什么';在UNIX中,$@和$*之间的区别是什么?
在UNIX中,什么';在UNIX中,$@和$*之间的区别是什么?,unix,shell,variables,Unix,Shell,Variables,在UNIX中,$@和$*之间有什么区别?当在脚本中回响时,它们似乎都产生相同的输出。请参见“特殊参数”下的bash手册页 Special Parameters The shell treats several parameters specially. These parameters may only be referenced; assignment to them is not allowed. * Expands to
$@
和$*
之间有什么区别?当在脚本中回响时,它们似乎都产生相同的输出。请参见“特殊参数”下的bash手册页
Special Parameters
The shell treats several parameters specially. These parameters may
only be referenced; assignment to them is not allowed.
* Expands to the positional parameters, starting from one. When
the expansion occurs within double quotes, it expands to a sin‐
gle word with the value of each parameter separated by the first
character of the IFS special variable. That is, "$*" is equiva‐
lent to "$1c$2c...", where c is the first character of the value
of the IFS variable. If IFS is unset, the parameters are sepa‐
rated by spaces. If IFS is null, the parameters are joined
without intervening separators.
@ Expands to the positional parameters, starting from one. When
the expansion occurs within double quotes, each parameter
expands to a separate word. That is, "$@" is equivalent to "$1"
"$2" ... If the double-quoted expansion occurs within a word,
the expansion of the first parameter is joined with the begin‐
ning part of the original word, and the expansion of the last
parameter is joined with the last part of the original word.
When there are no positional parameters, "$@" and $@ expand to
nothing (i.e., they are removed).
一个区别在于它们如何处理输出上的IFS变量
#!/bin/sh
echo "unquoted asterisk " $*
echo "quoted asterisk $*"
echo "unquoted at " $@
echo "quoted at $@"
IFS="X"
echo "IFS is now $IFS"
echo "unquoted asterisk " $*
echo "quoted asterisk $*"
echo "unquoted at " $@
echo "quoted at $@"
如果您这样运行:/demo abc def ghi
,您将得到以下输出:
unquoted asterisk abc def ghi
quoted asterisk abc def ghi
unquoted at abc def ghi
quoted at abc def ghi
IFS is now X
unquoted asterisk abc def ghi
quoted asterisk abcXdefXghi
unquoted at abc def ghi
quoted at abc def ghi
请注意,如果将更改为“X”,则(仅)“带引号的星号”行将在每个“单词”之间显示一个X。如果IFS
的值包含多个字符,则仅第一个字符用于此目的
此功能还可用于其他阵列:
$ array=(123 456 789)
$ saveIFS=$IFS; IFS="|"
$ echo "${array[*]}"
123|456|789
$ IFS=$saveIFS
使用“$@”
比使用$*
更安全。当您使用多字字符串作为shell脚本的参数时,只有“$@”
将每个引用的参数解释为单独的参数
正如上面的输出所示,如果您使用$*
,shell会对参数进行错误计数。请参阅。这个答案明确地涵盖了$@
和$*
之间的差异(即使问题没有)。关键的区别在于引号下的行为——“$*”
和“$@”
之间的区别。
for i in "$@"
do
echo $i # loop $# times
done
for i in "$*"
do
echo $i # loop 1 times
done