extmisc.html

一本完整的描述Unix Shell 编程的工具书的所有范例

>lpr</B
>
	      commands send file(s) to the print queue, to be printed as
	      hard copy.

	      <A
NAME="AEN10453"
HREF="#FTN.AEN10453"
>[2]</A
>

	      These commands trace the origin of their names to the
	      line printers of another era.</P
><P
><TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>lp file1.txt</B
></TT
>
	        or <TT
CLASS="PROMPT"
>bash </TT
><TT
CLASS="USERINPUT"
><B
>lp
		&#60;file1.txt</B
></TT
></P
><P
>It is often useful to pipe the formatted output from
	        <B
CLASS="COMMAND"
>pr</B
> to <B
CLASS="COMMAND"
>lp</B
>.</P
><P
><TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>pr -options file1.txt | lp</B
></TT
>
	        </P
><P
>Formatting packages, such as <B
CLASS="COMMAND"
>groff</B
> and
	        <I
CLASS="EMPHASIS"
>Ghostscript</I
> may send their output
		directly to <B
CLASS="COMMAND"
>lp</B
>.</P
><P
><TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>groff -Tascii file.tr | lp</B
></TT
>
	        </P
><P
><TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>gs -options | lp file.ps</B
></TT
>
	        </P
><P
>Related commands are <B
CLASS="COMMAND"
>lpq</B
>, for viewing
	        the print queue, and <B
CLASS="COMMAND"
>lprm</B
>, for removing
		jobs from the print queue.</P
></DD
><DT
><A
NAME="TEEREF"
></A
><B
CLASS="COMMAND"
>tee</B
></DT
><DD
><P
>[UNIX borrows an idea from the plumbing trade.]</P
><P
>This is a redirection operator, but with a difference. Like the
	      plumber's <SPAN
CLASS="QUOTE"
>"tee,"</SPAN
> it permits <SPAN
CLASS="QUOTE"
>"siponing
              off"</SPAN
> <I
CLASS="EMPHASIS"
>to a file </I
>the output of a command 
	      or commands within a pipe, but without affecting the result. This is
	      useful for printing an ongoing process to a file or paper, perhaps to
	      keep track of it for debugging purposes.</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
>                              (redirection)
                             |----&#62; to file
                             |
   ==========================|====================
   command ---&#62; command ---&#62; |tee ---&#62; command ---&#62; ---&#62; output of pipe
   ===============================================
 	      </PRE
></TD
></TR
></TABLE
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;cat listfile* | sort | tee check.file | uniq &#62; result.file</PRE
></TD
></TR
></TABLE
>
	      (The file <TT
CLASS="FILENAME"
>check.file</TT
> contains
	      the concatenated sorted <SPAN
CLASS="QUOTE"
>"listfiles"</SPAN
>,
	      before the duplicate lines are removed by <A
HREF="textproc.html#UNIQREF"
>uniq</A
>.)</P
></DD
><DT
><B
CLASS="COMMAND"
>mkfifo</B
></DT
><DD
><P
><A
NAME="NAMEDPIPEREF"
></A
>This obscure command
	      creates a <I
CLASS="EMPHASIS"
>named pipe</I
>, a temporary
	      <I
CLASS="EMPHASIS"
>first-in-first-out buffer</I
> for
	      transferring data between processes.

		<A
NAME="AEN10515"
HREF="#FTN.AEN10515"
>[3]</A
>

	      Typically, one process writes to the FIFO, and the other
	      reads from it. See <A
HREF="contributed-scripts.html#FIFO"
>Example A-15</A
>.</P
></DD
><DT
><B
CLASS="COMMAND"
>pathchk</B
></DT
><DD
><P
>This command checks the validity of a filename. If the
	      filename exceeds the maximum allowable length (255
	      characters) or one or more of the directories in
	      its path is not searchable, then an error message
	      results.</P
><P
>Unfortunately, <B
CLASS="COMMAND"
>pathchk</B
> does
	      not return a recognizable error code, and it is therefore
	      pretty much useless in a script. Consider instead the
	      <A
HREF="fto.html#RTIF"
>file test operators</A
>.</P
></DD
><DT
><A
NAME="DDREF"
></A
><B
CLASS="COMMAND"
>dd</B
></DT
><DD
><P
>This is the somewhat obscure and much feared <SPAN
CLASS="QUOTE"
>"data
	      duplicator"</SPAN
> command.  Originally a utility
	      for exchanging data on magnetic tapes between UNIX
	      minicomputers and IBM mainframes, this command still
	      has its uses.  The <B
CLASS="COMMAND"
>dd</B
> command simply
	      copies a file (or <TT
CLASS="FILENAME"
>stdin/stdout</TT
>), but
	      with conversions. Possible conversions are ASCII/EBCDIC,
	        
		<A
NAME="AEN10548"
HREF="#FTN.AEN10548"
>[4]</A
>

	      upper/lower case, swapping of byte pairs between input
	      and output, and skipping and/or truncating the head or
	      tail of the input file. A <TT
CLASS="USERINPUT"
><B
>dd --help</B
></TT
>
	      lists the conversion and other options that this powerful
	      utility takes.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;# Converting a file to all uppercase:
   2&nbsp;
   3&nbsp;dd if=$filename conv=ucase &#62; $filename.uppercase
   4&nbsp;#                    lcase   # For lower case conversion</PRE
></TD
></TR
></TABLE
>
            </P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="SELFCOPY"
></A
><P
><B
>Example 12-52. A script that copies itself</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# self-copy.sh
   3&nbsp;
   4&nbsp;# This script copies itself.
   5&nbsp;
   6&nbsp;file_subscript=copy
   7&nbsp;
   8&nbsp;dd if=$0 of=$0.$file_subscript 2&#62;/dev/null
   9&nbsp;# Suppress messages from dd:   ^^^^^^^^^^^
  10&nbsp;
  11&nbsp;exit $?</PRE
></TD
></TR
></TABLE
><HR></DIV
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="EXERCISINGDD"
></A
><P
><B
>Example 12-53. Exercising <B
CLASS="COMMAND"
>dd</B
></B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# exercising-dd.sh
   3&nbsp;
   4&nbsp;# Script by Stephane Chazelas.
   5&nbsp;# Somewhat modified by document author.
   6&nbsp;
   7&nbsp;input_file=$0   # This script.
   8&nbsp;output_file=log.txt
   9&nbsp;n=3
  10&nbsp;p=5
  11&nbsp;
  12&nbsp;dd if=$input_file of=$output_file bs=1 skip=$((n-1)) count=$((p-n+1)) 2&#62; /dev/null
  13&nbsp;# Extracts characters n to p from this script.
  14&nbsp;
  15&nbsp;# -------------------------------------------------------
  16&nbsp;
  17&nbsp;echo -n "hello world" | dd cbs=1 conv=unblock 2&#62; /dev/null
  18&nbsp;# Echoes "hello world" vertically.
  19&nbsp;
  20&nbsp;exit 0</PRE
></TD
></TR
></TABLE
><HR></DIV
><P
>To demonstrate just how versatile <B
CLASS="COMMAND"
>dd</B
> is,
	     let's use it to capture keystrokes.</P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="DDKEYPRESS"
></A
><P
><B
>Example 12-54. Capturing Keystrokes</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# dd-keypress.sh: Capture keystrokes without needing to press ENTER.
   3&nbsp;
   4&nbsp;
   5&nbsp;keypresses=4                      # Number of keypresses to capture.
   6&nbsp;
   7&nbsp;
   8&nbsp;old_tty_setting=$(stty -g)        # Save old terminal settings.
   9&nbsp;
  10&nbsp;echo "Press $keypresses keys."
  11&nbsp;stty -icanon -echo                # Disable canonical mode.
  12&nbsp;                                  # Disable local echo.
  13&nbsp;keys=$(dd bs=1 count=$keypresses 2&#62; /dev/null)
  14&nbsp;# 'dd' uses stdin, if "if" (input file) not specified.
  15&nbsp;
  16&nbsp;stty "$old_tty_setting"           # Restore old terminal settings.
  17&nbsp;
  18&nbsp;echo "You pressed the \"$keys\" keys."
  19&nbsp;
  20&nbsp;# Thanks, Stephane Chazelas, for showing the way.
  21&nbsp;exit 0</PRE
></TD
></TR
></TABLE
><HR></DIV
><P
>The <B
CLASS="COMMAND"
>dd</B
> command can do random access on a
	      data stream.

	        <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;echo -n . | dd bs=1 seek=4 of=file conv=notrunc
   2&nbsp;# The "conv=notrunc" option means that the output file will not be truncated.		
   3&nbsp;
   4&nbsp;# Thanks, S.C.</PRE
></TD
></TR
></TABLE
>
            </P
><P
>The <B
CLASS="COMMAND"
>dd</B
> command can copy raw data
	      and disk images to and from devices, such as floppies and
	      tape drives (<A
HREF="contributed-scripts.html#COPYCD"
>Example A-5</A
>). A common use is
	      creating boot floppies.</P
><P
>		<TT
CLASS="USERINPUT"
><B
>dd if=kernel-image of=/dev/fd0H1440</B
></TT
>
             </P
><P
>Similarly, <B
CLASS="COMMAND"
>dd</B
> can copy the entire
	       contents of a floppy, even one formatted with a
	       <SPAN
CLASS="QUOTE"
>"foreign"</SPAN
> OS, to the hard drive as an
	       image file.</P
><P
>		<TT
CLASS="USERINPUT"
><B
>dd if=/dev/fd0 of=/home/bozo/projects/floppy.img</B
></TT
>
             </P
><P
>	      Other applications of <B
CLASS="COMMAND"
>dd</B
> include
	      initializing temporary swap files (<A
HREF="zeros.html#EX73"
>Example 28-2</A
>)
	      and ramdisks (<A
HREF="zeros.html#RAMDISK"
>Example 28-3</A
>). It can even do a
	      low-level copy of an entire hard drive partition, although
	      this is not necessarily recommended.</P
><P
>People (with presumably nothing better to do with
	      their time) are constantly thinking of interesting
	      applications of <B
CLASS="COMMAND"
>dd</B
>.</P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="BLOTOUT"
></A
><P
><B
>Example 12-55. Securely deleting a file</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# blot-out.sh: Erase "all" traces of a file.
   3&nbsp;
   4&nbsp;#  This script overwrites a target file alternately
   5&nbsp;#+ with random bytes, then zeros before finally deleting it.
   6&nbsp;#  After that, even examining the raw disk sectors by conventional methods
   7&nbsp;#+ will not reveal the original file data.
   8&nbsp;
   9&nbsp;PASSES=7         #  Number of file-shredding passes.
  10&nbsp;                 #  Increasing this slows script execution,
  11&nbsp;                 #+ especially on large target files.
  12&nbsp;BLOCKSIZE=1      #  I/O with /dev/urandom requires unit block size,
  13&nbsp;                 #+ otherwise you get weird results.
  14&nbsp;E_BADARGS=70     #  Various error exit codes.
  15&nbsp;E_NOT_FOUND=71
  16&nbsp;E_CHANGED_MIND=72
  17&nbsp;
  18&nbsp;if [ -z "$1" ]   # No filename specified.
  19&nbsp;then
  20&nbsp;  echo "Usage: `basename $0` filename"
  21&nbsp;  exit $E_BADARGS
  22&nbsp;fi
  23&nbsp;
  24&nbsp;file=$1
  25&nbsp;
  26&nbsp;if [ ! -e "$file" ]
  27&nbsp;then
  28&nbsp;  echo "File \"$file\" not found."
  29&nbsp;  exit $E_NOT_FOUND
  30&nbsp;fi  
  31&nbsp;
  32&nbsp;echo; echo -n "Are you absolutely sure you want to blot out \"$file\" (y/n)? "
  33&nbsp;read answer
  34&nbsp;case "$answer" in
  35&nbsp;[nN]) echo "Changed your mind, huh?"
  36&nbsp;      exit $E_CHANGED_MIND
  37&nbsp;      ;;
  38&nbsp;*)    echo "Blotting out file \"$file\".";;
  39&nbsp;esac
  40&nbsp;
  41&nbsp;
  42&nbsp;flength=$(ls -l "$file" | awk '{print $5}')  # Field 5 is file length.
  43&nbsp;pass_count=1
  44&nbsp;
  45&nbsp;chmod u+w "$file"   # Allow overwriting/deleting the file.
  46&nbsp;
  47&nbsp;echo
  48&nbsp;
  49&nbsp;while [ "$pass_count" -le "$PASSES" ]
  50&nbsp;do
  51&nbsp;  echo "Pass #$pass_count"
  52&nbsp;  sync         # Flush buffers.
  53&nbsp;  dd if=/dev/urandom of=$file bs=$BLOCKSIZE count=$flength
  54&nbsp;               # Fill with random bytes.
  55&nbsp;  sync         # Flush buffers again.
  56&nbsp;  dd if=/dev/zero of=$file bs=$BLOCKSIZE count=$flength
  57&nbsp;               # Fill with zeros.
  58&nbsp;  sync         # Flush buffers yet again.
  59&nbsp;  let "pass_count += 1"
  60&nbsp;  echo
  61&nbsp;done  
  62&nbsp;
  63&nbsp;
  64&nbsp;rm -f $file    # Finally, delete scrambled and shredded file.
  65&nbsp;sync           # Flush buffers a final time.
  66&nbsp;
  67&nbsp;echo "File \"$file\" blotted out and deleted."; echo
  68&nbsp;
  69&nbsp;
  70&nbsp;exit 0
  71&nbsp;
  72&nbsp;#  This is a fairly secure, if inefficient and slow method
  73&nbsp;#+ of thoroughly "shredding" a file.
  74&nbsp;#  The "shred" command, part of the GNU "fileutils" package,
  75&nbsp;#+ does the same thing, although more efficiently.
  76&nbsp;
  77&nbsp;#  The file cannot not be "undeleted" or retrieved by normal methods.
  78&nbsp;#  However . . .
  79&nbsp;#+ this simple method would *not* likely withstand
  80&nbsp;#+ sophisticated forensic analysis.
  81&nbsp;
  82&nbsp;#  This script may not play well with a journaled file system.
  83&nbsp;#  Exercise (difficult): Fix it so it does.
  84&nbsp;
  85&nbsp;
  86&nbsp;
  87&nbsp;#  Tom Vier's "wipe" file-deletion package does a much more thorough job
  88&nbsp;#+ of file shredding than this simple script.
  89&nbsp;#     http://www.ibiblio.org/pub/Linux/utils/file/wipe-2.0.0.tar.bz2
  90&nbsp;
  91&nbsp;#  For an in-depth analysis on the topic of file deletion and security,
  92&nbsp;#+ see Peter Gutmann's paper,
  93&nbsp;#+     "Secure Deletion of Data From Magnetic and Solid-State Memory".
  94&nbsp;#       http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html</PRE
></TD
></TR
></TABLE
><HR></DIV
></DD
><DT
><A
NAME="ODREF"
></A
><B
CLASS="COMMAND"
>od</B
></DT
><DD
><P
>The <B
CLASS="COMMAND"
>od</B
>, or <I
CLASS="EMPHASIS"
>octal
	      dump</I
> filter converts input (or files) to octal
	      (base-8) or other bases. This is useful for viewing or
	      processing binary data files or otherwise unreadable system
	      device files, such as <TT
CLASS="FILENAME"
>/dev/urandom</TT
>,
	      and as a filter for binary data. See <A
HREF="randomvar.html#SEEDINGRANDOM"
>Example 9-28</A
> and <A
HREF="textproc.html#RND"
>Example 12-13</A
>.</P
></DD
><DT
><B
CLASS="COMMAND"
>hexdump</B
></DT
><DD
><P
>Performs a hexadecimal, octal, decimal, or ASCII
	      dump of a binary file. This command is the rough equivalent
	      of <B
CLASS="COMMAND"
>od</B
>, above, but not nearly as
	      useful.</P
></DD
><DT
><B
CLASS="COMMAND"
>objdump</B
></DT
><DD
><P
>Displays information about an object file or binary
	      executable in either hexadecimal form or as a disassembled
	      listing (with the <TT
CLASS="OPTION"
>-d</TT
> option).</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>objdump -d /bin/ls</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>/bin/ls:     file format elf32-i386

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