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Sed Command, How to copy a string usin sed

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eveaug	Posted: May 6 2005, 04:52 PM
Newbie Group: Members Posts: 1 Member No.: 977 Joined: 6-May 05	Hi Using sed is it possible to copy a string from a line in a file to another location on the same line: Example file: aaa bbb ccc eee fff ggg to become aaa bbb ccc > ccc eee fff ggg > ggg ? Any help would be great Thanks

andyb1ack

Posted: May 10 2005, 04:01 PM

User Level: 4

Group: Members
Posts: 98
Member No.: 513
Joined: 9-September 04

Uh-oh. This isn't going to be easy to explain, but here's the code for your example:

CODE

$ cat /var/tmp/asb
aaa bbb ccc
eee fff ggg

$ sed 's/$.*$ $.*$/\1 \2 > \2/' /var/tmp/asb
aaa bbb ccc > ccc
eee fff ggg > ggg

I've split up each line into two parts separated by a space.
. = any character
* = 0 or more of the preceeding character
hence .* = 0 or more of any character

$.*$ means save anything into named space 1

Repeat it with a space in between
ie the $.*$ $.*$
means, put everything up to the last space into named space 1, and from the last space to the end of the line in named space 2.

I could have done it the following way too:

CODE

$ sed 's/$.*$ $.*$ $.*$/\1 \2 \3 > \3/' /var/tmp/asb
aaa bbb ccc > ccc
eee fff ggg > ggg

Alternately, you could have used the following shell commands:

CODE

cat /var/tmp/asb |while read A B C
do
echo $A $B $C \> $C
done

vibhor_agarwalin	Posted: May 11 2005, 02:47 PM
User Level: 3 Group: Members Posts: 34 Member No.: 788 Joined: 1-February 05	Hi Andy, I remember you and your sed explanation. I am able to solve most of my problems with the sed, but i am a bit new to your while and read one. Can you help me a bit in that.

andyb1ack

Posted: May 11 2005, 03:21 PM

User Level: 4

Group: Members
Posts: 98
Member No.: 513
Joined: 9-September 04

The while read contruct is really useful.
You can put configuration info into a file and have it read by a script.
To change the script you just then update the config file, which is better practice than updating code.

The important thing to ensure is that each line in the config file has the number of fields as you expect, or things start going a bit funny!

Here's an example of a simple while read in action:

CODE

$ cat /var/tmp/asb.dirs
/var/tmp/logs/big_accounts_job 4
/var/tmp/logs/small_accounts_job 10
/var/tmp/logs/backups 30

$ cat /var/tmp/asb.hk_dirs.sh
#/bin/ksh
cat /var/tmp/asb.dirs |while read DIR DAYS
do
echo find ${DIR} -mtime +${DAYS} -exec rm {} \;
done

$ ksh /var/tmp/asb.hk_dirs.sh
find /var/tmp/logs/big_accounts_job -mtime +4 -exec rm {};
find /var/tmp/logs/small_accounts_job -mtime +10 -exec rm {};
find /var/tmp/logs/backups -mtime +30 -exec rm {};

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