Cygwin: during sed operation changes are not save

Question

While I'm using sed I'm able to see correct results in terminal but in file changes are not visible.

1. I used following comand:

   sed -e 's/MN2/MN9/g' 01_valid.txt
   

2. on terminal screen I see changes in all lines,

3. but when I execute:

   cat 01_valid.txt
   

4. All changes are gone.

   Operation passes without any errors. Any suggestions?

Answer 1

to save changes in the file, you need -i in insert the changes, other wise it will only change them in stdout

Here is a tutorial to help http://www.grymoire.com/Unix/Sed.html#uh-62h

try sed -i -e 's/MN2/MN9/g' 01_valid.txt