> hello.txt

: > hello.txt

cat > hello.txt

cat > hello.txt
Ubuntu is the
best OS

cat /dev/null > hello.txt

echo "" > hello.txt

xieerqi:$ cat testFile.txt
Filesystem     1K-blocks     Used Available Use% Mounted on
/dev/sda1      115247656 83100492  26269816  76% /
none                   4        0         4   0% /sys/fs/cgroup
udev             2914492        4   2914488   1% /dev
tmpfs             585216     1152    584064   1% /run
none                5120        0      5120   0% /run/lock
none             2926072    98096   2827976   4% /run/shm
none              102400       76    102324   1% /run/user

xieerqi:$ cp /dev/null testFile.txt

xieerqi:$ cat testFile.txt

xieerqi:$

rm hello.txt && touch hello.txt

vi filename -c ':1,$d' -c ':wq'