blocks|key|1504627|text|您是否尝试过使用netcat+(nc)而不是telnet？它具有更大的灵活性，包括能够设置超时：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1504628|echo+'QUIT'+%7C+nc+-w+SECONDS+YOUR_HOST+PORT
#+e.g.
echo+"QUIT"+%7C+nc+-w+5+++++++localhost+21|code-block|syntax|javascript|1504629|-w+5选项将在5秒后使连接超时。|1504630|entityMap^0|G|2|0|0|0|4|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|N|$]]

Have you tried using netcat (<code>nc</code>) instead of telnet? It has more flexibility, including being able to set the timeout:

<pre><code>echo 'QUIT' | nc -w SECONDS YOUR_HOST PORT
# e.g.
echo "QUIT" | nc -w 5 localhost 21
</code></pre>

The <code>-w 5</code> option will timeout the connection after 5 seconds.

blocks|key|1504680|text|使用start+a+process休眠并终止telnet进程。大致如下：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1504681|echo+QUIT+>quit.txt
telnet+$i+21+<+quit.txt+&
sleep+10+&&+kill+-9+%251+&
ex=wait+%251
kill+%252
#+Now+check+$ex+for+exit+status+of+telnet.++Note:+127+inidicates+success+as+the
#+telnet+process+completed+before+we+got+to+the+wait.|code-block|syntax|javascript|1504682|当涉及到第一个作业的退出代码时，我避免了echo+QUIT+%7C+telnet管道，以便不会有任何歧义。|1504683|此代码尚未经过测试。|1504684|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Use start a process to sleep and kill the telnet process. Roughly:

<pre><code>echo QUIT &gt;quit.txt
telnet $i 21 &lt; quit.txt &amp;
sleep 10 &amp;&amp; kill -9 %1 &amp;
ex=wait %1
kill %2
# Now check $ex for exit status of telnet. Note: 127 inidicates success as the
# telnet process completed before we got to the wait.
</code></pre>

I avoided the echo QUIT | telnet pipeline to leave no ambiguity when it comes to the exit code of the first job.

This code has not been tested.

blocks|key|1504727|text|如果您有nmap|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1504728|+nmap+-iL+hostfile+-p21++%7C+awk+'/Interesting/{ip=$NF}/ftp/&&/open/{print+"ftp+port+opened+for:+"ip}'|code-block|syntax|javascript|1504729|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

if you have nmap

<pre><code> nmap -iL hostfile -p21 | awk '/Interesting/{ip=$NF}/ftp/&amp;&amp;/open/{print "ftp port opened for: "ip}'
</code></pre>

blocks|key|1504757|text|尝试使用timeout3脚本是非常健壮的，我在不同的情况下使用了很多，没有问题。该示例仅等待3秒，尝试检查ssh端口是否打开。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1504758|>+echo+QUIT+>+quit.txt
>+./timeout3+-t+3+telnet+HOST+22+<+quit.txt+|code-block|syntax|javascript|1504759|输出:您可以使用grep表示“已连接”或“已终止”|1504760|timeout3文件内容：|1504761|1504762|#!/bin/bash
#
#+The+Bash+shell+script+executes+a+command+with+a+time-out.
#+Upon+time-out+expiration+SIGTERM+(15)+is+sent+to+the+process.+If+the+signal
#+is+blocked,+then+the+subsequent+SIGKILL+(9)+terminates+it.
#
#+Based+on+the+Bash+documentation+example.
#+If+you+find+it+suitable,+feel+free+to+include
#+anywhere:+the+very+same+logic+as+in+the+original+examples/scripts,+a
#+little+more+transparent+implementation+to+my+taste.
#
#+Dmitry+V+Golovashkin+<Dmitry.Golovashkin@sas.com>

scriptName="${0##*/}"
declare+-i+DEFAULT_TIMEOUT=9
declare+-i+DEFAULT_INTERVAL=1
declare+-i+DEFAULT_DELAY=1
#+Timeout.
declare+-i+timeout=DEFAULT_TIMEOUT

#+Interval+between+checks+if+the+process+is+still+alive.
declare+-i+interval=DEFAULT_INTERVAL

#+Delay+between+posting+the+SIGTERM+signal+and+destroying+the+process+by+SIGKILL.
declare+-i+delay=DEFAULT_DELAY

function+printUsage()+{
++++cat+<<EOF

Synopsis
++++$scriptName+[-t+timeout]+[-i+interval]+[-d+delay]+command
++++Execute+a+command+with+a+time-out.
++++Upon+time-out+expiration+SIGTERM+(15)+is+sent+to+the+process.+If+SIGTERM
++++signal+is+blocked,+then+the+subsequent+SIGKILL+(9)+terminates+it.

++++-t+timeout
++++++++Number+of+seconds+to+wait+for+command+completion.
++++++++Default+value:+$DEFAULT_TIMEOUT+seconds.

++++-i+interval
++++++++Interval+between+checks+if+the+process+is+still+alive.
++++++++Positive+integer,+default+value:+$DEFAULT_INTERVAL+seconds.

++++-d+delay
++++++++Delay+between+posting+the+SIGTERM+signal+and+destroying+the
++++++++process+by+SIGKILL.+Default+value:+$DEFAULT_DELAY+seconds.

As+of+today,+Bash+does+not+support+floating+point+arithmetic+(sleep+does),
therefore+all+delay/time+values+must+be+integers.
EOF
}

#+Options.
while+getopts+":t:i:d:"+option;+do++
++++case+"$option"+in
++++++++t)+timeout=$OPTARG+;;
++++++++i)+interval=$OPTARG+;;
++++++++d)+delay=$OPTARG+;;
++++++++*)+printUsage;+exit+1+;;
++++esac
done
shift+$((OPTIND+-+1))

#+$#+should+be+at+least+1+(the+command+to+execute),+however+it+may+be+strictly
#+greater+than+1+if+the+command+itself+has+options.

if+(($#+==+0+%7C%7C+interval+<=+0));+then+
++++printUsage
++++exit+1
fi

#+kill+-0+pid+++Exit+code+indicates+if+a+signal+may+be+sent+to+$pid+process.
(
++++((t+=+timeout))

++++while+((t+>+0));+do
++++++++sleep+$interval
++++++++kill+-0+$$+%7C%7C+exit+0
++++++++((t+-=+interval))
++++done
++++#+Be+nice,+post+SIGTERM+first.
++++#+The+'exit+0'+below+will+be+executed+if+any+preceeding+command+fails.
++++kill+-s+SIGTERM+$$+&&+kill+-0+$$+%7C%7C+exit+0
++++sleep+$delay
++++kill+-s+SIGKILL+$$
)+2>+/dev/null+&

exec+"$@"|1504763|1504764|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|T|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|U|8|@]|9|@]|A|$]]|$1|L|3|M|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|N|3|-4|5|6|7|W|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|X|8|@]|9|@]|A|$]]]|P|$]]

Try using timeout3 script is very robust and I used a lot without problems on different situations. 
Example to wait just 3 seconds trying to check if ssh port is open.

<pre><code>&gt; echo QUIT &gt; quit.txt
&gt; ./timeout3 -t 3 telnet HOST 22 &lt; quit.txt 
</code></pre>

outputs: you can grep for "Connected" or "Terminated"

timeout3 file contents:

#

<pre><code>#!/bin/bash
#
# The Bash shell script executes a command with a time-out.
# Upon time-out expiration SIGTERM (15) is sent to the process. If the signal
# is blocked, then the subsequent SIGKILL (9) terminates it.
#
# Based on the Bash documentation example.
# If you find it suitable, feel free to include
# anywhere: the very same logic as in the original examples/scripts, a
# little more transparent implementation to my taste.
#
# Dmitry V Golovashkin &lt;Dmitry.Golovashkin@sas.com&gt;

scriptName="${0##*/}"
declare -i DEFAULT_TIMEOUT=9
declare -i DEFAULT_INTERVAL=1
declare -i DEFAULT_DELAY=1
# Timeout.
declare -i timeout=DEFAULT_TIMEOUT

# Interval between checks if the process is still alive.
declare -i interval=DEFAULT_INTERVAL

# Delay between posting the SIGTERM signal and destroying the process by SIGKILL.
declare -i delay=DEFAULT_DELAY

function printUsage() {
 cat &lt;&lt;EOF

Synopsis
 $scriptName [-t timeout] [-i interval] [-d delay] command
 Execute a command with a time-out.
 Upon time-out expiration SIGTERM (15) is sent to the process. If SIGTERM
 signal is blocked, then the subsequent SIGKILL (9) terminates it.

 -t timeout
 Number of seconds to wait for command completion.
 Default value: $DEFAULT_TIMEOUT seconds.

 -i interval
 Interval between checks if the process is still alive.
 Positive integer, default value: $DEFAULT_INTERVAL seconds.

 -d delay
 Delay between posting the SIGTERM signal and destroying the
 process by SIGKILL. Default value: $DEFAULT_DELAY seconds.

As of today, Bash does not support floating point arithmetic (sleep does),
therefore all delay/time values must be integers.
EOF
}

# Options.
while getopts ":t:i:d:" option; do 
 case "$option" in
 t) timeout=$OPTARG ;;
 i) interval=$OPTARG ;;
 d) delay=$OPTARG ;;
 *) printUsage; exit 1 ;;
 esac
done
shift $((OPTIND - 1))

# $# should be at least 1 (the command to execute), however it may be strictly
# greater than 1 if the command itself has options.

if (($# == 0 || interval &lt;= 0)); then 
 printUsage
 exit 1
fi

# kill -0 pid Exit code indicates if a signal may be sent to $pid process.
(
 ((t = timeout))

 while ((t &gt; 0)); do
 sleep $interval
 kill -0 $$ || exit 0
 ((t -= interval))
 done
 # Be nice, post SIGTERM first.
 # The 'exit 0' below will be executed if any preceeding command fails.
 kill -s SIGTERM $$ &amp;&amp; kill -0 $$ || exit 0
 sleep $delay
 kill -s SIGKILL $$
) 2&gt; /dev/null &amp;

exec "$@"
</code></pre>

#

I have a unix shell script which test ftp ports of multiple hosts listed in a file.

<pre><code>for i in `cat ftp-hosts.txt`
 do
 echo "QUIT" | telnet $i 21
done
</code></pre>

In general this scripts works, however if i encounter a host which does not connect, i.e telnet is "Trying...", how can I reduce this wait time so it can test the next host ?

how do i reduce timeout on unix telnet on connection

我有一个unix shell脚本，它测试文件中列出的多个主机的ftp端口。for i in `cat ftp-hosts.txt`        do        echo "QUIT" | telnet $i 21done一般来说，这个脚本是有效的，但是，如果我遇到一个主机没有连接，即telnet正在“尝试...”...

问如何减少unix telnet连接时的超时
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