replace local value variable with new value from script
 

I have a file named program1 which has a variable mode and it's value is off.
mode off;

Now i want to write a shell script which will open the program1 file and set the mode to on. Can anyone help me how to do this?

Thank you in advance.

Have a look at the sed command. Information on how to use can be found here

Thank you for the quick response.