filearchiv.html

Shall高级编程

></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>====
 1:1c
   This is line 1 of "file-1".
 2:1c
   This is line 1 of "file-2".
 3:1c
   This is line 1 of "file-3"</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	      </P
></DD
><DT
><A
NAME="SDIFFREF"
></A
><B
CLASS="COMMAND"
>sdiff</B
></DT
><DD
><P
>Compare and/or edit two files in order to merge
	      them into an output file. Because of its interactive nature,
	      this command would find little use in a script.</P
></DD
><DT
><A
NAME="CMPREF"
></A
><B
CLASS="COMMAND"
>cmp</B
></DT
><DD
><P
>The <B
CLASS="COMMAND"
>cmp</B
> command is a simpler version of
	      <B
CLASS="COMMAND"
>diff</B
>, above. Whereas <B
CLASS="COMMAND"
>diff</B
>
	      reports the differences between two files,
	      <B
CLASS="COMMAND"
>cmp</B
> merely shows at what point they
	      differ.</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
>Like <B
CLASS="COMMAND"
>diff</B
>, <B
CLASS="COMMAND"
>cmp</B
>
	    returns an exit status of 0 if the compared files are
	    identical, and 1 if they differ. This permits use in a test
	    construct within a shell script.</P
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="FILECOMP"
></A
><P
><B
>Example 15-34. Using <I
CLASS="FIRSTTERM"
>cmp</I
> to compare two files
	        within a script.</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;
   3&nbsp;ARGS=2  # Two args to script expected.
   4&nbsp;E_BADARGS=65
   5&nbsp;E_UNREADABLE=66
   6&nbsp;
   7&nbsp;if [ $# -ne "$ARGS" ]
   8&nbsp;then
   9&nbsp;  echo "Usage: `basename $0` file1 file2"
  10&nbsp;  exit $E_BADARGS
  11&nbsp;fi
  12&nbsp;
  13&nbsp;if [[ ! -r "$1" || ! -r "$2" ]]
  14&nbsp;then
  15&nbsp;  echo "Both files to be compared must exist and be readable."
  16&nbsp;  exit $E_UNREADABLE
  17&nbsp;fi
  18&nbsp;
  19&nbsp;cmp $1 $2 &#38;&#62; /dev/null  # /dev/null buries the output of the "cmp" command.
  20&nbsp;#   cmp -s $1 $2  has same result ("-s" silent flag to "cmp")
  21&nbsp;#   Thank you  Anders Gustavsson for pointing this out.
  22&nbsp;#
  23&nbsp;# Also works with 'diff', i.e.,   diff $1 $2 &#38;&#62; /dev/null
  24&nbsp;
  25&nbsp;if [ $? -eq 0 ]         # Test exit status of "cmp" command.
  26&nbsp;then
  27&nbsp;  echo "File \"$1\" is identical to file \"$2\"."
  28&nbsp;else  
  29&nbsp;  echo "File \"$1\" differs from file \"$2\"."
  30&nbsp;fi
  31&nbsp;
  32&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
>Use <B
CLASS="COMMAND"
>zcmp</B
> on
	      <I
CLASS="FIRSTTERM"
>gzipped</I
> files.</P
></TD
></TR
></TABLE
></DIV
></DD
><DT
><A
NAME="COMMREF"
></A
><B
CLASS="COMMAND"
>comm</B
></DT
><DD
><P
>Versatile file comparison utility. The files must be
	      sorted for this to be useful.</P
><P
><B
CLASS="COMMAND"
>comm
		<TT
CLASS="REPLACEABLE"
><I
>-options</I
></TT
>
		<TT
CLASS="REPLACEABLE"
><I
>first-file</I
></TT
>
		<TT
CLASS="REPLACEABLE"
><I
>second-file</I
></TT
></B
></P
><P
><TT
CLASS="USERINPUT"
><B
>comm file-1 file-2</B
></TT
> outputs three columns:
	      <UL
><LI
><P
>column 1 = lines unique to <TT
CLASS="FILENAME"
>file-1</TT
></P
></LI
><LI
><P
>column 2 = lines unique to <TT
CLASS="FILENAME"
>file-2</TT
></P
></LI
><LI
><P
>column 3 = lines common to both.</P
></LI
></UL
></P
><P
>The options allow suppressing output of one or more columns.
	      <UL
><LI
><P
><TT
CLASS="OPTION"
>-1</TT
> suppresses column
		    <TT
CLASS="LITERAL"
>1</TT
></P
></LI
><LI
><P
><TT
CLASS="OPTION"
>-2</TT
> suppresses column
		    <TT
CLASS="LITERAL"
>2</TT
></P
></LI
><LI
><P
><TT
CLASS="OPTION"
>-3</TT
> suppresses column
		    <TT
CLASS="LITERAL"
>3</TT
></P
></LI
><LI
><P
><TT
CLASS="OPTION"
>-12</TT
> suppresses both columns
		    <TT
CLASS="LITERAL"
>1</TT
> and <TT
CLASS="LITERAL"
>2</TT
>, etc.</P
></LI
></UL
>
	    </P
><P
>This command is useful for comparing
	      <SPAN
CLASS="QUOTE"
>"dictionaries"</SPAN
> or <I
CLASS="FIRSTTERM"
>word
	      lists</I
> -- sorted text files with one word per
	      line.</P
></DD
></DL
></DIV
><DIV
CLASS="VARIABLELIST"
><P
><B
><A
NAME="FAUTILS1"
></A
>Utilities</B
></P
><DL
><DT
><A
NAME="BASENAMEREF"
></A
><B
CLASS="COMMAND"
>basename</B
></DT
><DD
><P
>Strips the path information from a file name, printing
	      only the file name. The construction  <TT
CLASS="USERINPUT"
><B
>basename
		$0</B
></TT
> lets the script know its name, that is, the name it
	      was invoked by. This can be used for <SPAN
CLASS="QUOTE"
>"usage"</SPAN
> messages if, 
	      for example a script is called with missing arguments:
              <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;echo "Usage: `basename $0` arg1 arg2 ... argn"</PRE
></TD
></TR
></TABLE
>
	    </P
></DD
><DT
><A
NAME="DIRNAMEREF"
></A
><B
CLASS="COMMAND"
>dirname</B
></DT
><DD
><P
>Strips the <B
CLASS="COMMAND"
>basename</B
> from
	    a filename, printing only the path information.</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
><B
CLASS="COMMAND"
>basename</B
> and <B
CLASS="COMMAND"
>dirname</B
>
		can operate on any arbitrary string. The argument
		does not need to refer to an existing file, or
		even be a filename for that matter (see <A
HREF="contributed-scripts.html#DAYSBETWEEN"
>Example A-7</A
>).</P
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="EX35"
></A
><P
><B
>Example 15-35. <I
CLASS="FIRSTTERM"
>basename</I
> and
	      <I
CLASS="FIRSTTERM"
>dirname</I
></B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;
   3&nbsp;a=/home/bozo/daily-journal.txt
   4&nbsp;
   5&nbsp;echo "Basename of /home/bozo/daily-journal.txt = `basename $a`"
   6&nbsp;echo "Dirname of /home/bozo/daily-journal.txt = `dirname $a`"
   7&nbsp;echo
   8&nbsp;echo "My own home is `basename ~/`."         # `basename ~` also works.
   9&nbsp;echo "The home of my home is `dirname ~/`."  # `dirname ~`  also works.
  10&nbsp;
  11&nbsp;exit 0</PRE
></TD
></TR
></TABLE
><HR></DIV
></DD
><DT
><A
NAME="SPLITREF"
></A
><B
CLASS="COMMAND"
>split</B
>, <A
NAME="CSPLITREF"
></A
><B
CLASS="COMMAND"
>csplit</B
></DT
><DD
><P
>These are utilities for splitting a file into smaller
	      chunks. Their usual use is for splitting up large files
	      in order to back them up on floppies or preparatory to
	      e-mailing or uploading them.</P
><P
>The <B
CLASS="COMMAND"
>csplit</B
> command splits a file
	      according to <I
CLASS="FIRSTTERM"
>context</I
>, the split occuring
	      where patterns are matched.</P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="SPLITCOPY"
></A
><P
><B
>Example 15-36. A script that copies itself in sections</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# splitcopy.sh
   3&nbsp;
   4&nbsp;#  A script that splits itself into chunks,
   5&nbsp;#+ then reassembles the chunks into an exact copy
   6&nbsp;#+ of the original script.
   7&nbsp;
   8&nbsp;CHUNKSIZE=4    #  Size of first chunk of split files.
   9&nbsp;OUTPREFIX=xx   #  csplit prefixes, by default,
  10&nbsp;               #+ files with "xx" ...
  11&nbsp;
  12&nbsp;csplit "$0" "$CHUNKSIZE"
  13&nbsp;
  14&nbsp;# Some comment lines for padding . . .
  15&nbsp;# Line 15
  16&nbsp;# Line 16
  17&nbsp;# Line 17
  18&nbsp;# Line 18
  19&nbsp;# Line 19
  20&nbsp;# Line 20
  21&nbsp;
  22&nbsp;cat "$OUTPREFIX"* &#62; "$0.copy"  # Concatenate the chunks.
  23&nbsp;rm "$OUTPREFIX"*               # Get rid of the chunks.
  24&nbsp;
  25&nbsp;exit $?</PRE
></TD
></TR
></TABLE
><HR></DIV
></DD
></DL
></DIV
><DIV
CLASS="VARIABLELIST"
><P
><B
><A
NAME="FAENCENCR1"
></A
>Encoding and Encryption</B
></P
><DL
><DT
><A
NAME="SUMREF"
></A
><B
CLASS="COMMAND"
>sum</B
>, <A
NAME="CKSUMREF"
></A
><B
CLASS="COMMAND"
>cksum</B
>, <A
NAME="MD5SUMREF"
></A
><B
CLASS="COMMAND"
>md5sum</B
>, <A
NAME="SHA1SUMREF"
></A
><B
CLASS="COMMAND"
>sha1sum</B
></DT
><DD
><P
>These are utilities for generating checksums. A
	      <I
CLASS="FIRSTTERM"
>checksum</I
> is a number mathematically
	      calculated from the contents of a file, for the purpose
	      of checking its integrity. A script might refer to a list
	      of checksums for security purposes, such as ensuring
	      that the contents of key system files have not been
	      altered or corrupted. For security applications, use the
	      <B
CLASS="COMMAND"
>md5sum</B
> (<B
CLASS="COMMAND"
>m</B
>essage
	      <B
CLASS="COMMAND"
>d</B
>igest <B
CLASS="COMMAND"
>5</B
>
	      check<B
CLASS="COMMAND"
>sum</B
>) command, or better yet,
	      the newer <B
CLASS="COMMAND"
>sha1sum</B
> (Secure Hash
	      Algorithm).</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>cksum /boot/vmlinuz</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>1670054224 804083 /boot/vmlinuz</TT
>
 
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>echo -n "Top Secret" | cksum</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>3391003827 10</TT
>
 
 
 
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>md5sum /boot/vmlinuz</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>0f43eccea8f09e0a0b2b5cf1dcf333ba  /boot/vmlinuz</TT
>
 
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>echo -n "Top Secret" | md5sum</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>8babc97a6f62a4649716f4df8d61728f  -</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	  </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
>The <B
CLASS="COMMAND"
>cksum</B
> command shows the size,
	    in bytes, of its target, whether file or
	    <TT
CLASS="FILENAME"
>stdout</TT
>.</P
><P
>The <B
CLASS="COMMAND"
>md5sum</B
> and
	    <B
CLASS="COMMAND"
>sha1sum</B
> commands display a
	    <A
HREF="special-chars.html#DASHREF2"
>dash</A
> when they receive their input from
	    <TT
CLASS="FILENAME"
>stdout</TT
>.</P
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="FILEINTEGRITY"
></A
><P
><B
>Example 15-37. Checking file integrity</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# file-integrity.sh: Checking whether files in a given directory
   3&nbsp;#                    have been tampered with.
   4&nbsp;
   5&nbsp;E_DIR_NOMATCH=70
   6&nbsp;E_BAD_DBFILE=71
   7&nbsp;
   8&nbsp;dbfile=File_record.md5
   9&nbsp;# Filename for storing records (database file).
  10&nbsp;
  11&nbsp;
  12&nbsp;set_up_database ()
  13&nbsp;{
  14&nbsp;  echo ""$directory"" &#62; "$dbfile"
  15&nbsp;  # Write directory name to first line of file.
  16&nbsp;  md5sum "$directory"/* &#62;&#62; "$dbfile"
  17&nbsp;  # Append md5 checksums and filenames.
  18&nbsp;}
  19&nbsp;
  20&nbsp;check_database ()
  21&nbsp;{
  22&nbsp;  local n=0
  23&nbsp;  local filename
  24&nbsp;  local checksum
  25&nbsp;
  26&nbsp;  # ------------------------------------------- #
  27&nbsp;  #  This file check should be unnecessary,
  28&nbsp;  #+ but better safe than sorry.
  29&nbsp;
  30&nbsp;  if [ ! -r "$dbfile" ]
  31&nbsp;  then
  32&nbsp;    echo "Unable to read checksum database file!"
  33&nbsp;    exit $E_BAD_DBFILE
  34&nbsp;  fi
  35&nbsp;  # ------------------------------------------- #
  36&nbsp;
  37&nbsp;  while read record[n]
  38&nbsp;  do
  39&nbsp;
  40&nbsp;    directory_checked="${record[0]}"
  41&nbsp;    if [ "$directory_checked" != "$directory" ]
  42&nbsp;    then
  43&nbsp;      echo "Directories do not match up!"
  44&nbsp;      # Tried to use file for a different directory.
  45&nbsp;      exit $E_DIR_NOMATCH
  46&nbsp;    fi
  47&nbsp;
  48&nbsp;    if [ "$n" -gt 0 ]   # Not directory name.