sha-bang.html

一本完整的描述Unix Shell 编程的工具书的所有范例

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><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;E_WRONG_ARGS=65
   2&nbsp;script_parameters="-a -h -m -z"
   3&nbsp;#                  -a = all, -h = help, etc.
   4&nbsp;
   5&nbsp;if [ $# -ne $Number_of_expected_args ]
   6&nbsp;then
   7&nbsp;  echo "Usage: `basename $0` $script_parameters"
   8&nbsp;  # `basename $0` is the script's filename.
   9&nbsp;  exit $E_WRONG_ARGS
  10&nbsp;fi</PRE
></TD
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>
      </P
><P
>Many times, you will write a script that carries out one
        particular task. The first script in this chapter is an
        example of this. Later, it might occur to you to generalize
        the script to do other, similar tasks. Replacing the literal
        (<SPAN
CLASS="QUOTE"
>"hard-wired"</SPAN
>) constants by variables is a step in
        that direction, as is replacing repetitive code blocks by <A
HREF="functions.html#FUNCTIONREF"
>functions</A
>.</P
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="INVOKING"
>2.1. Invoking the script</A
></H1
><P
>Having written the script, you can invoke it by <TT
CLASS="USERINPUT"
><B
>sh
	scriptname</B
></TT
>,

	  <A
NAME="AEN223"
HREF="#FTN.AEN223"
>[5]</A
>
	
	or alternatively <TT
CLASS="USERINPUT"
><B
>bash scriptname</B
></TT
>. (Not
	recommended is using <TT
CLASS="USERINPUT"
><B
>sh &#60;scriptname</B
></TT
>,
	since this effectively disables reading from
	<TT
CLASS="FILENAME"
>stdin</TT
> within the script.)	Much more
	convenient is to make the script itself directly executable with
	a <A
HREF="external.html#CHMODREF"
>chmod</A
>.

	<DIV
CLASS="VARIABLELIST"
><DL
><DT
>Either:</DT
><DD
><P
><TT
CLASS="USERINPUT"
><B
>chmod 555 scriptname</B
></TT
> (gives
	      everyone read/execute permission)
	        <A
NAME="AEN236"
HREF="#FTN.AEN236"
>[6]</A
>
	      </P
></DD
><DT
>or</DT
><DD
><P
><TT
CLASS="USERINPUT"
><B
>chmod +rx scriptname</B
></TT
> (gives
	      everyone read/execute permission)</P
><P
><TT
CLASS="USERINPUT"
><B
>chmod
	      u+rx scriptname</B
></TT
> (gives only the
		script owner read/execute permission)</P
></DD
></DL
></DIV
>
      </P
><P
>Having made the script executable, you may now test it by
	<TT
CLASS="USERINPUT"
><B
>./scriptname</B
></TT
>.
	
	  <A
NAME="AEN248"
HREF="#FTN.AEN248"
>[7]</A
>

	If it begins with a <SPAN
CLASS="QUOTE"
>"sha-bang"</SPAN
> line, invoking the
	script calls the correct command interpreter to run it.</P
><P
>As a final step, after testing and debugging,
        you would likely want to move it to <TT
CLASS="FILENAME"
>/usr/local/bin</TT
> (as root, of
        course), to make the script available to yourself and all
        other users as a system-wide executable.  The script could
        then be invoked by simply typing <B
CLASS="COMMAND"
>scriptname</B
>
        <B
CLASS="KEYCAP"
>[ENTER]</B
> from the command line.</P
></DIV
></DIV
><H3
CLASS="FOOTNOTES"
>Notes</H3
><TABLE
BORDER="0"
CLASS="FOOTNOTES"
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><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="5%"
><A
NAME="FTN.AEN152"
HREF="sha-bang.html#AEN152"
>[1]</A
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="95%"
><P
>Some flavors of UNIX (those based on 4.2BSD)
          take a four-byte magic number, requiring
          a blank after the <SPAN
CLASS="TOKEN"
>!</SPAN
> --
          <TT
CLASS="USERINPUT"
><B
>#! /bin/sh</B
></TT
>.</P
></TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="5%"
><A
NAME="FTN.AEN163"
HREF="sha-bang.html#AEN163"
>[2]</A
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="95%"
><P
>The <SPAN
CLASS="TOKEN"
>#!</SPAN
> line in a shell script
	      will be the first thing the command interpreter
	      (<B
CLASS="COMMAND"
>sh</B
> or <B
CLASS="COMMAND"
>bash</B
>)
	      sees. Since this line begins with a <SPAN
CLASS="TOKEN"
>#</SPAN
>,
	      it will be correctly interpreted as a comment when the
	      command interpreter finally executes the script. The
	      line has already served its purpose - calling the command
	      interpreter.</P
><P
>If, in fact, the script includes an
	      <I
CLASS="EMPHASIS"
>extra</I
> <SPAN
CLASS="TOKEN"
>#!</SPAN
> line, then
	      <B
CLASS="COMMAND"
>bash</B
> will interpret it as a comment.
	        <TABLE
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BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;
   3&nbsp;echo "Part 1 of script."
   4&nbsp;a=1
   5&nbsp;
   6&nbsp;#!/bin/bash
   7&nbsp;# This does *not* launch a new script.
   8&nbsp;
   9&nbsp;echo "Part 2 of script."
  10&nbsp;echo $a  # Value of $a stays at 1.</PRE
></TD
></TR
></TABLE
></P
></TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="5%"
><A
NAME="FTN.AEN179"
HREF="sha-bang.html#AEN179"
>[3]</A
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="95%"
><P
>This allows some cute tricks.</P
><P
><TABLE
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BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/rm
   2&nbsp;# Self-deleting script.
   3&nbsp;
   4&nbsp;# Nothing much seems to happen when you run this... except that the file disappears.
   5&nbsp;
   6&nbsp;WHATEVER=65
   7&nbsp;
   8&nbsp;echo "This line will never print (betcha!)."
   9&nbsp;
  10&nbsp;exit $WHATEVER  # Doesn't matter. The script will not exit here.</PRE
></TD
></TR
></TABLE
></P
><P
>Also, try starting a <TT
CLASS="FILENAME"
>README</TT
> file with a
        <TT
CLASS="USERINPUT"
><B
>#!/bin/more</B
></TT
>, and making it executable.
        The result is a self-listing documentation file. (A <A
HREF="here-docs.html#HEREDOCREF"
>here document</A
> using
	<A
HREF="external.html#CATREF"
>cat</A
> is possibly a better alternative
	-- see <A
HREF="here-docs.html#EX71"
>Example 17-3</A
>).</P
></TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="5%"
><A
NAME="FTN.AEN192"
HREF="sha-bang.html#AEN192"
>[4]</A
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="95%"
><P
><A
NAME="POSIX2REF"
></A
><I
CLASS="EMPHASIS"
>P</I
>ortable
	 <I
CLASS="EMPHASIS"
>O</I
>perating
	 <I
CLASS="EMPHASIS"
>S</I
>ystem <I
CLASS="EMPHASIS"
>I</I
>nterface, an attempt to
	 standardize UNI<I
CLASS="EMPHASIS"
>X</I
>-like
	 OSes. The POSIX specifications are listed on the <A
HREF="http://www.opengroup.org/onlinepubs/007904975/toc.htm"
TARGET="_top"
>Open
	 Group site</A
>.</P
></TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="5%"
><A
NAME="FTN.AEN223"
HREF="sha-bang.html#AEN223"
>[5]</A
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="95%"
><P
>Caution: invoking a Bash script by <TT
CLASS="USERINPUT"
><B
>sh
	  scriptname</B
></TT
> turns off Bash-specific extensions, and the
	  script may therefore fail to execute.</P
></TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="5%"
><A
NAME="FTN.AEN236"
HREF="sha-bang.html#AEN236"
>[6]</A
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="95%"
><P
>A script needs <I
CLASS="EMPHASIS"
>read</I
>, as
		well as execute permission for it to run, since the shell
		needs to be able to read it.</P
></TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="5%"
><A
NAME="FTN.AEN248"
HREF="sha-bang.html#AEN248"
>[7]</A
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="95%"
><P
>Why not simply invoke the script with
	  <TT
CLASS="USERINPUT"
><B
>scriptname</B
></TT
>? If the directory you
	  are in (<A
HREF="variables2.html#PWDREF"
>$PWD</A
>) is where
	  <I
CLASS="EMPHASIS"
>scriptname</I
> is located, why doesn't
	  this work? This fails because, for security reasons, the
	  current directory is not by default included in a user's <A
HREF="variables2.html#PATHREF"
>$PATH</A
>. It is therefore necessary to
	  explicitly invoke the script in the current directory with
	  a <TT
CLASS="USERINPUT"
><B
>./scriptname</B
></TT
>.</P
></TD
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