here-docs.html

Shall高级编程

  29 
  30 echo "Listing of "$directory":"; echo
  31 (printf "PERMISSIONS LINKS OWNER GROUP SIZE MONTH DAY HH:MM PROG-NAME\n" \
  32 ; ls -l "$directory" | sed 1d) | column -t
  33 
  34&nbsp;exit 0</PRE
></TD
></TR
></TABLE
><HR></DIV
><P
>Using a <A
HREF="here-docs.html#CATSCRIPTREF"
>cat script</A
> is an
        alternate way of accomplishing this.</P
><P
>      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;DOC_REQUEST=70
   2&nbsp;
   3&nbsp;if [ "$1" = "-h"  -o "$1" = "--help" ]     # Request help.
   4&nbsp;then                                       # Use a "cat script" . . .
   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 $DOC_REQUEST
  14&nbsp;fi</PRE
></TD
></TR
></TABLE
>
      </P
><P
>See also <A
HREF="contributed-scripts.html#ISSPAMMER2"
>Example A-30</A
> for one more excellent example
        of a self-documenting script.</P
><P
><A
NAME="HERETEMP"
></A
></P
><DIV
CLASS="NOTE"
><TABLE
CLASS="NOTE"
WIDTH="100%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="common/note.png"
HSPACE="5"
ALT="Note"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>Here documents create temporary files, but these
	    files are deleted after opening and are not accessible to
	    any other process.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>bash -c 'lsof -a -p $$ -d0' &#60;&#60; EOF</B
></TT
>
 <TT
CLASS="PROMPT"
>&#62; </TT
><TT
CLASS="USERINPUT"
><B
>EOF</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>lsof    1213 bozo    0r   REG    3,5    0 30386 /tmp/t1213-0-sh (deleted)</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	  </P
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="CAUTION"
><TABLE
CLASS="CAUTION"
WIDTH="100%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="common/caution.png"
HSPACE="5"
ALT="Caution"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>Some utilities will not work inside a
	  <I
CLASS="FIRSTTERM"
>here document</I
>.</P
></TD
></TR
></TABLE
></DIV
><P
><A
NAME="INDENTEDLS"
></A
></P
><DIV
CLASS="WARNING"
><TABLE
CLASS="WARNING"
WIDTH="100%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="common/warning.png"
HSPACE="5"
ALT="Warning"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>The closing <I
CLASS="FIRSTTERM"
>limit string</I
>,
	  on the final line of a here document, must start in the
	  <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>first</I
></SPAN
> character position. There can
	  be <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>no leading whitespace</I
></SPAN
>. Trailing
	  whitespace after the limit string likewise causes unexpected
	  behavior. The whitespace prevents the limit string from being
	  recognized.</P
><P
>	 <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><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
></TD
></TR
></TABLE
>
	 </P
></TD
></TR
></TABLE
></DIV
><P
>For those tasks too complex for a <SPAN
CLASS="QUOTE"
>"here
	  document"</SPAN
>, consider using the <B
CLASS="COMMAND"
>expect</B
>
	  scripting language, which is specifically tailored for feeding
	  input into interactive programs.</P
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="AEN16438"
></A
>18.1. Here Strings</H1
><P
><A
NAME="HERESTRINGSREF"
></A
></P
><P
>A <I
CLASS="FIRSTTERM"
>here string</I
> can be considered as
	   a stripped-down form of a <I
CLASS="FIRSTTERM"
>here document</I
>.
	   It consists of nothing more than <B
CLASS="COMMAND"
>COMMAND
	   &#60;&#60;&#60;$WORD</B
>, where <TT
CLASS="VARNAME"
>$WORD</TT
>
	   is expanded and fed to the <TT
CLASS="FILENAME"
>stdin</TT
> of
	   <TT
CLASS="PARAMETER"
><I
>COMMAND</I
></TT
>.</P
><P
>As a simple example, consider this alternative to the <A
HREF="internal.html#ECHOGREPREF"
>echo-grep</A
> construction.</P
><P
>	  <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;# Instead of:
   2&nbsp;if echo "$VAR" | grep -q txt   # if [[ $VAR = *txt* ]]
   3&nbsp;# etc.
   4&nbsp;
   5&nbsp;# Try:
   6&nbsp;if grep -q "txt" &#60;&#60;&#60; "$VAR"
   7&nbsp;then
   8&nbsp;   echo "$VAR contains the substring sequence \"txt\""
   9&nbsp;fi
  10&nbsp;# Thank you, Sebastian Kaminski, for the suggestion.</PRE
></TD
></TR
></TABLE
>
        </P
><P
><A
NAME="HSREAD"
></A
></P
><P
>Or, in combination with <A
HREF="internal.html#READREF"
>read</A
>:</P
><P
>	<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;String="This is a string of words."
   2&nbsp;
   3&nbsp;read -r -a Words &#60;&#60;&#60; "$String"
   4&nbsp;#  The -a option to "read"
   5&nbsp;#+ assigns the resulting values to successive members of an array.
   6&nbsp;
   7&nbsp;echo "First word in String is:    ${Words[0]}"   # This
   8&nbsp;echo "Second word in String is:   ${Words[1]}"   # is
   9&nbsp;echo "Third word in String is:    ${Words[2]}"   # a
  10&nbsp;echo "Fourth word in String is:   ${Words[3]}"   # string
  11&nbsp;echo "Fifth word in String is:    ${Words[4]}"   # of
  12&nbsp;echo "Sixth word in String is:    ${Words[5]}"   # words.
  13&nbsp;echo "Seventh word in String is:  ${Words[6]}"   # (null)
  14&nbsp;                                                 # Past end of $String.
  15&nbsp;
  16&nbsp;# Thank you, Francisco Lobo, for the suggestion.</PRE
></TD
></TR
></TABLE
>
        </P
><P
><A
NAME="HSPRE"
></A
></P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="PREPENDEX"
></A
><P
><B
>Example 18-13. Prepending a line to a file</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# prepend.sh: Add text at beginning of file.
   3&nbsp;#
   4&nbsp;#  Example contributed by Kenny Stauffer,
   5&nbsp;#+ and slightly modified by document author.
   6&nbsp;
   7&nbsp;
   8&nbsp;E_NOSUCHFILE=65
   9&nbsp;
  10&nbsp;read -p "File: " file   # -p arg to 'read' displays prompt.
  11&nbsp;if [ ! -e "$file" ]
  12&nbsp;then   # Bail out if no such file.
  13&nbsp;  echo "File $file not found."
  14&nbsp;  exit $E_NOSUCHFILE
  15&nbsp;fi
  16&nbsp;
  17&nbsp;read -p "Title: " title
  18&nbsp;cat - $file &#60;&#60;&#60;$title &#62; $file.new
  19&nbsp;
  20&nbsp;echo "Modified file is $file.new"
  21&nbsp;
  22&nbsp;exit 0
  23&nbsp;
  24&nbsp;# from 'man bash':
  25&nbsp;# Here Strings
  26&nbsp;# 	A variant of here documents, the format is:
  27&nbsp;# 
  28&nbsp;# 		&#60;&#60;&#60;word
  29&nbsp;# 
  30&nbsp;# 	The word is expanded and supplied to the command on its standard input.</PRE
></TD
></TR
></TABLE
><HR></DIV
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="MAILBOXGREP"
></A
><P
><B
>Example 18-14. Parsing a mailbox</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;#  Script by Francisco Lobo,
   3&nbsp;#+ and slightly modified and commented by ABS Guide author.
   4&nbsp;#  Used in ABS Guide with permission. (Thank you!)
   5&nbsp;
   6&nbsp;# This script will not run under Bash versions &#60; 3.0.
   7&nbsp;
   8&nbsp;
   9&nbsp;E_MISSING_ARG=67
  10&nbsp;if [ -z "$1" ]
  11&nbsp;then
  12&nbsp;  echo "Usage: $0 mailbox-file"
  13&nbsp;  exit $E_MISSING_ARG
  14&nbsp;fi
  15&nbsp;
  16&nbsp;mbox_grep()  # Parse mailbox file.
  17&nbsp;{
  18&nbsp;    declare -i body=0 match=0
  19&nbsp;    declare -a date sender
  20&nbsp;    declare mail header value
  21&nbsp;
  22&nbsp;
  23&nbsp;    while IFS= read -r mail
  24&nbsp;#         ^^^^                 Reset $IFS.
  25&nbsp;#  Otherwise "read" will strip leading &#38; trailing space from its input.
  26&nbsp;
  27&nbsp;   do
  28&nbsp;       if [[ $mail =~ "^From " ]]   # Match "From" field in message.
  29&nbsp;       then
  30&nbsp;          (( body  = 0 ))           # "Zero out" variables.
  31&nbsp;          (( match = 0 ))
  32&nbsp;          unset date
  33&nbsp;
  34&nbsp;       elif (( body ))
  35&nbsp;       then
  36&nbsp;            (( match ))
  37&nbsp;            # echo "$mail"
  38&nbsp;            # Uncomment above line if you want entire body of message to display.
  39&nbsp;
  40&nbsp;       elif [[ $mail ]]; then
  41&nbsp;          IFS=: read -r header value &#60;&#60;&#60; "$mail"
  42&nbsp;          #                          ^^^  "here string"
  43&nbsp;
  44&nbsp;          case "$header" in
  45&nbsp;          [Ff][Rr][Oo][Mm] ) [[ $value =~ "$2" ]] &#38;&#38; (( match++ )) ;;
  46&nbsp;          # Match "From" line.
  47&nbsp;          [Dd][Aa][Tt][Ee] ) read -r -a date &#60;&#60;&#60; "$value" ;;
  48&nbsp;          #                                  ^^^
  49&nbsp;          # Match "Date" line.
  50&nbsp;          [Rr][Ee][Cc][Ee][Ii][Vv][Ee][Dd] ) read -r -a sender &#60;&#60;&#60; "$value" ;;
  51&nbsp;          #                                                    ^^^
  52&nbsp;          # Match IP Address (may be spoofed).
  53&nbsp;          esac
  54&nbsp;
  55&nbsp;       else
  56&nbsp;          (( body++ ))
  57&nbsp;          (( match  )) &#38;&#38;
  58&nbsp;          echo "MESSAGE ${date:+of: ${date[*]} }"
  59&nbsp;       #    Entire $date array             ^
  60&nbsp;          echo "IP address of sender: ${sender[1]}"
  61&nbsp;       #    Second field of "Received" line    ^
  62&nbsp;
  63&nbsp;       fi
  64&nbsp;
  65&nbsp;
  66&nbsp;    done &#60; "$1" # Redirect stdout of file into loop.
  67&nbsp;}
  68&nbsp;
  69&nbsp;
  70&nbsp;mbox_grep "$1"  # Send mailbox file to function.
  71&nbsp;
  72&nbsp;exit $?
  73&nbsp;
  74&nbsp;# Exercises:
  75&nbsp;# ---------
  76&nbsp;# 1) Break the single function, above, into multiple functions,
  77&nbsp;#+   for the sake of readability.
  78&nbsp;# 2) Add additional parsing to the script, checking for various keywords.
  79&nbsp;
  80&nbsp;
  81&nbsp;
  82&nbsp;$ mailbox_grep.sh scam_mail
  83&nbsp;  MESSAGE of Thu, 5 Jan 2006 08:00:56 -0500 (EST) 
  84&nbsp;  IP address of sender: 196.3.62.4</PRE
></TD
></TR
></TABLE
><HR></DIV
><P
>Exercise: Find other uses for <I
CLASS="FIRSTTERM"
>here
            strings</I
>.</P
></DIV
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