weeks and 2 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)
quincymd · 412 weeks and 2 days ago

What do you think?

Any thoughts on this command? Does it work on your machine? Can you do the same thing with only 14 characters?

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