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reversing order of lines in a file

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# 1  
Old 03-02-2007
Error reversing order of lines in a file
how can i reverse the line order in text files?
(but total number of the lines is not constant )

for example i have a file like this:

line1
line2
line3
.
.
lineN


i wantto make it like this:

lineN
.
.
.
line3
line2
line1
# 2  
Old 03-02-2007
U can try something like this>

#!/usr/bin/awk -f

#< AWK - Reverse order of words in each line of a file

{ cnt = NF;
while ( cnt > 0 ) {
printf( "%s ", $cnt );
--cnt;
}
printf( "\n" );
}
# 3  
Old 03-02-2007
Quote:
Originally Posted by gfhgfnhhn
how can i reverse the line order in text files?
(but total number of the lines is not constant )

for example i have a file like this:

line1
line2
line3
.
.
lineN


i wantto make it like this:

lineN
.
.
.
line3
line2
line1
There is a GNU utility called tac, part of coreutils, that does what you want.

If you don't have it, and cannot install it:

Code:
awk '{x[NR] = $0}
 END { while ( NR > 0 ) print x[NR--] }' [FILENAME ...]

# 4  
Old 03-02-2007
Code:
sed '1!G;h;$!d'    file
sed -n '1!G;h;$p' file


from sed - one liners
# 5  
Old 03-02-2007
Try this...

Code:
cat -n <filename>| sort -r | cut -f2-20 > reversedfile

Experts please comment if anything wrong with this.... Smilie
# 6  
Old 03-02-2007
Reversal using tail & heads
Though complex , You can have script presented below does the job!!

#!/bin/ksh
Tot=$(sed -n $= FILE )
i=0;
while [[ $i -le $Tot ]] ; do
tail -n"$i" FILE | head -1
((i=i+1))
done

You can extend the script for multiple files. Experts please comment on the approach
# 7  
Old 03-02-2007
Quote:
Originally Posted by ennstate
Though complex , You can have script presented below does the job!!

#!/bin/ksh
Tot=$(sed -n $= FILE )
i=0;
while [[ $i -le $Tot ]] ; do
tail -n"$i" FILE | head -1
((i=i+1))
done

You can extend the script for multiple files. Experts please comment on the approach
This is horrendously slow, as it calls two external commands for every line in the file. Here are timings for a 181-line file (xx.sh is your script):

Code:
 $ time tac .bashrc > /dev/null

real    0m0.021s
user    0m0.002s
sys     0m0.005s
$ time awk '{x[NR]=$0}END{while (NR) print x[NR--]}' .bashrc > /dev/null

real    0m0.010s
user    0m0.003s
sys     0m0.006s
$ time xx.sh .bashrc > /dev/null

real    0m2.060s
user    0m0.483s
sys     0m1.420s
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