Linux帮助系统简介

$man date
DATE(1)    User Commands   DATE(1)

NAME
       date - print or set the system date and time

SYNOPSIS
       date [OPTION]... [+FORMAT]
       date [-u|--utc|--universal] [MMDDhhmm[[CC]YY][.ss]]

DESCRIPTION
       Display the current time in the given FORMAT, or set the system date.

       -d, --date=STRING
              display time described by STRING, not `now'
EXAMPLE
       ...
DATE STRING
       ...
AUTHOR
       ...
REPORTING BUGS
       ...
COPYRIGHT
       ...
SEE ALSO
      The full documentation for date is maintained as a Texinfo manual.   If
       the  info  and  date  programs are properly installed at your site, the
       command

              info coreutils 'date invocation'

       should give you access to the complete manual.
 

man -f == whatis
$ whatis date
date (1)             - print or set the system date and time
$ man -f date
date (1)             - print or set the system date and time
man -k == apropos
$ apropos date
asctime (3)          - transform date and time to broken-down time or ASCII
asctime_r (3)        - transform date and time to broken-down time or ASCII
cal (1)              - displays a calendar and the date of Easter
....