2002-02-18 00:00:00 +00:00
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<!DOCTYPE html PUBLIC "-//W3C/DTD HTML 3.2 Final//EN">
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2001-01-15 00:00:00 +00:00
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<html><head>
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<title>BVI: Partial File Read</title>
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<link rel=stylesheet type="text/css" href="bvi.css">
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</head><body bgcolor="#ffffff" background="gif/bg2.gif">
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<a name="top"></a>
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<table width="100%" border="0" cellspacing="0" cellpadding="0">
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<tr><td width="1%" valign="top" align="center">
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2002-02-18 00:00:00 +00:00
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<img src="gif/dot.gif" width="130" height="1" alt="">
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2001-01-15 00:00:00 +00:00
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<hr noshade width="60%">
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<p>
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<a class="thl" href="index.html">Home</a><br>
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</p>
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<p>
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<a class="thl" href="quick.html">Quick Tutorial</a><br>
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<a class="ths" href="qt_edit.html">Editing Files</a><br>
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<a class="ths" href="qt_search.html">Search Commands</a><br>
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<a class="ths" href="qt_bit.html">Bit-wise Operations</a><br>
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<a class="ths" href="qt_find.html">Find and Replace</a><br>
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<a class="ths" href="qt_yank.html">Yank and Put</a><br>
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<a class="ths" href="qt_set.html">Settings</a><br>
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<font color="#ffffff" class="ths">Partial File Read<br></font>
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</p>
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<p>
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<a class="thl" href="download.html">Download</a><br>
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</p>
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<p>
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<a class="thl" href="install.html">Installation</a><br>
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</p>
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<p>
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<a class="thl" href="overview.html">Command Overview</a><br>
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</p>
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<p>
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<a class="thl" href="bmore.html">bmore</a><br>
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</p>
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<p>
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<a class="thl" href="german.html">Deutsche Beschreibung</a><br>
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</p>
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<hr noshade width="60%">
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</td>
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2002-02-18 00:00:00 +00:00
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<td width="1%"><img src="gif/dot.gif" width="40" height="1" alt=""></td>
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2001-01-15 00:00:00 +00:00
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<td width="99%">
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<table width="100%" cellspacing="0" cellpadding="0" border="0">
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<tr><td width="99%">
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<font class="head">Quick Tutorial</font>
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<br><font class="sub">Partial File Read</font>
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</td>
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<td align="right" valign="bottom" width="116" rowspan="2">
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<a href="index.html">
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<img src="gif/bvi_s.gif" alt="BVI" width="116"
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height="62" border="0"></a>
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</td></tr>
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<tr><td valign="bottom">
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<hr noshade>
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</td></tr></table>
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<p>
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A new feature of version 1.3.0 is the Partial File Read.
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If you want to edit a file, you have not to read the file into
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memory but only the part you want to edit. You can write back this part
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into the file after editing.
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<BR>
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Example:
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<BR>
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You have to change only some bytes of the header of a graphic file
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(e.g. a color). Graphic files can be very large. With the <TT>-s</TT>
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option you can load only the first kilobyte of the file:
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<PRE>
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bvi -s 1000 large.gif
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</PRE>
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In this case of course you cannot insert or delete bytes of the file.
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The editor is set to the <I>no memmove</I> mode. You can write back
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only as much bytes as you read before. If you add or delete bytes
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even though, the extra bytes will be ignored or garbage will be
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written to the file.
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<P>
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It is also possible to start not at the begin of the file, but at a
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certain address. To do this you have to use the option <TT>-b</TT>.
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You can read the file from this starting point until the end of the file
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or you can use the <TT>-s</TT> option to specify a size or the
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<TT>-e</TT> option to specify an end address.
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<P>
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If you read the file not from the start an offset will be set to
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display the correct address at the left side of the screen. If you change this
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offset with the <TT>:set offset=<I>nnnn</I></TT> command, this has
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<B>no</B> effect to the write back operation. The edited part of the
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file will always be written back at the same position, where it was read.
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<P>
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In the Linux <TT>/proc</TT> directory there are files which are listed
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with length 0 in a directory listing. But in reality they have a content.
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You can read this files, if you use the <TT>-s</TT> option and guess a
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size. This size should be a little bit larger than the size you expect.
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<P>
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The same guidlines can be used, if you load a block device, e.g. a
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floppy disk.
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<PRE>
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bvi -s 1450k /dev/fd0
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</PRE>
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After reading the device, you get a message with the value of the
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real read bytes at the bottom of the screen:
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<PRE>
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"/dev/fd0" range 0-1474559
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</PRE>
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Note that the <I>size</I> value will be used to allocate memory before
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reading the file. Therefore do not choose a too large size.<BR>
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Note further, that <I>1450k</I> in the example above is calculated as
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<I>1450 * 1024</I> bytes. This gives <I>1484800</I> bytes allocated size.
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If <STRONG>bvi</STRONG> reads the exact number of bytes you have asked for
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in the <TT>-s</TT> option, the file may be larger.
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<P>
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<B>WARNING:</B>
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<BLOCKQUOTE>
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Do not use <STRONG>bvi</STRONG> at mounted disk devices!<BR>
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Do not edit disk devices, if you don't know exactly what you change!<BR>
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You may make your disk unreadable by editing it!!
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</BLOCKQUOTE>
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<H3>Interaction with <STRONG>bmore</STRONG></H3>
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You may use <STRONG>bmore</STRONG> to browse through large files or
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devices. You may use the ASCII - or Hex - search possibilities to
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locate a certain section of the file.<BR>
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If you see the desired part of the file on your screen, press <I><B>w</B></I> to
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read the contents of the file displayed currently on your screen into
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<STRONG>bvi</STRONG>. You can use a decimal prefix at the <I><B>w</B></I> -
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command to read more or less bytes than displayed into <STRONG>bvi</STRONG>.
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<BR>
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The letter <I><B>w</B></I> is the next letter after <I><B>v</B></I>, which
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is used in more and bmore to read the whole file into vi or bvi!
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<P>
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If you used the <TT>ZZ</TT> or <TT>:w</TT> command, this part of the file will be
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written back into the original file.
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<p><font size="-1">
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<a class="btop" href="#top">
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<img border="0" width="16" height="7" src="gif/up.gif"
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alt="Back to the top">Back to the top</a>
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</font>
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<hr noshade>
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<i>Last update: Sun Jul 09 21:57:38 CEST 2000 by Gerhard Bürgmann</i>
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</td></tr></table>
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</body></html>
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