我有一个 unix shell 脚本，可以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 $i 21
done
一般来说，这个脚本可以工作，但是如果我遇到一个没有连接的主机，即 telnet 是“正在尝试...”，我怎样才能减少这个等待时间以便它可以测试下一个主机？
【问题讨论】：
标签： telnet
您是否尝试过使用 netcat (nc) 代替 telnet？它具有更大的灵活性，包括能够设置超时：
echo 'QUIT' | nc -w SECONDS YOUR_HOST PORT
# e.g.
echo "QUIT" | nc -w 5 localhost 21
-w 5 选项将在 5 秒后使连接超时。
【讨论】：
-w 1 时，它只是挂在那里超过 1 秒...
-G 选项用于指定 TCP 连接超时
telnet 切换到nc stackoverflow.com/a/59657648/248616
尝试使用 timeout3 脚本非常健壮，我在不同情况下使用了很多没有问题。 示例仅等待 3 秒以尝试检查 ssh 端口是否打开。
> echo QUIT > quit.txt
> ./timeout3 -t 3 telnet HOST 22 < quit.txt
输出：您可以使用 grep 搜索“已连接”或“已终止”
timeout3 文件内容：
##!/bin/bash
#
# The Bash shell script executes a command with a time-out.
# Upon time-out expiration SIGTERM (15) is sent to the process. If the signal
# is blocked, then the subsequent SIGKILL (9) terminates it.
#
# Based on the Bash documentation example.
# If you find it suitable, feel free to include
# anywhere: the very same logic as in the original examples/scripts, a
# little more transparent implementation to my taste.
#
# Dmitry V Golovashkin <Dmitry.Golovashkin@sas.com>
scriptName="${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 || 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 $$ || exit 0
((t -= interval))
done
# Be nice, post SIGTERM first.
# The 'exit 0' below will be executed if any preceeding command fails.
kill -s SIGTERM $$ && kill -0 $$ || exit 0
sleep $delay
kill -s SIGKILL $$
) 2> /dev/null &
exec "$@"
【讨论】：
使用启动进程来休眠并终止 telnet 进程。大致：
echo QUIT >quit.txt
telnet $i 21 < quit.txt &
sleep 10 && kill -9 %1 &
ex=wait %1
kill %2
# Now check $ex for exit status of telnet. Note: 127 inidicates success as the
# telnet process completed before we got to the wait.
我避免了回声 QUIT | telnet 管道在第一个作业的退出代码方面没有歧义。
此代码未经测试。
【讨论】：
如果你有 nmap
nmap -iL hostfile -p21 | awk '/Interesting/{ip=$NF}/ftp/&&/open/{print "ftp port opened for: "ip}'
【讨论】：
nmap -PS -p "$port" --host-timeout 1501ms "$host" 2>/dev/null | grep '/tcp *open '。 $? 将是 0 表示成功，1 表示关闭/超时。 1501ms 是最小超时时间。
使用 timeout 以在 x 秒内退出，无论操作成功还是失败：
timeout 运行一个有时间限制的命令，启动 COMMAND，然后杀死它 如果 DURATION 后仍在运行。
公式：
timeout <seconds> <operation>
示例：
timeout 5 ping google.com
你的例子：
for i in `cat ftp-hosts.txt`
do
timeout 5 telnet $i 21
done
【讨论】：