# cat emaillist
shahzad@example.com
shahzad.in@example.com
shahzad.out@example.com
alam@example.com
alam.out@example.com
Delete any matched keyword form file. I am deleting here .in@example.com
Use following sed command:
# sed '/.in@example.com/d' emaillist
Output:
shahzad@example.com
shahzad.out@example.com
alam@example.com
Redirect output in new file
# sed '/.in@example.com/d' emaillist >emailnew
# cat emailnew
shahzad@example.com
shahzad.out@example.com
alam@example.com
Delete keyword using –I option under file
# sed -i '/.in@example.com/d' emaillist
# cat emaillist
shahzad@example.com
shahzad.out@example.com
alam@example.com
alam.out@example.com