filearchiv.html

Shall高级编程

  49     then
  50       filename[n]=$( echo ${record[$n]} | awk '{ print $2 }' )
  51       #  md5sum writes records backwards,
  52       #+ checksum first, then filename.
  53       checksum[n]=$( md5sum "${filename[n]}" )
  54 
  55 
  56       if [ "${record[n]}" = "${checksum[n]}" ]
  57       then
  58         echo "${filename[n]} unchanged."
  59 
  60       elif [ "`basename ${filename[n]}`" != "$dbfile" ]
  61              #  Skip over checksum database file,
  62              #+ as it will change with each invocation of script.
  63 	     #  ---
  64 	     #  This unfortunately means that when running
  65 	     #+ this script on $PWD, tampering with the
  66 	     #+ checksum database file will not be detected.
  67 	     #  Exercise: Fix this.
  68 	then
  69           echo "${filename[n]} : CHECKSUM ERROR!"
  70         # File has been changed since last checked.
  71       fi
  72 
  73       fi
  74 
  75 
  76 
  77     let "n+=1"
  78   done <"$dbfile"       # Read from checksum database file. 
  79 
  80 }  
  81 
  82 # =================================================== #
  83 # main ()
  84 
  85 if [ -z  "$1" ]
  86 then
  87   directory="$PWD"      #  If not specified,
  88 else                    #+ use current working directory.
  89   directory="$1"
  90 fi  
  91 
  92 clear                   # Clear screen.
  93 echo " Running file integrity check on $directory"
  94 echo
  95 
  96 # ------------------------------------------------------------------ #
  97   if [ ! -r "$dbfile" ] # Need to create database file?
  98   then
  99     echo "Setting up database file, \""$directory"/"$dbfile"\"."; echo
 100     set_up_database
 101   fi  
 102 # ------------------------------------------------------------------ #
 103 
 104 check_database          # Do the actual work.
 105 
 106 echo 
 107 
 108 #  You may wish to redirect the stdout of this script to a file,
 109 #+ especially if the directory checked has many files in it.
 110 
 111 exit 0
 112 
 113 #  For a much more thorough file integrity check,
 114 #+ consider the "Tripwire" package,
 115 #+ http://sourceforge.net/projects/tripwire/.
 116&nbsp;</PRE
></TD
></TR
></TABLE
><HR></DIV
><P
>Also see <A
HREF="contributed-scripts.html#DIRECTORYINFO"
>Example A-20</A
>, <A
HREF="colorizing.html#HORSERACE"
>Example 33-14</A
>, and <A
HREF="string-manipulation.html#RANDSTRING"
>Example 9-11</A
> for
	    creative uses of the <B
CLASS="COMMAND"
>md5sum</B
> command.</P
><DIV
CLASS="NOTE"
><TABLE
CLASS="NOTE"
WIDTH="90%"
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
>	    There have been reports that the 128-bit
	    <B
CLASS="COMMAND"
>md5sum</B
> can be cracked, so the more secure
	    160-bit <B
CLASS="COMMAND"
>sha1sum</B
> is a welcome new addition
	    to the checksum toolkit.
          </P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>md5sum testfile</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>e181e2c8720c60522c4c4c981108e367  testfile</TT
>
 
 
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>sha1sum testfile</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>5d7425a9c08a66c3177f1e31286fa40986ffc996  testfile</TT
>
 	      </PRE
></TD
></TR
></TABLE
></TD
></TR
></TABLE
></DIV
><P
>Security consultants have demonstrated that even
	      <B
CLASS="COMMAND"
>sha1sum</B
> can be compromised. Fortunately,
	      newer Linux distros include longer bit-length
	      <B
CLASS="COMMAND"
>sha224sum</B
>,
	      <B
CLASS="COMMAND"
>sha256sum</B
>,
	      <B
CLASS="COMMAND"
>sha384sum</B
>, and
	      <B
CLASS="COMMAND"
>sha512sum</B
> commands.</P
></DD
><DT
><A
NAME="SHREDREF"
></A
><B
CLASS="COMMAND"
>shred</B
></DT
><DD
><P
>Securely erase a file by overwriting it multiple times with
	      random bit patterns before deleting it. This command has
	      the same effect as <A
HREF="extmisc.html#BLOTOUT"
>Example 15-58</A
>, but does it
	      in a more thorough and elegant manner.</P
><P
>This is one of the GNU
	    <I
CLASS="FIRSTTERM"
>fileutils</I
>.</P
><DIV
CLASS="CAUTION"
><TABLE
CLASS="CAUTION"
WIDTH="90%"
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
>Advanced forensic technology may still be able to
	      recover the contents of a file, even after application of
	      <B
CLASS="COMMAND"
>shred</B
>.</P
></TD
></TR
></TABLE
></DIV
></DD
><DT
><A
NAME="UUENCODEREF"
></A
><B
CLASS="COMMAND"
>uuencode</B
></DT
><DD
><P
>This utility encodes binary files (images, sound files,
	      compressed files, etc.) into ASCII characters, making them
	      suitable for transmission in the body of an e-mail message or in a
	      newsgroup posting. This is especially useful where MIME
	      (multimedia) encoding is not available.</P
></DD
><DT
><A
NAME="UUDECODEREF"
></A
><B
CLASS="COMMAND"
>uudecode</B
></DT
><DD
><P
>This reverses the encoding, decoding
	      <I
CLASS="FIRSTTERM"
>uuencoded</I
> files back into the
	      original binaries.</P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="EX52"
></A
><P
><B
>Example 15-38. Uudecoding encoded files</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# Uudecodes all uuencoded files in current working directory.
   3&nbsp;
   4&nbsp;lines=35        # Allow 35 lines for the header (very generous).
   5&nbsp;
   6&nbsp;for File in *   # Test all the files in $PWD.
   7&nbsp;do
   8&nbsp;  search1=`head -n $lines $File | grep begin | wc -w`
   9&nbsp;  search2=`tail -n $lines $File | grep end | wc -w`
  10&nbsp;  #  Uuencoded files have a "begin" near the beginning,
  11&nbsp;  #+ and an "end" near the end.
  12&nbsp;  if [ "$search1" -gt 0 ]
  13&nbsp;  then
  14&nbsp;    if [ "$search2" -gt 0 ]
  15&nbsp;    then
  16&nbsp;      echo "uudecoding - $File -"
  17&nbsp;      uudecode $File
  18&nbsp;    fi  
  19&nbsp;  fi
  20&nbsp;done  
  21&nbsp;
  22&nbsp;#  Note that running this script upon itself fools it
  23&nbsp;#+ into thinking it is a uuencoded file,
  24&nbsp;#+ because it contains both "begin" and "end".
  25&nbsp;
  26&nbsp;#  Exercise:
  27&nbsp;#  --------
  28&nbsp;#  Modify this script to check each file for a newsgroup header,
  29&nbsp;#+ and skip to next if not found.
  30&nbsp;
  31&nbsp;exit 0</PRE
></TD
></TR
></TABLE
><HR></DIV
><DIV
CLASS="TIP"
><TABLE
CLASS="TIP"
WIDTH="90%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="common/tip.png"
HSPACE="5"
ALT="Tip"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>The <A
HREF="textproc.html#FOLDREF"
>fold -s</A
> command
	    may be useful (possibly in a pipe) to process long uudecoded
	    text messages downloaded from Usenet newsgroups.</P
></TD
></TR
></TABLE
></DIV
></DD
><DT
><A
NAME="MIMENCODEREF"
></A
><B
CLASS="COMMAND"
>mimencode</B
>, <A
NAME="MMENCODEREF"
></A
><B
CLASS="COMMAND"
>mmencode</B
></DT
><DD
><P
>The <B
CLASS="COMMAND"
>mimencode</B
> and
	      <B
CLASS="COMMAND"
>mmencode</B
> commands process
	      multimedia-encoded e-mail attachments. Although
	      <I
CLASS="FIRSTTERM"
>mail user agents</I
> (such as
	      <I
CLASS="FIRSTTERM"
>pine</I
> or <I
CLASS="FIRSTTERM"
>kmail</I
>)
	      normally handle this automatically, these particular
	      utilities permit manipulating such attachments manually from
	      the command line or in <A
HREF="timedate.html#BATCHPROCREF"
>batch
	      processing mode</A
> by means of a shell script.</P
></DD
><DT
><A
NAME="CRYPTREF"
></A
><B
CLASS="COMMAND"
>crypt</B
></DT
><DD
><P
>At one time, this was the standard UNIX file encryption
	      utility.

              <A
NAME="AEN11881"
HREF="#FTN.AEN11881"
>[3]</A
>

	      Politically motivated government regulations
	      prohibiting the export of encryption software resulted
	      in the disappearance of <B
CLASS="COMMAND"
>crypt</B
>
	      from much of the UNIX world, and it is still
	      missing from most Linux distributions. Fortunately,
	      programmers have come up with a number of decent
	      alternatives to it, among them the author's very own <A
HREF="ftp://metalab.unc.edu/pub/Linux/utils/file/cruft-0.2.tar.gz"
TARGET="_top"
>cruft</A
>
	      (see <A
HREF="contributed-scripts.html#ENCRYPTEDPW"
>Example A-4</A
>).  </P
></DD
></DL
></DIV
><DIV
CLASS="VARIABLELIST"
><P
><B
><A
NAME="FAMISC1"
></A
>Miscellaneous</B
></P
><DL
><DT
><A
NAME="MKTEMPREF"
></A
><B
CLASS="COMMAND"
>mktemp</B
></DT
><DD
><P
>Create a <I
CLASS="FIRSTTERM"
>temporary file</I
>

	       <A
NAME="AEN11903"
HREF="#FTN.AEN11903"
>[4]</A
>

	      with a <SPAN
CLASS="QUOTE"
>"unique"</SPAN
> filename. When invoked
	      from the command line without additional arguments,
	      it creates a zero-length file in the <TT
CLASS="FILENAME"
>/tmp</TT
> directory.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>mktemp</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>/tmp/tmp.zzsvql3154</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	    </P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;PREFIX=filename
   2&nbsp;tempfile=`mktemp $PREFIX.XXXXXX`
   3&nbsp;#                        ^^^^^^ Need at least 6 placeholders
   4&nbsp;#+                              in the filename template.
   5&nbsp;#   If no filename template supplied,
   6&nbsp;#+ "tmp.XXXXXXXXXX" is the default.
   7&nbsp;
   8&nbsp;echo "tempfile name = $tempfile"
   9&nbsp;# tempfile name = filename.QA2ZpY
  10&nbsp;#                 or something similar...
  11&nbsp;
  12&nbsp;#  Creates a file of that name in the current working directory
  13&nbsp;#+ with 600 file permissions.
  14&nbsp;#  A "umask 177" is therefore unnecessary,
  15&nbsp;#+ but it's good programming practice anyhow.</PRE
></TD
></TR
></TABLE
></P
></DD
><DT
><A
NAME="MAKEREF"
></A
><B
CLASS="COMMAND"
>make</B
></DT
><DD
><P
><A
NAME="MAKEFILEREF"
></A
></P
><P
>Utility for building and compiling binary packages. 
	      This can also be used for any set of operations that is
	      triggered by incremental changes in source files.</P
><P
>The <B
CLASS="COMMAND"
>make</B
> command checks a
	    <TT
CLASS="FILENAME"
>Makefile</TT
>, a list of file dependencies and
	      operations to be carried out.</P
><P
>The <I
CLASS="FIRSTTERM"
>make</I
> utility is, in effect,
	      a powerful scripting language similar in many ways to
	      <I
CLASS="FIRSTTERM"
>Bash</I
>, but with the capability of
	      recognizing <I
CLASS="FIRSTTERM"
>dependencies</I
>. For in-depth
	      coverage of this useful tool set, see the <A
HREF="http://www.gnu.org/manual/manual.html"
TARGET="_top"
>GNU software
	      documentation site</A
>.</P
></DD
><DT
><A
NAME="INSTALLREF"
></A
><B
CLASS="COMMAND"
>install</B
></DT
><DD
><P
>Special purpose file copying command, similar to
	      <B
CLASS="COMMAND"
>cp</B
>, but capable of setting permissions
	      and attributes of the copied files. This command seems
	      tailormade for installing software packages, and as such it
	      shows up frequently in <TT
CLASS="FILENAME"
>Makefiles</TT
>
	      (in the <TT
CLASS="REPLACEABLE"
><I
>make install :</I
></TT
>
	      section). It could likewise find use in installation
	      scripts.</P
></DD
><DT
><A
NAME="DOS2UNIXREF"
></A
><B
CLASS="COMMAND"
>dos2unix</B
></DT
><DD
><P
>This utility, written by Benjamin Lin and collaborators,
	      converts DOS-formatted text files (lines terminated by
	      CR-LF) to UNIX format (lines terminated by LF only),
	      and vice-versa.</P
></DD
><DT
><A
NAME="PTXREF"
></A
><B
CLASS="COMMAND"
>ptx</B
></DT
><DD
><P
>The <B
CLASS="COMMAND"
>ptx [targetfile]</B
> command
	      outputs a permuted index (cross-reference list) of the
	      targetfile. This may be further filtered and formatted in a
	      pipe, if necessary.</P
></DD
><DT
><A
NAME="MOREREF"
></A
><B
CLASS="COMMAND"
>more</B
>, <A
NAME="LESSREF"
></A
><B
CLASS="COMMAND"
>less</B
></DT
><DD
><P
>Pagers that display a text file or stream to
	      <TT
CLASS="FILENAME"
>stdout</TT
>, one screenful at a time.
	      These may be used to filter the output of
	      <TT
CLASS="FILENAME"
>stdout</TT
> . . . or of a script.</P
><P
>	       An interesting application of <B
CLASS="COMMAND"
>more</B
>
	       is to <SPAN
CLASS="QUOTE"
>"test drive"</SPAN
> a command sequence,
	       to forestall potentially unpleasant consequences.
                 <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;ls /home/bozo | awk '{print "rm -rf " $1}' | more
   2&nbsp;#                                            ^^^^
   3&nbsp;		 
   4&nbsp;# Testing the effect of the following (disastrous) command line:
   5&nbsp;#      ls /home/bozo | awk '{print "rm -rf " $1}' | sh
   6&nbsp;#      Hand off to the shell to execute . . .       ^^</PRE
></TD
></TR
></TABLE
>
            </P
></DD
></DL
></DIV
></DIV
><H3
CLASS="FOOTNOTES"
>Notes</H3
><TABLE
BORDER="0"
CLASS="FOOTNOTES"
WIDTH="100%"
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="5%"
><A
NAME="FTN.AEN10910"
HREF="filearchiv.html#AEN10910"
>[1]</A
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="95%"
><P
>An <I
CLASS="FIRSTTERM"
>archive</I
>,
	        in the sense discussed here, is simply a set of related
	        files stored in a single location.</P
></TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="5%"
><A
NAME="FTN.AEN10921"
HREF="filearchiv.html#AEN10921"
>[2]</A
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="95%"
><P
>		    A <B
CLASS="COMMAND"
>tar czvf archive_name.tar.gz *</B
>
		    <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>will</I
></SPAN
> include dotfiles in
		    directories <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>below</I
></SPAN
> the current
		    working directory. This is an undocumented GNU
		    <B
CLASS="COMMAND"
>tar</B
> <SPAN
CLASS="QUOTE"
>"feature"</SPAN
>.
		  </P
></TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="5%"
><A
NAME="FTN.AEN11881