[Shell学习笔记]字符串操作

1. #! /bin/bash
3. echo ${a-3}
4. a=2
5. echo ${a-3}
6. a=
7. echo ${a-3}

1. 3
2. 2
3. （空）

1. #! /bin/bash
3. echo ${b:-4}
4. b=
5. echo ${b:-4}
6. b=5
7. echo ${b:-4}

1. 4
2. 4
3. 5

1. #! /bin/bash
3. echo ${c=6}
4. c=
5. echo ${c=6}
6. c=7
7. echo ${c=6}

1. 6
3. 7

1. #! /bin/bash
3. echo ${d:=8}
4. d=
5. echo ${d:=8}
6. d=9
7. echo ${d:=8}

1. 8
2. 8
3. 9

1. #! /bin/bash
3. echo ${e+9}
4. e=
5. echo ${e+9}
6. e=10
7. echo ${e+9}

2. 9
3. 9

1. #! /bin/bash
3. echo ${f:+11}
4. f=
5. echo ${f:+11}
6. f=12
7. echo ${f:+11}

3. 11

1. xiaosi@Qunar:~/company/sh$ str=yoona
2. xiaosi@Qunar:~/company/sh$ echo ${#str}
3. 5
4. xiaosi@Qunar:~/company/sh$ echo ${str:3}
5. na
6. xiaosi@Qunar:~/company/sh$ echo ${str:1:3}
7. oon

（9）${string##substring}：从变量$string的开头（从开头匹配），删除最长匹配$substring的子串    

（11）${string%%substring}：从变量$string的结尾（从末尾匹配），删除最长匹配$substring的子串