Now you have to clean up 'a'. And decide whether /tmp or /var/tmp or a dir on some other filesystem has enough space to hold all of 'a' until 'bar' is finished.

Now you have to clean up 'a'. And decide whether /tmp or /var/tmp or a dir on some other filesystem has enough space to hold all of 'a' until 'bar' is finished. Is it a security problem that other processes could snoop the contents of 'a' or even tamper with it?