Shell Programming and Scripting

in my file, i like to search for a string and if there is a match then i want to replace it with someother string(like in windows wordpad).
i only know how to search for a pattern....[ if( /pattern/ ) ] but i dont know how to replace it..

and
1). i think it is there in unix grep or some other commends... if so.. what is that..
2.) how to do that in perl..
3.)what is good idea... doing that work(finding and replacing a str) in unix shell scripting or perl scripting..

Code:

sed -i -e 's/pattern/replacement/global-flag" input.txt

you can open the file in vi and use %s/"old string"/"new string"/g in the command mode.

with perl...
eg:

$ cat test
abc def xyz 123 456 789
$ perl -pi -e 's|abc|123|g' test
$ cat test
123 def xyz 123 456 789

to backup the original file use -pi.bak option & your original file will be saved as .bak

---------------------------------------------
$ sed -i -e 's/sekar/SEKAR/g' test.log
sed: illegal option -- i
Usage: sed [-n] [-e script] [-f source_file] [file...]
---------------------------------------------

i am with hp unix B.11.11 U 9000/800

In that case, redirect the output to another file and then rename it.

The -i option is only available with GNU sed.

If you have perl installed at your site inplace substitution is easy - take a look at ashterix's post above.

Cheers
ZB