关于 here document 的用法

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代码:

   Here Documents
       This  type  of  redirection  instructs the shell to read input from the
       current source until a line containing  only  word  (with  no  trailing
       blanks)  is seen.  All of the lines read up to that point are then used
       as the standard input for a command.

       The format of here-documents is:

              <<[-]word
                      here-document
              delimiter

       No parameter expansion, command substitution, arithmetic expansion,  or
       pathname expansion is performed on word.  If any characters in word are
       quoted, the delimiter is the result of quote removal on word,  and  the
       lines  in the here-document are not expanded.  If word is unquoted, all
       lines of the here-document are subjected to parameter  expansion,  com-
       mand  substitution,  and arithmetic expansion.  In the latter case, the
       character sequence \<newline> is ignored, and \ must be used  to  quote
       the characters \, $, and `.

       If the redirection operator is <<-, then all leading tab characters are
       stripped from input lines and  the  line  containing  delimiter.   This
       allows  here-documents within shell scripts to be indented in a natural
       fashion.