shell中特殊的变量

1、$0示例：

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2、@和$#

[root@play ~]# set -- "I am" handsome oldboy.
[root@play ~]# echo $1
I am
[root@play ~]# echo $2
handsome
[root@play ~]# echo $3
oldboy.
[root@play ~]# echo $#
3
[root@play ~]# echo $*
I am handsome oldboy.
[root@play ~]# echo $@
I am handsome oldboy.
[root@play ~]#  for i in "$*";do echo $i;done
I am handsome oldboy.
[root@play ~]# for i in "$@";do echo $i;done
I am
handsome
oldboy.
[root@play ~]# 

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例子如下：

[root@web01 /server/scripts]# cat oldboy.sh 
echo $0
echo $1 $2 $3 $4 $5 $6 $7 $8 $9 ${10} ${11} ${12} $13 $14 $15
echo $#
echo $*
echo $@
echo $$|tee /tmp/a.log
sleep 30
[root@web01 /server/scripts]# 
[root@web01 /server/scripts]# 
[root@web01 /server/scripts]# 
[root@web01 /server/scripts]# cat kill.sh 
kill `cat /tmp/a.log`

[root@play ~]# OLDBOY="I am oldboy"
[root@play ~]# echo $OLDBOY
I am oldboy
[root@play ~]# echo ${#OLDBOY}
11
[root@play ~]# echo ${OLDBOY:2}
am oldboy
[root@play ~]# echo ${OLDBOY:2:2}
am
[root@play ~]# echo ${OLDBOY:5}
oldboy
[root@play ~]# OLDBOY=abcABC123ABCabc
[root@play ~]# echo $OLDBOY
abcABC123ABCabc
[root@play ~]# echo ${OLDBOY#a*C}
123ABCabc
[root@play ~]# echo ${OLDBOY##a*C}
abc
[root@play ~]# echo ${OLDBOY%a*C}
abcABC123ABCabc
[root@play ~]# echo ${OLDBOY%%a*C}
abcABC123ABCabc
[root@play ~]# echo ${OLDBOY%%a*c}

[root@play ~]# echo ${OLDBOY%a*c}
abcABC123ABC
[root@play ~]# echo ${OLDBOY/abc/oppo}
oppoABC123ABCabc
[root@play ~]# echo ${OLDBOY/oppo/abc}
abcABC123ABCabc
[root@play ~]# echo ${OLDBOY//abc/oppo}
oppoABC123ABCoppo

[root@play ~]# echo ${OLDBOY/%abc/oldgirl}
abcABC123ABColdgirl

获取变量长度的5中方法

[root@play ~]# echo $OLDBOY|wc -L
15
[root@play ~]#  echo ${#OLDBOY}
15
[root@play ~]#  expr length "$OLDBOY"
15
[root@play ~]# echo $OLDBOY|awk '{print length}'
15
[root@play ~]#  echo $OLDBOY|awk '{print length($0)}'
15
[root@play ~]# 

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[root@web01 /server/scripts]# test=lele
[root@web01 /server/scripts]# echo $test
lele
[root@web01 /server/scripts]# result=${test:-unset}
[root@web01 /server/scripts]# echo $result
lele
[root@web01 /server/scripts]# unset test
[root@web01 /server/scripts]# echo $test

[root@web01 /server/scripts]# result=${test:-unset}
[root@web01 /server/scripts]# echo $result
unset

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五种运算方法：推荐用let和小括号

[root@play ~]# a=1
[root@play ~]# let a=a+1
[root@play ~]# echo $a
2

[root@play ~]# a=10
[root@play ~]#  ((a=a+1))
[root@play ~]#  echo $a
11
[root@play ~]#

[root@play ~]# a=10
[root@play ~]# expr $a + 110
120
[root@play ~]# 
[root@play ~]# a=10
[root@play ~]# expr $a + 110
120

`[root@play ~]# a=11`
`[root@play ~]#  echo $[$a+11]`
`22`
```[root@play ~]# c="$[a+11]"
```[root@play ~]# echo $c````
22

[root@play ~]# 
[root@play ~]# a=8
[root@play ~]# declare -i a=a+10
[root@play ~]# echo $a
18
[root@play ~]# 

整数或者小数运算：awk或者bc

`[root@play ~]# echo 1 3|awk '{print $1-$2}'`
-2
`[root@play ~]# echo 1.9 3|awk '{print $1+$2}'`
4.9
`[root@play ~]# echo 1.998 3|awk '{print $1+$2}'`
4.998
`[root@play ~]# echo 1.998 3|awk '{print $1*$2}'`
5.994
`[root@play ~]# echo 1.998 3|awk '{print $1%$2}'`
1.998
[root@play ~]# 

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第六章shell条件测试

`[root@play ~]# test -f a && echo ddd >a ||echo 0`
0
`[root@play ~]# `
[root@play ~]# touch a
[root@play ~]# test -f a && echo ddd >a ||echo 0
[root@play ~]# cat a
ddd
[root@play ~]# 

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