filearchiv.html

Shall高级编程

>"command"</SPAN
> in the
	      <TT
CLASS="REPLACEABLE"
><I
>whatis</I
></TT
> database. This is useful
	      for identifying system commands and important configuration
	      files. Consider it a simplified <B
CLASS="COMMAND"
>man</B
>
	      command.</P
><P
><TT
CLASS="USERINPUT"
><B
>$bash whatis whatis</B
></TT
>
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="COMPUTEROUTPUT"
>whatis               (1)  - search the whatis database for complete words</TT
></PRE
></TD
></TR
></TABLE
>
	  </P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="WHAT"
></A
><P
><B
>Example 15-32. Exploring <TT
CLASS="FILENAME"
>/usr/X11R6/bin</TT
></B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;
   3&nbsp;# What are all those mysterious binaries in /usr/X11R6/bin?
   4&nbsp;
   5&nbsp;DIRECTORY="/usr/X11R6/bin"
   6&nbsp;# Try also "/bin", "/usr/bin", "/usr/local/bin", etc.
   7&nbsp;
   8&nbsp;for file in $DIRECTORY/*
   9&nbsp;do
  10&nbsp;  whatis `basename $file`   # Echoes info about the binary.
  11&nbsp;done
  12&nbsp;
  13&nbsp;exit 0
  14&nbsp;
  15&nbsp;# You may wish to redirect output of this script, like so:
  16&nbsp;# ./what.sh &#62;&#62;whatis.db
  17&nbsp;# or view it a page at a time on stdout,
  18&nbsp;# ./what.sh | less</PRE
></TD
></TR
></TABLE
><HR></DIV
><P
>See also <A
HREF="loops.html#FILEINFO"
>Example 10-3</A
>.</P
></DD
><DT
><A
NAME="VDIRREF"
></A
><B
CLASS="COMMAND"
>vdir</B
></DT
><DD
><P
>Show a detailed directory listing. The effect is similar to
	      <A
HREF="external.html#LSREF"
>ls -lb</A
>.</P
><P
>This is one of the GNU
	    <I
CLASS="FIRSTTERM"
>fileutils</I
>.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>vdir</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>total 10
 -rw-r--r--    1 bozo  bozo      4034 Jul 18 22:04 data1.xrolo
 -rw-r--r--    1 bozo  bozo      4602 May 25 13:58 data1.xrolo.bak
 -rw-r--r--    1 bozo  bozo       877 Dec 17  2000 employment.xrolo</TT
>
 
 <TT
CLASS="PROMPT"
>bash </TT
><TT
CLASS="USERINPUT"
><B
>ls -l</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>total 10
 -rw-r--r--    1 bozo  bozo      4034 Jul 18 22:04 data1.xrolo
 -rw-r--r--    1 bozo  bozo      4602 May 25 13:58 data1.xrolo.bak
 -rw-r--r--    1 bozo  bozo       877 Dec 17  2000 employment.xrolo</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	      </P
></DD
><DT
><A
NAME="LOCATEREF"
></A
><B
CLASS="COMMAND"
>locate</B
>, <A
NAME="SLOCATEREF"
></A
><B
CLASS="COMMAND"
>slocate</B
></DT
><DD
><P
>The <B
CLASS="COMMAND"
>locate</B
> command searches for files using a
	      database stored for just that purpose. The
	      <B
CLASS="COMMAND"
>slocate</B
> command is the secure version of
	      <B
CLASS="COMMAND"
>locate</B
> (which may be aliased to
	      <B
CLASS="COMMAND"
>slocate</B
>).</P
><P
><TT
CLASS="USERINPUT"
><B
>$bash locate hickson</B
></TT
>
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="COMPUTEROUTPUT"
>/usr/lib/xephem/catalogs/hickson.edb</TT
></PRE
></TD
></TR
></TABLE
></P
></DD
><DT
><A
NAME="READLINKREF"
></A
><B
CLASS="COMMAND"
>readlink</B
></DT
><DD
><P
>Disclose the file that a symbolic link points to.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>readlink /usr/bin/awk</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>../../bin/gawk</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	    </P
></DD
><DT
><A
NAME="STRINGSREF"
></A
><B
CLASS="COMMAND"
>strings</B
></DT
><DD
><P
>Use the <B
CLASS="COMMAND"
>strings</B
> command to find
	      printable strings in a binary or data file. It will list
	      sequences of printable characters found in the target
	      file. This might be handy for a quick 'n dirty examination
	      of a core dump or for looking at an unknown graphic image
	      file (<TT
CLASS="USERINPUT"
><B
>strings image-file | more</B
></TT
> might
	      show something like <I
CLASS="FIRSTTERM"
>JFIF</I
>,
	      which would identify the file as a <I
CLASS="FIRSTTERM"
>jpeg</I
>
	      graphic). In a script, you would probably
	      parse the output of <B
CLASS="COMMAND"
>strings</B
>
	      with <A
HREF="textproc.html#GREPREF"
>grep</A
> or <A
HREF="sedawk.html#SEDREF"
>sed</A
>. See <A
HREF="loops.html#BINGREP"
>Example 10-7</A
>
	      and <A
HREF="loops.html#FINDSTRING"
>Example 10-9</A
>.</P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="WSTRINGS"
></A
><P
><B
>Example 15-33. An <SPAN
CLASS="QUOTE"
>"improved"</SPAN
>
	      <I
CLASS="FIRSTTERM"
>strings</I
> command</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# wstrings.sh: "word-strings" (enhanced "strings" command)
   3&nbsp;#
   4&nbsp;#  This script filters the output of "strings" by checking it
   5&nbsp;#+ against a standard word list file.
   6&nbsp;#  This effectively eliminates gibberish and noise,
   7&nbsp;#+ and outputs only recognized words.
   8&nbsp;
   9&nbsp;# ===========================================================
  10&nbsp;#                 Standard Check for Script Argument(s)
  11&nbsp;ARGS=1
  12&nbsp;E_BADARGS=65
  13&nbsp;E_NOFILE=66
  14&nbsp;
  15&nbsp;if [ $# -ne $ARGS ]
  16&nbsp;then
  17&nbsp;  echo "Usage: `basename $0` filename"
  18&nbsp;  exit $E_BADARGS
  19&nbsp;fi
  20&nbsp;
  21&nbsp;if [ ! -f "$1" ]                      # Check if file exists.
  22&nbsp;then
  23&nbsp;    echo "File \"$1\" does not exist."
  24&nbsp;    exit $E_NOFILE
  25&nbsp;fi
  26&nbsp;# ===========================================================
  27&nbsp;
  28&nbsp;
  29&nbsp;MINSTRLEN=3                           #  Minimum string length.
  30&nbsp;WORDFILE=/usr/share/dict/linux.words  #  Dictionary file.
  31&nbsp;                                      #  May specify a different
  32&nbsp;                                      #+ word list file
  33&nbsp;                                      #+ of one-word-per-line format.
  34&nbsp;
  35&nbsp;
  36&nbsp;wlist=`strings "$1" | tr A-Z a-z | tr '[:space:]' Z | \
  37&nbsp;tr -cs '[:alpha:]' Z | tr -s '\173-\377' Z | tr Z ' '`
  38&nbsp;
  39&nbsp;# Translate output of 'strings' command with multiple passes of 'tr'.
  40&nbsp;#  "tr A-Z a-z"  converts to lowercase.
  41&nbsp;#  "tr '[:space:]'"  converts whitespace characters to Z's.
  42&nbsp;#  "tr -cs '[:alpha:]' Z"  converts non-alphabetic characters to Z's,
  43&nbsp;#+ and squeezes multiple consecutive Z's.
  44&nbsp;#  "tr -s '\173-\377' Z"  converts all characters past 'z' to Z's
  45&nbsp;#+ and squeezes multiple consecutive Z's,
  46&nbsp;#+ which gets rid of all the weird characters that the previous
  47&nbsp;#+ translation failed to deal with.
  48&nbsp;#  Finally, "tr Z ' '" converts all those Z's to whitespace,
  49&nbsp;#+ which will be seen as word separators in the loop below.
  50&nbsp;
  51&nbsp;#  ****************************************************************
  52&nbsp;#  Note the technique of feeding the output of 'tr' back to itself,
  53&nbsp;#+ but with different arguments and/or options on each pass.
  54&nbsp;#  ****************************************************************
  55&nbsp;
  56&nbsp;
  57&nbsp;for word in $wlist                    # Important:
  58&nbsp;                                      # $wlist must not be quoted here.
  59&nbsp;                                      # "$wlist" does not work.
  60&nbsp;                                      # Why not?
  61&nbsp;do
  62&nbsp;
  63&nbsp;  strlen=${#word}                     # String length.
  64&nbsp;  if [ "$strlen" -lt "$MINSTRLEN" ]   # Skip over short strings.
  65&nbsp;  then
  66&nbsp;    continue
  67&nbsp;  fi
  68&nbsp;
  69&nbsp;  grep -Fw $word "$WORDFILE"          #  Match whole words only.
  70&nbsp;#      ^^^                            #  "Fixed strings" and
  71&nbsp;                                      #+ "whole words" options. 
  72&nbsp;
  73&nbsp;done  
  74&nbsp;
  75&nbsp;
  76&nbsp;exit $?</PRE
></TD
></TR
></TABLE
><HR></DIV
></DD
></DL
></DIV
><DIV
CLASS="VARIABLELIST"
><P
><B
><A
NAME="COMPARISONN1"
></A
>Comparison</B
></P
><DL
><DT
><A
NAME="DIFFREF"
></A
><B
CLASS="COMMAND"
>diff</B
>, <B
CLASS="COMMAND"
>patch</B
></DT
><DD
><P
><B
CLASS="COMMAND"
>diff</B
>: flexible file comparison
	      utility. It compares the target files line-by-line
	      sequentially.  In some applications, such as comparing
	      word dictionaries, it may be helpful to filter the
	      files through <A
HREF="textproc.html#SORTREF"
>sort</A
>
	      and <B
CLASS="COMMAND"
>uniq</B
> before piping them
	      to <B
CLASS="COMMAND"
>diff</B
>. <TT
CLASS="USERINPUT"
><B
>diff file-1
	      file-2</B
></TT
> outputs the lines in the files that
	      differ, with carets showing which file each particular
	      line belongs to.</P
><P
>The <TT
CLASS="OPTION"
>--side-by-side</TT
> option to
	    <B
CLASS="COMMAND"
>diff</B
> outputs each compared file, line by
	    line, in separate columns, with non-matching lines marked. The
	    <TT
CLASS="OPTION"
>-c</TT
> and <TT
CLASS="OPTION"
>-u</TT
> options likewise
	    make the output of the command easier to interpret.</P
><P
>There are available various fancy frontends for
	    <B
CLASS="COMMAND"
>diff</B
>, such as <B
CLASS="COMMAND"
>sdiff</B
>,
	    <B
CLASS="COMMAND"
>wdiff</B
>, <B
CLASS="COMMAND"
>xdiff</B
>, and
	    <B
CLASS="COMMAND"
>mgdiff</B
>. </P
><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 <B
CLASS="COMMAND"
>diff</B
> command returns an exit
	    status of 0 if the compared files are identical, and 1 if
	    they differ. This permits use of <B
CLASS="COMMAND"
>diff</B
>
	    in a test construct within a shell script (see
	    below).</P
></TD
></TR
></TABLE
></DIV
><P
>A common use for <B
CLASS="COMMAND"
>diff</B
> is generating
	      difference files to be used with <B
CLASS="COMMAND"
>patch</B
>
	      The <TT
CLASS="OPTION"
>-e</TT
> option outputs files suitable
	      for <B
CLASS="COMMAND"
>ed</B
> or <B
CLASS="COMMAND"
>ex</B
>
	      scripts.</P
><P
><A
NAME="PATCHREF"
></A
></P
><P
><B
CLASS="COMMAND"
>patch</B
>: flexible versioning
	      utility. Given a difference file generated by
	      <B
CLASS="COMMAND"
>diff</B
>, <B
CLASS="COMMAND"
>patch</B
> can
	      upgrade a previous version of a package to a newer version.
	      It is much more convenient to distribute a relatively
	      small <SPAN
CLASS="QUOTE"
>"diff"</SPAN
> file than the entire body of a
	      newly revised package. Kernel <SPAN
CLASS="QUOTE"
>"patches"</SPAN
> have
	      become the preferred method of distributing the frequent
	      releases of the Linux kernel.</P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;patch -p1 &#60;patch-file
   2&nbsp;# Takes all the changes listed in 'patch-file'
   3&nbsp;# and applies them to the files referenced therein.
   4&nbsp;# This upgrades to a newer version of the package.</PRE
></TD
></TR
></TABLE
></P
><P
>Patching the kernel:</P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;cd /usr/src
   2&nbsp;gzip -cd patchXX.gz | patch -p0
   3&nbsp;# Upgrading kernel source using 'patch'.
   4&nbsp;# From the Linux kernel docs "README",
   5&nbsp;# by anonymous author (Alan Cox?).</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"
>diff</B
> command can also
	      recursively compare directories (for the filenames
	      present).</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>diff -r ~/notes1 ~/notes2</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>Only in /home/bozo/notes1: file02
 Only in /home/bozo/notes1: file03
 Only in /home/bozo/notes2: file04</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	    </P
></TD
></TR
></TABLE
></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
><A
NAME="ZDIFFREF"
></A
></P
><P
>Use <B
CLASS="COMMAND"
>zdiff</B
> to compare
	       <I
CLASS="FIRSTTERM"
>gzipped</I
> files.</P
></TD
></TR
></TABLE
></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
><A
NAME="DIFFSTATREF"
></A
></P
><P
>Use <B
CLASS="COMMAND"
>diffstat</B
> to create
	       a histogram (point-distribution graph) of output from
	       <B
CLASS="COMMAND"
>diff</B
>.</P
></TD
></TR
></TABLE
></DIV
></DD
><DT
><A
NAME="DIFF3REF"
></A
><B
CLASS="COMMAND"
>diff3</B
></DT
><DD
><P
>An extended version of <B
CLASS="COMMAND"
>diff</B
> that compares
	      three files at a time. This command returns an exit value
	      of 0 upon successful execution, but unfortunately this gives
	      no information about the results of the comparison.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>diff3 file-1 file-2 file-3</B