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線上求助

  1. 大部分指令都有 --help 的選項,但不是所有指令皆有此選項,例如:
    [root@mdk-dyw root]# ls --help
    Usage: ls [OPTION]... [FILE]...
    List information about the FILEs (the current directory by default).
    Sort entries alphabetically if none of -cftuSUX nor --sort.
    
    Mandatory arguments to long options are mandatory for short options too.
      -a, --all                  do not hide entries starting with .
      -A, --almost-all           do not list implied . and ..
          --author               print the author of each file
      -b, --escape               print octal escapes for nongraphic characters
          --block-size=SIZE      use SIZE-byte blocks
      -B, --ignore-backups       do not list implied entries ending with ~
      -c                         with -lt: sort by, and show, ctime (time of last
                                   modification of file status information)
                                   with -l: show ctime and sort by name
                                   otherwise: sort by ctime
      -C                         list entries by columns
          --color[=WHEN]         control whether color is used to distinguish file
                                   types.  WHEN may be `never', `always', or `auto'
      -d, --directory            list directory entries instead of contents,
                                   and do not dereference symbolic links
      -D, --dired                generate output designed for Emacs' dired mode
      -f                         do not sort, enable -aU, disable -lst
      -F, --classify             append indicator (one of */=@|) to entries
          --format=WORD          across -x, commas -m, horizontal -x, long -l,
                                   single-column -1, verbose -l, vertical -C
          --full-time            like -l --time-style=full-iso
      -g                         like -l, but do not list owner
      -G, --no-group             inhibit display of group information
      -h, --human-readable  print sizes in human readable format (e.g., 1K 234M 2G)
          --si                   likewise, but use powers of 1000 not 1024
      -H, --dereference-command-line
                                 follow symbolic links listed on the command line
          --dereference-command-line-symlink-to-dir
                                 follow each command line symbolic link
                                   that points to a directory
          --indicator-style=WORD append indicator with style WORD to entry names:
                                   none (default), classify (-F), file-type (-p)
      -i, --inode                print index number of each file
      -I, --ignore=PATTERN       do not list implied entries matching shell PATTERN
      -k                         like --block-size=1K
      -l                         use a long listing format
      -L, --dereference          when showing file information for a symbolic
                                   link, show information for the file the link
                                   references rather than for the link itself
      -m                         fill width with a comma separated list of entries
      -n, --numeric-uid-gid      like -l, but list numeric UIDs and GIDs
      -N, --literal              print raw entry names (don't treat e.g. control
                                   characters specially)
      -o                         like -l, but do not list group information
      -p, --file-type            append indicator (one of /=@|) to entries
      -q, --hide-control-chars   print ? instead of non graphic characters
          --show-control-chars   show non graphic characters as-is (default
                                 unless program is `ls' and output is a terminal)
      -Q, --quote-name           enclose entry names in double quotes
          --quoting-style=WORD   use quoting style WORD for entry names:
                                   literal, locale, shell, shell-always, c, escape
      -r, --reverse              reverse order while sorting
      -R, --recursive            list subdirectories recursively
      -s, --size                 print size of each file, in blocks
      -S                         sort by file size
          --sort=WORD            extension -X, none -U, size -S, time -t,
                                   version -v
                                 status -c, time -t, atime -u, access -u, use -u
          --time=WORD            show time as WORD instead of modification time:
                                   atime, access, use, ctime or status; use
                                   specified time as sort key if --sort=time
          --time-style=STYLE     show times using style STYLE:
                                   full-iso, long-iso, iso, locale, +FORMAT
                                 FORMAT is interpreted like `date'; if FORMAT is
                                 FORMAT1<newline>FORMAT2, FORMAT1 applies to
                                 non-recent files and FORMAT2 to recent files;
                                 if STYLE is prefixed with `posix-', STYLE
                                 takes effect only outside the POSIX locale
      -t                         sort by modification time
      -T, --tabsize=COLS         assume tab stops at each COLS instead of 8
      -u                         with -lt: sort by, and show, access time
                                   with -l: show access time and sort by name
                                   otherwise: sort by access time
      -U                         do not sort; list entries in directory order
      -v                         sort by version
      -w, --width=COLS           assume screen width instead of current value
      -x                         list entries by lines instead of by columns
      -X                         sort alphabetically by entry extension
      -1                         list one file per line
          --help     display this help and exit
          --version  output version information and exit
    
    SIZE may be (or may be an integer optionally followed by) one of following:
    kB 1000, K 1024, MB 1000*1000, M 1024*1024, and so on for G, T, P, E, Z, Y.
    
    By default, color is not used to distinguish types of files.  That is
    equivalent to using --color=none.  Using the --color option without the
    optional WHEN argument is equivalent to using --color=always.  With
    --color=auto, color codes are output only if standard output is connected
    to a terminal (tty).
    
    Report bugs to <bug-coreutils@gnu.org>.
    

  2. 其他基本指令之 -help 功能:
    1. date - page [*]:顯示日期及時間。
    2. cal - page [*]:顯示日月曆。
    3. bc - page [*]:簡單好用的計算機。

  3. 一般指令之 -help 選項可能提供:
    1. 指令使用方法;
    2. 選項之用途;
    3. 若選項需要加入參數,則說明參數之格式;
    4. 簡易說明。

練習題

  1. 一般 Linux 指令提供功能查詢之選項為何?
    Sol. -help
  2. 所有 Linux 指令皆提供選項 -help 以查詢指令用法?
    Sol. 錯。
  3. Linux 指令若有選項 -help,至少可提供?
    Sol. 指令用法與選項用途。



2017-07-03