Shell Programming and Scripting

Hi *

I've just wanted to ask you if it's possible to modify the input file by using awk.

Let me explain what I need:

I need to change the value $4 from "defaults" to "nodev" in my text file. I've tried to use a string function called "sub" and it works. But I can't figure it out how to change this in my input file ("myfile.txt").

Code:

root@localhost: cat myfile.txt|grep root
/dev/sysvg/root    /   ext3    defaults    1 1

root@localhost: awk '/root/ { sub(/defaults/, "nodev");print } myfile.txt

I know, it can be done by sed command, but I really need to know if it's possible by awk as well.

Thanks in advance

Code:

awk '/root/ { sub(/defaults/, "nodev");print > "myfile.txt"  } myfile.txt

Thanks for you quick response

I know how to redirect the output of this command to the input file. When I use your command above it'll overwrite the whole input file. I just need to overwrite $4 in this file which is mount option "defaults" and only for root filesystem.

myfile.txt="/etc/fstab"

Code:

awk '/root/ { sub(/defaults/, "nodev") } {print > "myfile.txt"} myfile.txt

Great ! Thanks

It works. Could you please explain me why it didn't work without "{ print > "myfile.txt" }".

This code is executed for all the lines in the input file

Code:

{ print > "myfile.txt" }

OK. now it's all clear to me. Thanks