Need to read a file in reverse

Shell Programming and Scripting
1

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..

2

reading a file in reverse,

# !/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
3

thanks man!!

4

Just for info: If you have GNU coreutils installed, you'll find the tac utility (reversed cat :rolleyes: ) does the job of reading a file from bottom to top. But this won't find your match and break out for you :wink:

Cheers
ZB

1 Like
5

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

# reverse order of lines (emulates "tac")
 sed '1!G;h;$!d'               # method 1
 sed -n '1!G;h;$p'             # method 2
6

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