My code:

```
df -h | sed 's/G/Gb/' >> $2

```

The output: 

```
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda2              29Gb  5.5G   22G  21% /
devtmpfs              757M  196K  757M   1% /dev
tmpfs                 757M  436K  757M   1% /dev/shm

```

The output I need: 

```
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda2              29Gb  5.5Gb   22Gb  21% /
devtmpfs              757M  196K  757M   1% /dev
tmpfs                 757M  436K  757M   1% /dev/shm

```