Need to read a file in reverse - Shell Programming and Scripting

scorreg · #1 03-01-2006

I have to extract data from a text file which is huge in size >>10GB.
ie between two strings. If I do an ordinary sed it takes forever to come out. I was wondering if there was anyway to do the entire process in reverse and on finding the relevant string is there any way to break out of the search..

matrixmadhan · #2 03-01-2006

reading a file in reverse,

Code:

# !/usr/bin/ksh

linecnt=`wc -l file | awk '{print $1}'`

while [ $linecnt -ge 1 ]
do
sed -n "$linecnt"p file
linecnt=$(($linecnt - 1))
done

exit 0

scorreg · #3 03-01-2006

thanks man!!

zazzybob · #4 03-01-2006

Just for info: If you have GNU coreutils installed, you'll find the tac utility (reversed cat

) does the job of reading a file from bottom to top. But this won't find your match and break out for you

Cheers
ZB

Ygor · #5 03-01-2006

From "HANDY ONE-LINERS FOR SED" ...

Code:

# reverse order of lines (emulates "tac")
 sed '1!G;h;$!d'               # method 1
 sed -n '1!G;h;$p'             # method 2

vino · #6 03-01-2006

Similiar replies to a similiar post - sort a file in reverse order. I wonder how many use the search feature of the forum.

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