场景：test.txt文件内容格式如下（IP Port），测试每个IP的连通性。
# cat test.txt
192.168.116.128 22
192.168.116.129 22
192.168.116.131 22
192.168.116.134 22
实现1：
# cat test.txt | while read ip port; do nc -n -v -z -w 2 $ip $port; done
Connection to 192.168.116.128 22 port [tcp/*] succeeded!
Connection to 192.168.116.129 22 port [tcp/*] succeeded!
Connection to 192.168.116.131 22 port [tcp/*] succeeded!
nc: connect to 192.168.116.134 port 22 (tcp) timed out: Operation now in progress
实现2：
# for i in `cat test.txt | sed 's/ /,/g'`; do eval $(echo $i | awk 'BEGIN{FS=","}{printf("ip=%s;port=%s\n",$1,$2)}'); nc -n -v -z -w 2 $ip $port; done
Connection to 192.168.116.128 22 port [tcp/*] succeeded!
Connection to 192.168.116.129 22 port [tcp/*] succeeded!
Connection to 192.168.116.131 22 port [tcp/*] succeeded!
nc: connect to 192.168.116.134 port 22 (tcp) timed out: Operation now in progress
总结：
可见实现1比较快捷，其主要用到了read，关于read的用法还有挺多，详见man bash。
read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p
prompt] [-t timeout] [-u fd] [name ...]
One line is read from the standard input, or from the file
descriptor fd supplied as an argument to the -u option, and the
first word is assigned to the first name, the second word to the
second name, and so on, with leftover words and their interven-
ing separators assigned to the last name. If there are fewer
words read from the input stream than names, the remaining names
are assigned empty values. The characters in IFS are used to
split the line into words. The backslash character (\) may be
used to remove any special meaning for the next character read
and for line continuation. Options, if supplied, have the fol-
lowing meanings:
-a aname
The words are assigned to sequential indices of the array
variable aname, starting at 0. aname is unset before any
new values are assigned. Other name arguments are
ignored.
-d delim
The first character of delim is used to terminate the
input line, rather than newline.
-e If the standard input is coming from a terminal, readline
(see READLINE above) is used to obtain the line. Read-
line uses the current (or default, if line editing was
not previously active) editing settings.
-i text
If readline is being used to read the line, text is
placed into the editing buffer before editing begins.
-n nchars
read returns after reading nchars characters rather than
waiting for a complete line of input, but honor a delim-
iter if fewer than nchars characters are read before the
delimiter.
-N nchars
read returns after reading exactly nchars characters
rather than waiting for a complete line of input, unless
EOF is encountered or read times out. Delimiter charac-
ters encountered in the input are not treated specially
and do not cause read to return until nchars characters
are read.
-p prompt
Display prompt on standard error, without a trailing new-
line, before attempting to read any input. The prompt is
displayed only if input is coming from a terminal.
-r Backslash does not act as an escape character. The back-
slash is considered to be part of the line. In particu-
lar, a backslash-newline pair may not be used as a line
continuation.
-s Silent mode. If input is coming from a terminal, charac-
ters are not echoed.
-t timeout
Cause read to time out and return failure if a complete
line of input is not read within timeout seconds. time-
out may be a decimal number with a fractional portion
following the decimal point. This option is only effec-
tive if read is reading input from a terminal, pipe, or
other special file; it has no effect when reading from
regular files. If timeout is 0, read returns success if
input is available on the specified file descriptor,
failure otherwise. The exit status is greater than 128
if the timeout is exceeded.
-u fd Read input from file descriptor fd.
If no names are supplied, the line read is assigned to the vari-
able REPLY. The return code is zero, unless end-of-file is
encountered, read times out (in which case the return code is
greater than 128), or an invalid file descriptor is supplied as
the argument to -u.
