CODEWITHSUNDEEP
bashawkgreptail
onur
onur

Reputation: 6395

How to start from the last line with tail?

I have a huge log file. I need to find something and print last line. Like this:

tail -n +1 "$log" | awk '$9 ~ "'$something'" {print $0}' | tail -n1

But when I execute this command, tail starts from 1st line and reads all the lines. And running few mins.

How can I start to read from the last line and stop when I find something? So maybe I don't need to read all lines and running just few secs. Because I need just last line about $something.

Upvotes: 2

Views: 5979

Answers (4)

fedorqui
fedorqui

Reputation: 290515

Note you are saying tail -n +1 "$log", which is interpreted by tail as: start reading from line 1. So you are in fact doing cat "$log".

You probably want to say tail -n 1 "$log" (without the + before 1) to get the last n lines.

Also, if you want to get the last match of $something, you may want to use tac. This prints a file backwards: first the last line, then the penultimate... and finally the first one.

So if you do

tac "$log" | grep -m1 "$something"

this will print the last match of $something and then exit, because -mX prints the first X matches.

Or of course you can use awk as well:

tac "$log" | awk -v pattern="$something" '$9 ~ pattern {print; exit}'

Note the usage of -v to give to awk the variable. This way you avoid a confusing mixure of single and double quotes in your code.

Upvotes: 4

fredtantini
fredtantini

Reputation: 16586

Instead of tail, use tac. It will reverse the file and you can exit when you first grep something:

tac "$log" | awk '$9 ~ "'$something'" {print $0;exit}'

Upvotes: 2

Reut Sharabani
Reut Sharabani

Reputation: 31349

tac $FILE | grep $SOMETHING -m 1

tac: the reverse of cat :-)

grep -m: search and stop on first occurrence

Upvotes: 2

geert3
geert3

Reputation: 7351

tail -1000 takes only the last 1000 lines from your file. You could grep that part, but you wouldn't know if the thing you grep for occurred in the earlier lines. There's no way to grep "backwards".

Upvotes: 1

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