topic Re: replacing according to position in Operating System - Linux

replacing according to position

Reen — Mon, 09 Apr 2007 05:21:42 GMT

Hi all,
can anybody help in this
In a line, i have a pattern tat is to be replaced.

using sed , i can replace in a particular line, but tat pattern can occur in the line in many other places.
i want only one instance to be replaced.

Re: replacing according to position

Reen — Mon, 09 Apr 2007 05:26:17 GMT

Attached is the file.
I want the 2nd instance of Blore to b replaced in 2nd line.
But in the actual file am not sure of the occurance of this instance.It can be 3rd instance.
But the position is fixed.
so in this case, 23-27 characters in 2nd line to be replaced by Mlore

Re: replacing according to position

Dennis Handly — Mon, 09 Apr 2007 05:28:00 GMT

>using sed, i can replace in a particular line, but that pattern can occur in the line in many other places. i want only one instance to be replaced.

One instance per line, or one per whole file?
For the former, don't add "g" to the "s" function, then it only will replace one.

If it is once per file, you'll need to write an awk script. To replace to the first then copy the rest of the file.

Re: replacing according to position

Reen — Mon, 09 Apr 2007 05:48:34 GMT

Thanks Dennis.
Can u give me a solution for my attached file

Re: replacing according to position

Yogeeraj_1 — Mon, 09 Apr 2007 06:18:30 GMT

hi Reen@,

In the vi editor, can you try this:
:1,$s/.Blore/Mlore

kind regards
yogeeraj

Re: replacing according to position

Dennis Handly — Mon, 09 Apr 2007 06:33:56 GMT

>Yogeeraj: 1,$s/.Blore/Mlore

You may need to quote the "." otherwise it would match the first:
:1,$s/\.Blore/Mlore

(But I guess it was safe since there are no chars before the first Blore.)

>But the position is fixed. so in this case, 23-27 characters in 2nd line to be replaced by Mlore

That makes it easy:
sed -e 's/^$......................$Blore/\1Mlore/'

(There should be 22 dots. The \1 puts them back into the output. If only one the second line, you can use '2s/'.)

Re: replacing according to position

James R. Ferguson — Mon, 09 Apr 2007 06:50:39 GMT

Hi:

A bit more readable (and much easier to maintain) is the specificatino of the number of character repetitions, thusly:

# sed -e 's/^$.\{22\}$Blore/\1Mlore/'

Note that the curly braces must be escaped with a backslash just like the parentheses must be.

Regards!

...JRF...

Re: replacing according to position

Reen — Mon, 09 Apr 2007 23:49:29 GMT

Hi all,
Thanks a lot for the help.
One more query is that,
is ther any restriction on the no. of characters?
I mean.. in a line can i change the 260-264th character in the similar manner?
I hav to achieve that.

Re: replacing according to position

Dennis Handly — Mon, 09 Apr 2007 23:57:06 GMT

>is there any restriction on the no. of characters?

No, you can use JRF's improvement, and you just type in the number.
^$.\{259\}$

Re: replacing according to position

Reen — Tue, 10 Apr 2007 00:04:55 GMT

Dennis,
Didnt get JRF`s improvement???

Re: replacing according to position

Reen — Tue, 10 Apr 2007 00:09:58 GMT

Ok
But When i type in 272nd character sed function cannot be parsed error occurs.
Till 255th character,its fine.
Cant replace 256th character onwards in a line. Any suggestions?

Re: replacing according to position

Dennis Handly — Tue, 10 Apr 2007 00:13:25 GMT

>Didnt get JRF`s improvement???

Instead of typing 22 "."s, you can use: .\{22\}

If you are happy with your answers, please read:
http://forums1.itrc.hp.com/service/forums/helptips.do?#33

Re: replacing according to position

Reen — Tue, 10 Apr 2007 00:23:39 GMT

But Dennis,
I cant replace 272-275th character..

Re: replacing according to position

Dennis Handly — Tue, 10 Apr 2007 00:59:46 GMT

>But when i type in 272nd character sed function cannot be parsed error occurs. Till 255th character, it's fine.

Ah, that limit is documented under regexp(5).

You are going to have to do addition:
$ sed -e 's/^$.\{200\}.\{71\}$Blore/\1Mlore/'

Re: replacing according to position

Reen — Tue, 10 Apr 2007 04:25:01 GMT

Hey... tats cool

thanks a lot...
got the solution!