Delete lines from text file after copying to a another file

[sandy1028]

vi test.txt

sun
sun
moon
star
moon

 

Now when I execute the command,

 

cat test.txt | grep sun > sun.txt

 

text "sun" is copied to a file.

 

I need a help how to delete the lines which has  "sun" from text.txt and save the file.

 

[steviewdr]

cat text.txt | grep sun > sun.txt | sed -i "/sun/d" text.txt

 

-steve