UNIX for Dummies Questions & Answers

Hello Can Any1 help me.

I want to replace a specific character string inside a file at a specific location with a particular character with the help of a command or a shell script.
The tr command replaces a specific character with another for all the occurences of that character in the file.
I don't know wat to do.

This replaces "test" with "old" in line 13

Code:

awk -v NEWSTRING="test" -v OLDSTRING="old" -v LINENUM=13 '{ 
{if (NR == LINENUM) sub(OLDSTRING,NEWSTRING)} print $0 }'  filename

Thanx for ur solution.
The code u provided only replaces the first occurence of the string on that line not the other occurences. how is that possible.
Please reply soon.

This will replace text matching "edcba" at position 45 of each line (if there are multiple records) with text "abcde" and output to a second file called "newfile".
------------
awk ' BEGIN{
while (getline i < "filename"){

string=substr(i,45,5)

if (string == "edcba"){

print substr(i,1,44) "abcde" substr(i,50,length(i)-49) > "newfile"

}
}
} ' filename
----------
I don't know if that works for your application. If not, do research on "sed".

modify sub to gsub to replace all occurences.

Hi I want to replace the string Additional Text to rawText in my file...But not sure which linenum it will come everytime....
But it is one tim eoccurence in the file..I such cases how to replace the string without line number..