communications.html

Shall高级编程

> of
	      <SPAN
CLASS="ERRORCODE"
>0</SPAN
>. This can be tested for in a
	      script.</P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;  HNAME=nastyspammer.com
   2&nbsp;# HNAME=$HOST     # Debug: test for localhost.
   3&nbsp;count=2  # Send only two pings.
   4&nbsp;
   5&nbsp;if [[ `ping -c $count "$HNAME"` ]]
   6&nbsp;then
   7&nbsp;  echo ""$HNAME" still up and broadcasting spam your way."
   8&nbsp;else
   9&nbsp;  echo ""$HNAME" seems to be down. Pity."
  10&nbsp;fi</PRE
></TD
></TR
></TABLE
></P
></DD
><DT
><A
NAME="WHOISREF"
></A
><B
CLASS="COMMAND"
>whois</B
></DT
><DD
><P
>Perform a DNS (Domain Name System) lookup.
	      The <TT
CLASS="OPTION"
>-h</TT
> option permits specifying which
	      particular <I
CLASS="FIRSTTERM"
>whois</I
> server to query. See
	      <A
HREF="othertypesv.html#EX18"
>Example 4-6</A
> and <A
HREF="communications.html#SPAMLOOKUP"
>Example 15-39</A
>.</P
></DD
><DT
><A
NAME="FINGERREF"
></A
><B
CLASS="COMMAND"
>finger</B
></DT
><DD
><P
>Retrieve information about users on a
	      network. Optionally, this command can display
	      a user's <TT
CLASS="FILENAME"
>~/.plan</TT
>,
	      <TT
CLASS="FILENAME"
>~/.project</TT
>, and
	      <TT
CLASS="FILENAME"
>~/.forward</TT
> files, if present.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>finger</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>Login  Name           Tty      Idle  Login Time   Office     Office Phone
 bozo   Bozo Bozeman   tty1        8  Jun 25 16:59
 bozo   Bozo Bozeman   ttyp0          Jun 25 16:59
 bozo   Bozo Bozeman   ttyp1          Jun 25 17:07</TT
>
 
 
 
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>finger bozo</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>Login: bozo                             Name: Bozo Bozeman
 Directory: /home/bozo                   Shell: /bin/bash
 Office: 2355 Clown St., 543-1234
 On since Fri Aug 31 20:13 (MST) on tty1    1 hour 38 minutes idle
 On since Fri Aug 31 20:13 (MST) on pts/0   12 seconds idle
 On since Fri Aug 31 20:13 (MST) on pts/1
 On since Fri Aug 31 20:31 (MST) on pts/2   1 hour 16 minutes idle
 No mail.
 No Plan.</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	    </P
><P
>Out of security considerations, many networks disable
	      <B
CLASS="COMMAND"
>finger</B
> and its associated daemon.
	          <A
NAME="AEN12186"
HREF="#FTN.AEN12186"
>[1]</A
>
	      </P
></DD
><DT
><A
NAME="CHFNREF"
></A
><B
CLASS="COMMAND"
>chfn</B
></DT
><DD
><P
>Change information disclosed by the
	      <B
CLASS="COMMAND"
>finger</B
> command.</P
></DD
><DT
><A
NAME="VRFYREF"
></A
><B
CLASS="COMMAND"
>vrfy</B
></DT
><DD
><P
>Verify an Internet e-mail address.</P
><P
>This command seems to be missing from newer Linux
	      distros.</P
></DD
></DL
></DIV
><DIV
CLASS="VARIABLELIST"
><P
><B
><A
NAME="COMMREMOTE1"
></A
>Remote Host Access</B
></P
><DL
><DT
><A
NAME="RXREF"
></A
><B
CLASS="COMMAND"
>sx</B
>, <B
CLASS="COMMAND"
>rx</B
></DT
><DD
><P
>The <B
CLASS="COMMAND"
>sx</B
> and <B
CLASS="COMMAND"
>rx</B
>
	      command set serves to transfer files to and from a remote
	      host using the <I
CLASS="FIRSTTERM"
>xmodem</I
> protocol. These
	      are generally part of a communications package, such as
	      <B
CLASS="COMMAND"
>minicom</B
>.</P
></DD
><DT
><A
NAME="RZREF"
></A
><B
CLASS="COMMAND"
>sz</B
>, <B
CLASS="COMMAND"
>rz</B
></DT
><DD
><P
>The <B
CLASS="COMMAND"
>sz</B
> and <B
CLASS="COMMAND"
>rz</B
>
	      command set serves to transfer files to and from a remote
	      host using the <I
CLASS="FIRSTTERM"
>zmodem</I
> protocol.
	      <I
CLASS="FIRSTTERM"
>Zmodem</I
> has certain advantages over
	      <I
CLASS="FIRSTTERM"
>xmodem</I
>, such as faster transmission
	      rate and resumption of interrupted file transfers.
	      Like <B
CLASS="COMMAND"
>sx</B
> and <B
CLASS="COMMAND"
>rx</B
>,
	      these are generally part of a communications package.</P
></DD
><DT
><A
NAME="FTPREF"
></A
><B
CLASS="COMMAND"
>ftp</B
></DT
><DD
><P
>Utility and protocol for uploading / downloading
	      files to or from a remote host. An ftp session can be automated
	      in a script (see <A
HREF="here-docs.html#EX72"
>Example 18-6</A
>, <A
HREF="contributed-scripts.html#ENCRYPTEDPW"
>Example A-4</A
>, and <A
HREF="contributed-scripts.html#FTPGET"
>Example A-13</A
>).</P
></DD
><DT
><A
NAME="UUCPREF"
></A
><B
CLASS="COMMAND"
>uucp</B
>, <A
NAME="UUXREF"
></A
><B
CLASS="COMMAND"
>uux</B
>, <A
NAME="CUREF"
></A
><B
CLASS="COMMAND"
>cu</B
></DT
><DD
><P
><B
CLASS="COMMAND"
>uucp</B
>: <I
CLASS="FIRSTTERM"
>UNIX to UNIX
	      copy</I
>. This is a communications package for
	      transferring files between UNIX servers. A shell script
	      is an effective way to handle a <B
CLASS="COMMAND"
>uucp</B
>
	      command sequence.</P
><P
>Since the advent of the Internet and e-mail,
	      <B
CLASS="COMMAND"
>uucp</B
> seems to have faded into obscurity,
	      but it still exists and remains perfectly workable in
	      situations where an Internet connection is not available
	      or appropriate. The advantage of <B
CLASS="COMMAND"
>uucp</B
>
	      is that it is fault-tolerant, so even if there is a service
	      interruption the copy operation will resume where it left
	      off when the connection is restored.</P
><P
>---</P
><P
><B
CLASS="COMMAND"
>uux</B
>: <I
CLASS="FIRSTTERM"
>UNIX to UNIX
	      execute</I
>. Execute a command on a remote system.
	      This command is part of the <B
CLASS="COMMAND"
>uucp</B
>
	      package.</P
><P
>---</P
><P
><B
CLASS="COMMAND"
>cu</B
>: <B
CLASS="COMMAND"
>C</B
>all
	      <B
CLASS="COMMAND"
>U</B
>p a remote system and connect as a
	      simple terminal. It is a sort of dumbed-down version of
	      <A
HREF="communications.html#TELNETREF"
>telnet</A
>. This command is
	      part of the <B
CLASS="COMMAND"
>uucp</B
> package.</P
></DD
><DT
><A
NAME="TELNETREF"
></A
><B
CLASS="COMMAND"
>telnet</B
></DT
><DD
><P
>Utility and protocol for connecting to a remote host.</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
>The <I
CLASS="FIRSTTERM"
>telnet</I
> protocol
	    contains security holes and should therefore probably be
	    avoided. Its use within a shell script is
	    <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>not</I
></SPAN
> recommended.</P
></TD
></TR
></TABLE
></DIV
></DD
><DT
><A
NAME="WGETREF"
></A
><B
CLASS="COMMAND"
>wget</B
></DT
><DD
><P
>The <B
CLASS="COMMAND"
>wget</B
> utility
	      <I
CLASS="FIRSTTERM"
>noninteractively</I
> retrieves or
	      downloads files from a Web or ftp site. It works well in a
	      script.</P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;wget -p http://www.xyz23.com/file01.html
   2&nbsp;#  The -p or --page-requisite option causes wget to fetch all files
   3&nbsp;#+ required to display the specified page.
   4&nbsp;
   5&nbsp;wget -r ftp://ftp.xyz24.net/~bozo/project_files/ -O $SAVEFILE
   6&nbsp;#  The -r option recursively follows and retrieves all links
   7&nbsp;#+ on the specified site.
   8&nbsp;
   9&nbsp;wget -c ftp://ftp.xyz25.net/bozofiles/filename.tar.bz2
  10&nbsp;#  The -c option lets wget resume an interrupted download.
  11&nbsp;#  This works with ftp servers and many HTTP sites.</PRE
></TD
></TR
></TABLE
></P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="QUOTEFETCH"
></A
><P
><B
>Example 15-41. Getting a stock quote</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# quote-fetch.sh: Download a stock quote.
   3&nbsp;
   4&nbsp;
   5&nbsp;E_NOPARAMS=66
   6&nbsp;
   7&nbsp;if [ -z "$1" ]  # Must specify a stock (symbol) to fetch.
   8&nbsp;  then echo "Usage: `basename $0` stock-symbol"
   9&nbsp;  exit $E_NOPARAMS
  10&nbsp;fi
  11&nbsp;
  12&nbsp;stock_symbol=$1
  13&nbsp;
  14&nbsp;file_suffix=.html
  15&nbsp;# Fetches an HTML file, so name it appropriately.
  16&nbsp;URL='http://finance.yahoo.com/q?s='
  17&nbsp;# Yahoo finance board, with stock query suffix.
  18&nbsp;
  19&nbsp;# -----------------------------------------------------------
  20&nbsp;wget -O ${stock_symbol}${file_suffix} "${URL}${stock_symbol}"
  21&nbsp;# -----------------------------------------------------------
  22&nbsp;
  23&nbsp;
  24&nbsp;# To look up stuff on http://search.yahoo.com:
  25&nbsp;# -----------------------------------------------------------
  26&nbsp;# URL="http://search.yahoo.com/search?fr=ush-news&#38;p=${query}"
  27&nbsp;# wget -O "$savefilename" "${URL}"
  28&nbsp;# -----------------------------------------------------------
  29&nbsp;# Saves a list of relevant URLs.
  30&nbsp;
  31&nbsp;exit $?
  32&nbsp;
  33&nbsp;# Exercises:
  34&nbsp;# ---------
  35&nbsp;#
  36&nbsp;# 1) Add a test to ensure the user running the script is on-line.
  37&nbsp;#    (Hint: parse the output of 'ps -ax' for "ppp" or "connect."
  38&nbsp;#
  39&nbsp;# 2) Modify this script to fetch the local weather report,
  40&nbsp;#+   taking the user's zip code as an argument.</PRE
></TD
></TR
></TABLE
><HR></DIV
><P
>See also <A
HREF="contributed-scripts.html#WGETTER2"
>Example A-32</A
> and <A
HREF="contributed-scripts.html#BASHPODDER"
>Example A-33</A
>.</P
></DD
><DT
><A
NAME="LYNXREF"
></A
><B
CLASS="COMMAND"
>lynx</B
></DT
><DD
><P
>The <B
CLASS="COMMAND"
>lynx</B
> Web and file browser
	      can be used inside a script (with the
	      <TT
CLASS="OPTION"
>-dump</TT
> option) to retrieve a file from a Web or 
	      ftp site noninteractively.</P
><P
>	   <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;lynx -dump http://www.xyz23.com/file01.html &#62;$SAVEFILE</PRE
></TD
></TR
></TABLE
>
            </P
><P
>With the <TT
CLASS="OPTION"
>-traversal</TT
> option,
	      <B
CLASS="COMMAND"
>lynx</B
> starts at the HTTP URL specified
	      as an argument, then <SPAN
CLASS="QUOTE"
>"crawls"</SPAN
> through all
	      links located on that particular server. Used together
	      with the <TT
CLASS="OPTION"
>-crawl</TT
> option, outputs page text
	      to a log file.</P
></DD
><DT
><A
NAME="RLOGINREF"
></A
><B
CLASS="COMMAND"
>rlogin</B
></DT
><DD
><P
><TT
CLASS="REPLACEABLE"
><I
>Remote login</I
></TT
>, initates a
	      session on a remote host. This command has security issues,
	      so use <A
HREF="communications.html#SSHREF"
>ssh</A
> instead.</P
></DD
><DT
><A
NAME="RSHREF"
></A
><B
CLASS="COMMAND"
>rsh</B
></DT
><DD
><P
><TT
CLASS="REPLACEABLE"
><I
>Remote shell</I
></TT
>, executes
	      command(s) on a remote host. This has security issues,
	      so use <B
CLASS="COMMAND"
>ssh</B
> instead.</P
></DD
><DT
><A
NAME="RCPREF"
></A
><B
CLASS="COMMAND"
>rcp</B
></DT
><DD
><P
><TT
CLASS="REPLACEABLE"
><I
>Remote copy</I
></TT
>, copies files
	      between two different networked machines.</P
></DD
><DT
><A
NAME="RSYNCREF"
></A
><B
CLASS="COMMAND"
>rsync</B
></DT
><DD
><P
><TT
CLASS="REPLACEABLE"
><I
>Remote synchronize</I
></TT
>, updates
	    (synchronizes) files
	      between two different networked machines.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>rsync -a ~/sourcedir/*txt /node1/subdirectory/</B
></TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	    </P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="FC4UPD"
></A
><P
><B
>Example 15-42. Updating FC4</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# fc4upd.sh
   3&nbsp;
   4&nbsp;# Script author: Frank Wang.
   5&nbsp;# Slight stylistic modifications by ABS Guide author.
   6&nbsp;# Used in ABS Guide with permission.
   7&nbsp;
   8&nbsp;
   9&nbsp;#  Download Fedora Core 4 update from mirror site using rsync. 
  10&nbsp;#  Should also work for newer Fedora Cores -- 5, 6, . . .
  11&nbsp;#  Only download latest package if multiple versions exist,
  12&nbsp;#+ to save space.
  13&nbsp;
  14&nbsp;URL=rsync://distro.ibiblio.org/fedora-linux-core/updates/
  15&nbsp;# URL=rsync://ftp.kddilabs.jp/fedora/core/updates/
  16&nbsp;# URL=rsync://rsync.planetmirror.com/fedora-linux-core/updates/
  17&nbsp;
  18&nbsp;DEST=${1:-/var/www/html/fedora/updates/}
  19&nbsp;LOG=/tmp/repo-update-$(/bin/date +%Y-%m-%d).txt
  20&nbsp;PID_FILE=/var/run/${0##*/}.pid
  21&nbsp;
  22&nbsp;E_RETURN=65        # Something unexpected happened.
  23&nbsp;
  24&nbsp;
  25&nbsp;# General rsync options
  26&nbsp;# -r: recursive download