display manual page descriptions

-m system[,...], --systems=system[,...]
       If this system has access to other operating system's manual page  names,  they  can  be  accessed
       using this option.  To search NewOS's manual page names, use the option -m NewOS.

       The system specified can be a combination of comma delimited operating system names.  To include a
       search of the native operating system's manual page names, include the  system  name  man  in  the
       argument string.  This option will override the $SYSTEM environment variable.

-r, --regex
       Interpret  each  name as a regular expression.  If a name matches any part of a page name, a match
       will be made.  This option causes whatis to be somewhat slower  due  to  the  nature  of  database
       searches.