Replace Lines with Given Strings in Shell

Let's learn how to replace given lines by given string. Consider, for example,

$ cat some_file

abcdefg

hijklmn

opqrstu

vwxyz

12345

67890

Let's replace line 2 with string THIS_IS_NEW_LINE2

$ sed '2s/.*/THIS_IS_NEW_LINE2/g' some_file

abcdefg

THIS_IS_NEW_LINE2

opqrstu

vwxyz

12345

67890

You can replace multiple lines with multiple -e options

$ sed -e '2s/.*/THIS_IS_NEW_LINE2/g' -e '3s/.*/THIS_IS_NEW_LINE3/g' some_file

abcdefg

THIS_IS_NEW_LINE2

THIS_IS_NEW_LINE3

vwxyz

12345

67890

Of course, you can always use -i option to modify file on the fly

$ sed -i '2s/.*/THIS_IS_NEW_LINE2/g' some_file

$ cat some_file

abcdefg

THIS_IS_NEW_LINE2

opqrstu

vwxyz

12345

67890