[[email protected] ceshi]# cat test.sh
#!/bin/bash
# test.sh
echo "-------------ISF is set to \"-seperator\" ------------"
IFS="-seperator"; # 注意 seperator前有一个减号(-)
for i in "[email protected]"; do echo "@ ‘$i‘"; done
for i in "$*"; do echo "* ‘$i‘"; done
echo "-------------ISF is set to null ------------------------"
IFS=
for i in "[email protected]"; do echo "@ ‘$i‘"; done
for i in "$*"; do echo "* ‘$i‘"; done
echo "-------------ISF is unset ------------------------"
unset IFS
for i in "[email protected]"; do echo "@ ‘$i‘"; done
for i in "$*"; do echo "* ‘$i‘"; done
echo ‘---------$* and [email protected] are not put into double quotes(" ")-------‘
for i in [email protected]; do echo "@ ‘$i‘"; done
for i in $*; do echo "* ‘$i‘"; done
test.sh aa bb cc执行的结果如下：
[[email protected] ceshi]# sh test.sh aa bb cc
-------------ISF is set to "-seperator" ------------
@ ‘aa‘
@ ‘bb‘
@ ‘cc‘
* ‘aa-bb-cc‘
-------------ISF is set to null ------------------------
@ ‘aa‘
@ ‘bb‘
@ ‘cc‘
* ‘aabbcc‘
-------------ISF is unset ------------------------
@ ‘aa‘
@ ‘bb‘
@ ‘cc‘
* ‘aa bb cc‘
---------$* and [email protected] are not put into double quotes(" ")-------
@ ‘aa‘
@ ‘bb‘
@ ‘cc‘
* ‘aa‘
* ‘bb‘
* ‘cc‘
由此可见，
1） 当不加双引号("")时, $*,[email protected]被展开时的行为是一样的;
2） 当$*,[email protected]都被放到双引号("")内;
2.1） 如果设置了变量IFS的值并且该值非空, 则$*被展开时使用${IFS}的第一个字符将所有参数(除了参数$0）连接起来, 即"$1c$2c$3c...",其中c表示${IFS}的第一个字符；
2.2） 如果变量IFS为空, 则$*被展开时只是将所有参数(除了参数$0）简单连接起来, 即 “$1$2$3..."
2.3）如果变量IFS没有被定义, 则$*被展开时使用空格字符将所有参数（除了参数$0) 连接起来, 即"$1 $2 $3 ..."
但[email protected]的展开和没有加双引号的情形是一致的。
更多的Shell脚本例子：
#!/bin/bash
set ‘apple pie‘ pears peaches
for i in $* #单引号被去掉，循环单个字符输出#
do echo $i
done
[[email protected] ceshi]# sh test1.sh
apple
pie
pears
peaches
--------------------------------------------------------------
#!/bin/bash
set ‘apple pie‘ pears peaches
for i in "$*" #单引号被去掉，但当作字符串一次输出#
do echo $i
done
[[email protected] ceshi]# sh test2.sh
apple pie pears peaches
-----------------------------------------------------------------
#!/bin/bash
set ‘apple pie‘ pears peaches
for i in [email protected] #单引号被去掉，循环单个字符输出#
do echo $i
done
[[email protected] ceshi]# sh test3.sh
apple
pie
pears
peaches
-----------------------------------------------------------------
#!/bin/bash
set ‘apple pie‘ pears peaches
for i in "[email protected]" #每个位置参数都将当成一个加引号的字符串:"apple pie","pears ","peaches"#
do echo $i
done
[[email protected] ceshi]# sh test4.sh
apple pie
pears
peaches
-----------------------------------------------------------------
test5.sh
sum=0
for var
in "[email protected]"
do
let sum=sum+$var
done
echo "sum=$sum"
./test1.sh 1 2 3
结果为sum=6
-----------------------------------------------------------------
test6.sh
sum=0
for var
in "$*"
do
let sum=sum+$var
done
echo "sum=$sum"
./test2.sh 1 2 3
结果为sum=1
-----------------------------------------------------------------
分析一：
bash -x test1.sh
结果如下：
+ sum=0
+ for var in ‘ "[email protected]" ‘
+ let sum=sum+1
+ for var in ‘ "[email protected]" ‘
+ let sum=sum+2
+ for var in ‘ "[email protected]" ‘
+ let sum=sum+3
+ echo sum=6
sum=6
可以看出for执行了三次，说明for是以""为边界的，因为每个参数是以""被包围的
分析二：
bash -x test2.sh
结果如下：
+ sum=0
+ for var in ‘"$*"‘
+ let sum=sum+1 2 3
+ echo sum=1
sum=1
可以看出循环只执行了一次，说明$*整体是以""包围的，不是每个参数被""包围，因此只执行一次
一个更直接的例子是：
for var
in "a b c"
do
echo "${var}@"
done
打印:
a b [email protected]
for var
in "a" "b" "c"
do
echo "${var}@"
done
打印：
[email protected]
[email protected]
[email protected]