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Script to replace string in a file-Urgent pls

Hi,

Can someone help me with a script to replace a particular string in a file?

Thanks and Regards,

karthik

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jlevie

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yuzh

Let's say you want to relpace "name" with "MyName" in a file myfile:

cat myfile | sed 's/name/MyName/g' > myfile

jlevie

yzuh,

Your method will work with small files, but you can get into trouble if the file is of significant size. What happens then is that sed starts writing to the file as you read it and maddness can result (you can probably figure out how I found that out).

yuzh

You are correct jlevie,

it should be something like:
sed 's/name/MyName/g' myfile > myfile.tmp
mv myfile.tmp myfile

ahoffmann

jlevie, yuzh,
I use the
(cat file)| prog > file
method since years, mainly on SunOS and Solaris (never failed for me), but I know that on Linux the limit is around 8k, while some other UNIX (IRIX, AIX) may fail at all.
I'm aware that the problem is somehwere in the combination of CPU&OS&shell, but never got completely used to it.
Does anybody have more information or docs about it?

jlevie

Yeah, I'd used the simple form for years on Solaris (and SunOS) until I got bit by it one day with a many-multi-meg file. I suspect that it may not be a simple limit on Solaris, but may be influenced by the system resources. And yes Linux does have a much lower limit.

Since then I've made it a practice to always move the input file to a different name and write the output to the original file name.

ahoffmann

haha, that's why I like it on SunOS for multi-mega-meg files and no space left on device and no perl ;-)
but the draegon always hits me on other systems ...
(practice is the save way now: mv or perl, 'cause of huge disks, but the ancient systems are still running)

yuzh

Sometime a sigle file could be a few GB, it will fail, if you don't use tmp file. The Engerring simulation log file could be huge,the same thing with some of the C-ISAM index file)

ahoffmann

yuzh,
as I said: I'm aware that it fails on most systems, but I'm doing it since the time of dawn on SunOS (3.x) SPARC for multi-100meg files, and it never failed.
Once, in a long night, I debugged the bahaviour, and it seems that on SPARC CPUs the reason might be the special register mapping (input vs. output register window) when switching between functions, 'couse the seek pointer is in a register and seems to be a physical (disk?) address.

I'm just curious how it works in detail, sometimes, somewhere

karthik_selamel

ASKER

Hi all,

Well.The following worked fo r me and served the purpose.

Within the vi Editor

at the exit prompt ie., :%s/source-string/Desti-string/g

did waht I wanted.

Regards,

Karthik

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