Question

This is my input file ..

 [root@localhost scripts]# cat ip6hdr.txt | xargs -n4
 6000 0000 005C 3320
 2001 0000 0000 0000
 0000 0000 0000 0100
 2001 0000 0000 0000
 0000 0000 0000 0200

I want to change the last two digits of first line of the file i.e. 20 to 00.

I tried this..

cat ip6hdr.txt | xargs -n4 | sed '1,1s/\([0-9]*\) \([0-9]*\) \([0-9]*\) \([0-9][0-9]\)\([0-9][0-9]\).*/\1 \2 \3 \400 /' 

Previously it was working fine on ubuntu now not working on fedora in a bash script

I have no reason why it works on one system and not on other one ..

 [root@localhost scripts]# sed --version
 GNU sed version 4.1.5
 Copyright (C) 2003 Free Software Foundation, Inc.
 This is free software; see the source for copying conditions.  There is NO
 warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE,
 to the extent permitted by law.

if possible suggest me some alternative ..

Answer 1

Why complicate things?

$ cat File
6000 0000 005C 3320
6000 0000 005C 3320

$ sed '1s/..$/00/;' File
6000 0000 005C 3300
6000 0000 005C 3320