bash中字符串的处理

bash中字符串的处理

---

1.得到字符串长度
方法一:
$echo ${#variable}
code:

zhyfly: ~$ x="this is a test"
zhyfly: ~$ echo ${#x}
14


方法二:
$expr length "$variable"
code:

zhyfly: ~$x="this is a test"
zhyfly: ~$ expr length "$x"
14


方法三:
$expr "$variable" : ".*"
code:

zhyfly: ~$x="this is a test"
zhyfly: ~$ expr "$x" :".*"
14


2.查找字符串子串位置
方法:
$expr index "$variable" "substring"
code:

zhyfly: ~$x="this is a test"
zhyfly: ~$ expr index "$x" "is"
3
zhyfly: ~$ expr index"$x" "t"
1


(ps:如果出现重复,好象只能查到第一个,第二个,第三个,...,怎么查到呢???)
3.得到字符串子字符串
方法一:
$echo ${variable:position:length}
code:

zhyfly: ~$x="this is a test"
zhyfly: ~$ echo ${x:1:5}
his i


方法二:
$expr substr "$variable" startposition length
code:

zhyfly: ~$x="this is a test"
zhyfly: ~$ expr substr "$x" 1 5
this


(ps:注意方法一和方法二中位置的区别!)
4.匹配正则表达式之匹配长度
方法:
$expr match "$x" "string"
code:

zhyfly: ~$x="this is a test"
zhyfly: ~$ expr match "$x" "his"
0
zhyfly: ~$ expr match"$x" "this"
4
zhyfly: ~$ expr match"$x" "."
1


5.字符串的掐头去尾
方法:
$echo ${variable#startletter*endletter} # #表示掐头,因为键盘上#在$前面,一个表示最小匹配
$echo ${variable##tartletter*endletter} 两个表示最大匹配
$echo ${variable%startletter*endletter} # %表示去尾,因为键盘上%在$后面,一个表示最小匹配
$echo ${variable%%startletter*endletter} 两个表示最大匹配
code:

zhyfly: ~$x="this is a test"
zhyfly: ~$ echo ${x#t}
his is a test
zhyfly: ~$ echo ${x#t*h}
is is a test
zhyfly: ~$ echo ${x#t*s}
is a test

zhyfly: ~$ echo ${x##t*s}
t

zhyfly: ~$ echo ${x%t}
this is a tes
zhyfly: ~$ echo ${x%s*t}
this is a te
zhyfly: ~$ echo ${x%e*t}
this is a t

zhyfly: ~$ echo ${x%%i*t}
th


6.字符(串)的替换
方法:
$echo ${variable/oldletter/newletter} #替换一个
$echo ${variable//oldletter/newletter} #替换所有
code:

zhyfly: ~$x="this is a test"
zhyfly: ~$ echo ${x/i/m}
thms is a test
zhyfly: ~$ echo ${x//i/m}
thms ms a test