descartes@box:~$ touch file.txt
descartes@box:~$ echo A >> file.txt
descartes@box:~$ echo B >> file.txt
descartes@box:~$ echo C >> file.txt
descartes@box:~$ cat file.
file.pcap  file.tx    file.txt
descartes@box:~$ cat file.txt
A
B
C
descartes@box:~$ grep -v B file.txt
A
C
descartes@box:~$ grep -v B file.txt >> file.tmp && mv file.tmp file.txt
descartes@box:~$ cat file.txt
A
C
descartes@box:~$ cat retarded
Thusly, you are retarded.