SQL*Plus supports running operating system commands with the HOST command. However, you can't use HOST cd /tmp to change the current working directory. Entering HOST pwd will show that you remained at the original directory. The HOST command worked like it opened a subshell, executed the OS command, then closed the subshell and returned to SQL*Plus.

To change the current working directory, exit from SQL*Plus, cd to the target directory, restart SQL*Plus from there.