here-docs.html

BASH Shell 编程 经典教程 《高级SHELL脚本编程》中文版

  5 RESPONDENT="the author of this fine script"  
  6 
  7 cat <<'Endofmessage'
  8 
  9 Hello, there, $NAME.
 10 Greetings to you, $NAME, from $RESPONDENT.
 11 
 12 Endofmessage
 13 
 14 #  如果"limit string"被引用或转义的话, 那么就禁用了参数替换. 
 15 #  下边的两种方式具有相同的效果. 
 16 #  cat <<"Endofmessage"
 17 #  cat <<\Endofmessage
 18 
 19&nbsp;exit 0</PRE
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><HR></DIV
><P
>禁用了参数替换后, 将允许输出文本本身(译者注: 就是未转义的原文). 
        如果你想产生脚本甚至是程序代码的话, 那么可以使用这种办法. </P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="GENERATESCRIPT"
></A
><P
><B
>例子 17-8. 生成另外一个脚本的脚本</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>  1&nbsp;#!/bin/bash
  2&nbsp;# generate-script.sh
  3&nbsp;# 这个脚本的诞生基于Albert Reiner的一个主意. 
  4&nbsp;
  5&nbsp;OUTFILE=generated.sh         # 所产生文件的名字. 
  6&nbsp;
  7&nbsp;
  8&nbsp;# -----------------------------------------------------------
  9&nbsp;# 'Here document包含了需要产生的脚本的代码. 
 10&nbsp;(
 11&nbsp;cat &#60;&#60;'EOF'
 12&nbsp;#!/bin/bash
 13&nbsp;
 14&nbsp;echo "This is a generated shell script."
 15&nbsp;#  Note that since we are inside a subshell,
 16&nbsp;#+ we can't access variables in the "outside" script.
 17&nbsp;
 18&nbsp;echo "Generated file will be named: $OUTFILE"
 19&nbsp;#  Above line will not work as normally expected
 20&nbsp;#+ because parameter expansion has been disabled.
 21&nbsp;#  Instead, the result is literal output.
 22&nbsp;
 23&nbsp;a=7
 24&nbsp;b=3
 25&nbsp;
 26&nbsp;let "c = $a * $b"
 27&nbsp;echo "c = $c"
 28&nbsp;
 29&nbsp;exit 0
 30&nbsp;EOF
 31&nbsp;) &#62; $OUTFILE
 32&nbsp;# -----------------------------------------------------------
 33&nbsp;
 34&nbsp;#  将'limit string'引用起来将会阻止上边
 35&nbsp;#+ here document消息体中的变量扩展. 
 36&nbsp;#  这会使得输出文件中的内容保持here document消息体中的原文. 
 37&nbsp;
 38&nbsp;if [ -f "$OUTFILE" ]
 39&nbsp;then
 40&nbsp;  chmod 755 $OUTFILE
 41&nbsp;  # 让所产生的文件具有可执行权限. 
 42&nbsp;else
 43&nbsp;  echo "Problem in creating file: \"$OUTFILE\""
 44&nbsp;fi
 45&nbsp;
 46&nbsp;#  这个方法也可以用来产生
 47&nbsp;#+ C程序代码, Perl程序代码, Python程序代码, makefile, 
 48&nbsp;#+ 和其他的一些类似的代码. 
 49&nbsp;#  (译者注: 中间一段没译的注释将会被here document打印出来)
 50&nbsp;exit 0</PRE
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><P
>        也可以将here document的输出保存到变量中. 
	<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>  1&nbsp;variable=$(cat &#60;&#60;SETVAR
  2&nbsp;This variable
  3&nbsp;runs over multiple lines.
  4&nbsp;SETVAR)
  5&nbsp;
  6&nbsp;echo "$variable"</PRE
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>
      </P
><P
>A here document can supply input to a function in the same
        script.</P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="HF"
></A
><P
><B
>例子 17-9. Here document与函数</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>  1&nbsp;#!/bin/bash
  2&nbsp;# here-function.sh
  3&nbsp;
  4&nbsp;GetPersonalData ()
  5&nbsp;{
  6&nbsp;  read firstname
  7&nbsp;  read lastname
  8&nbsp;  read address
  9&nbsp;  read city 
 10&nbsp;  read state 
 11&nbsp;  read zipcode
 12&nbsp;} # 这个函数看起来就是一个交互函数, 但是... 
 13&nbsp;
 14&nbsp;
 15&nbsp;# 给上边的函数提供输入.
 16&nbsp;GetPersonalData &#60;&#60;RECORD001
 17&nbsp;Bozo
 18&nbsp;Bozeman
 19&nbsp;2726 Nondescript Dr.
 20&nbsp;Baltimore
 21&nbsp;MD
 22&nbsp;21226
 23&nbsp;RECORD001
 24&nbsp;
 25&nbsp;
 26&nbsp;echo
 27&nbsp;echo "$firstname $lastname"
 28&nbsp;echo "$address"
 29&nbsp;echo "$city, $state $zipcode"
 30&nbsp;echo
 31&nbsp;
 32&nbsp;exit 0</PRE
></FONT
></TD
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><HR></DIV
><P
><A
NAME="ANONHEREDOC0"
></A
></P
><P
>也可以这么使用<SPAN
CLASS="TOKEN"
>:</SPAN
>(冒号), 
			  做一个假命令来从一个here document中接收输出. 
        这么做事实上就是创建了一个<SPAN
CLASS="QUOTE"
>"匿名"</SPAN
>的here document. 
	</P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="ANONHEREDOC"
></A
><P
><B
>例子 17-10. <SPAN
CLASS="QUOTE"
>"匿名"</SPAN
>的here Document</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>  1&nbsp;#!/bin/bash
  2&nbsp;
  3&nbsp;: &#60;&#60;TESTVARIABLES
  4&nbsp;${HOSTNAME?}${USER?}${MAIL?}  # 如果其中某个变量没被设置, 那么就打印错误信息. 
  5&nbsp;TESTVARIABLES
  6&nbsp;
  7&nbsp;exit 0</PRE
></FONT
></TD
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></TABLE
><HR></DIV
><P
><A
NAME="CBLOCK1"
></A
></P
><DIV
CLASS="TIP"
><P
></P
><TABLE
CLASS="TIP"
WIDTH="100%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="./images/tip.gif"
HSPACE="5"
ALT="Tip"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>上边所示技术的一种变化, 可以用来<SPAN
CLASS="QUOTE"
>"注释"</SPAN
>掉代码块. </P
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="COMMENTBLOCK"
></A
><P
><B
>例子 17-11. 注释掉一段代码块</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>  1&nbsp;#!/bin/bash
  2&nbsp;# commentblock.sh
  3&nbsp;
  4&nbsp;: &#60;&#60;COMMENTBLOCK
  5&nbsp;echo "This line will not echo."
  6&nbsp;This is a comment line missing the "#" prefix.
  7&nbsp;This is another comment line missing the "#" prefix.
  8&nbsp;
  9&nbsp;&#38;*@!!++=
 10&nbsp;The above line will cause no error message,
 11&nbsp;because the Bash interpreter will ignore it.
 12&nbsp;COMMENTBLOCK
 13&nbsp;
 14&nbsp;echo "Exit value of above \"COMMENTBLOCK\" is $?."   # 0
 15&nbsp;# 这里将不会显示任何错误. 
 16&nbsp;
 17&nbsp;
 18&nbsp;#  上边的这种技术当然也可以用来注释掉
 19&nbsp;#+ 一段正在使用的代码, 如果你有某些特定调试要求的话. 
 20&nbsp;#  这比在每行前边都敲入"#"来得方便的多, 
 21&nbsp;#+ 而且如果你想恢复的话, 还得将添加上的"#"删除掉. 
 22&nbsp;
 23&nbsp;: &#60;&#60;DEBUGXXX
 24&nbsp;for file in *
 25&nbsp;do
 26&nbsp; cat "$file"
 27&nbsp;done
 28&nbsp;DEBUGXXX
 29&nbsp;
 30&nbsp;exit 0</PRE
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><HR></DIV
><DIV
CLASS="TIP"
><P
></P
><TABLE
CLASS="TIP"
WIDTH="100%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="./images/tip.gif"
HSPACE="5"
ALT="Tip"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>关于这种小技巧的另一个应用就是能够产生<SPAN
CLASS="QUOTE"
>"自文档化(self-documenting)"</SPAN
>的脚本. </P
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="SELFDOCUMENT"
></A
><P
><B
>例子 17-12. 一个自文档化(self-documenting)的脚本</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>  1&nbsp;#!/bin/bash
  2&nbsp;# self-document.sh: 自文档化(self-documenting)的脚本
  3&nbsp;# 修改于"colm.sh".
  4&nbsp;
  5&nbsp;DOC_REQUEST=70
  6&nbsp;
  7&nbsp;if [ "$1" = "-h"  -o "$1" = "--help" ]     # 请求帮助. 
  8&nbsp;then
  9&nbsp;  echo; echo "Usage: $0 [directory-name]"; echo
 10&nbsp;  sed --silent -e '/DOCUMENTATIONXX$/,/^DOCUMENTATIONXX$/p' "$0" |
 11&nbsp;  sed -e '/DOCUMENTATIONXX$/d'; exit $DOC_REQUEST; fi
 12&nbsp;
 13&nbsp;
 14&nbsp;: &#60;&#60;DOCUMENTATIONXX
 15&nbsp;List the statistics of a specified directory in tabular format.
 16&nbsp;---------------------------------------------------------------
 17&nbsp;The command line parameter gives the directory to be listed.
 18&nbsp;If no directory specified or directory specified cannot be read,
 19&nbsp;then list the current working directory.
 20&nbsp;
 21&nbsp;DOCUMENTATIONXX
 22&nbsp;
 23&nbsp;if [ -z "$1" -o ! -r "$1" ]
 24&nbsp;then
 25&nbsp;  directory=.
 26&nbsp;else
 27&nbsp;  directory="$1"
 28&nbsp;fi  
 29&nbsp;
 30&nbsp;echo "Listing of "$directory":"; echo
 31&nbsp;(printf "PERMISSIONS LINKS OWNER GROUP SIZE MONTH DAY HH:MM PROG-NAME\n" \
 32&nbsp;; ls -l "$directory" | sed 1d) | column -t
 33&nbsp;
 34&nbsp;exit 0</PRE
></FONT
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><HR></DIV
><P
>使用<A
HREF="here-docs.html#CATSCRIPTREF"
>cat脚本</A
>也能够完成相同的目的. </P
><P
>      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>  1&nbsp;DOC_REQUEST=70
  2&nbsp;
  3&nbsp;if [ "$1" = "-h"  -o "$1" = "--help" ]     # 请求帮助. 
  4&nbsp;then                                       # 使用"cat脚本" . . . 
  5&nbsp;  cat &#60;&#60;DOCUMENTATIONXX
  6&nbsp;List the statistics of a specified directory in tabular format.
  7&nbsp;---------------------------------------------------------------
  8&nbsp;The command line parameter gives the directory to be listed.
  9&nbsp;If no directory specified or directory specified cannot be read,
 10&nbsp;then list the current working directory.
 11&nbsp;
 12&nbsp;DOCUMENTATIONXX
 13&nbsp;exit $DOC_REQUEST
 14&nbsp;fi</PRE
></FONT
></TD
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>
      </P
><P
>请参考<A
HREF="contributed-scripts.html#ISSPAMMER2"
>例子 A-28</A
>可以看到更多关于<SPAN
CLASS="QUOTE"
>"自文档化"</SPAN
>脚本的好例子. </P
><DIV
CLASS="NOTE"
><P
></P
><TABLE
CLASS="NOTE"
WIDTH="100%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="./images/note.gif"
HSPACE="5"
ALT="Note"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>Here document创建临时文件, 
			  但是这些文件将在打开后被删除, 
			  并且不能够被任何其他进程所访问. 
	    </P
><P
>	      <TABLE
BORDER="1"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="SCREEN"
><SAMP
CLASS="PROMPT"
>bash$ </SAMP
><KBD
CLASS="USERINPUT"
>bash -c 'lsof -a -p $$ -d0' &#60;&#60; EOF</KBD
>
<SAMP
CLASS="PROMPT"
>&#62; </SAMP
><KBD
CLASS="USERINPUT"
>EOF</KBD
>
<SAMP
CLASS="COMPUTEROUTPUT"
>lsof    1213 bozo    0r   REG    3,5    0 30386 /tmp/t1213-0-sh (deleted)</SAMP
>
	      </PRE
></FONT
></TD
></TR
></TABLE
>
	  </P
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="CAUTION"
><P
></P
><TABLE
CLASS="CAUTION"
WIDTH="100%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="./images/caution.gif"
HSPACE="5"
ALT="Caution"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>某些工具是不能放入<EM
>here document</EM
>中运行的. </P
></TD
></TR
></TABLE
></DIV
><P
><A
NAME="INDENTEDLS"
></A
></P
><DIV
CLASS="WARNING"
><P
></P
><TABLE
CLASS="WARNING"
WIDTH="100%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="./images/warning.gif"
HSPACE="5"
ALT="Warning"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>结尾的<EM
>limit string</EM
>, 
	  就是here document最后一行的limit string, 
	  必须从<EM
>第一个</EM
>字符开始. 
	  它的前面不能够有任何<EM
>前置的空白</EM
>. 
	  而在这个limit string后边的空白也会引起异常. 
	  空白将会阻止limit string的识别. 
	  (译者注: 下边这个脚本由于结束limit string的问题, 
	  造成脚本无法结束, 所有内容全部被打印出来, 
	  所以注释就不译了, 保持这个例子脚本的原样.)
  </P
><P
>	 <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>  1&nbsp;#!/bin/bash
  2&nbsp;
  3&nbsp;echo "----------------------------------------------------------------------"
  4&nbsp;
  5&nbsp;cat &#60;&#60;LimitString
  6&nbsp;echo "This is line 1 of the message inside the here document."
  7&nbsp;echo "This is line 2 of the message inside the here document."
  8&nbsp;echo "This is the final line of the message inside the here document."
  9&nbsp;     LimitString
 10&nbsp;#^^^^Indented limit string. Error! This script will not behave as expected.
 11&nbsp;
 12&nbsp;echo "----------------------------------------------------------------------"
 13&nbsp;
 14&nbsp;#  These comments are outside the 'here document',
 15&nbsp;#+ and should not echo.
 16&nbsp;
 17&nbsp;echo "Outside the here document."
 18&nbsp;
 19&nbsp;exit 0
 20&nbsp;
 21&nbsp;echo "This line had better not echo."  # Follows an 'exit' command.</PRE
></FONT
></TD
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></TABLE
>
	 </P
></TD
></TR
></TABLE
></DIV
><P
>对于那些使用<SPAN
CLASS="QUOTE"
>"here document"</SPAN
>, 并且非常复杂的任务, 
		  最好考虑使用<B
CLASS="COMMAND"
>expect</B
>脚本语言, 
		  这种语言就是为了达到向交互程序添加输入的目的而量身定做的. 
	  </P
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><A
HREF="redirapps.html"
ACCESSKEY="P"
>前一页</A
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>重定向的应用</TD
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