bash: lines of a file in reverse order?

[Scott Elcomb]

On 8/24/06, Gregory D Hough <mr6re9-mI4xJ4qlgtBiLUuM0BA3LQ at public.gmane.org> wrote:
> >    Use tac:
> >
> > tac filename
> >
> >> I want to find the "last matching line" in a large log file.  My hope
> >> was:
> >>
> >> tail -50 -r filename | grep -m 1 "matching"
> >> would grab it for me if it exists in the last 50 lines of the log.
> >
> >
> > grep "PATTERN" filename | tail -n1
> >
> A
> #!/bin/bash
> grep "INVALID" /var/log/messages | tail -n1
>
>   time sh A
> Aug 24 15:52:22 localhost kernel: INVALID: IN=eth1 OUT= SRC=69.63.65.165
>
> real    0m0.044s
> user    0m0.001s
> sys     0m0.015s
>
>
> B
> #!/bin/bash
> tail -50 /var/log/messages | tac | grep -m1 "INVALID"
>
>   time sh B
> Aug 24 15:52:22 localhost kernel: INVALID: IN=eth1 OUT= SRC=69.63.65.165
>
> real    0m0.048s
> user    0m0.004s
> sys     0m0.016s
>
> Yep, method A is 4 to 5 thou faster than B most of the time

That's kinda cool.  Might get more accuracy on the last statment if
others' results were averaged in.

Still, that's a really interesting test, thanks for the results.  Is
there a way to track memory usage during the same periods?

-- 
Scott Elcomb
http://atomos.sourceforge.net/
http://search.cpan.org/~selcomb/SAL-3.03/
http://psema4.googlepages.com/

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