If cmd_prog is a single hyphen ('-'), then instead of executing a program, logsave will take its input from standard input and save it in logfile
logsave is useful for saving the output of initial boot scripts until the /var partition is mounted, so the output can be written to /var/log.
-a This option will cause the output to be appended to logfile , instead of replacing its current contents.
-s This option will cause logsave to skip writing to the log file text which is bracketed with a control-A (ASCII 001 or Start of Header) and control-B (ASCII 002 or Start of Text). This allows progress bar information to be visible to the user on the console, while not being written to the log file.
-v This option will make logsave to be more verbose in its output to the user.