shell变量二 数组和字符串 子串

变量处理

---

子串: 字符串子串, 数组子串; 类似${parameter}[offset:length]即求值后处理数组; 字符数组或字符串数组;

${parameter:offset}
${parameter:offset:length}

• 格式一: parameter[offset:]
• 格式二: length<0 ? parameter[offset:length] : paramter[offset:offset+length]
• 注: offset,length可以为正负数; 正数offset下标,length长度; 负数offset下标, length下标;

offset,length会当成算数表达式进行处理; offset为负数建议空格, :- 则会被错误解析;

下标从0开始; length下标则为半开区间[);

---

字符串子串案例

普通字符串

aaa=bbb0123456789bbb
echo ${aaa:3:10}
echo ${aaa:3:-3}
echo ${aaa: -13:10}
echo ${aaa: -13:-3}

# 0123456789
# 0123456789
# 0123456789
# 0123456789

选项参数字符串

set -- bbb0123456789bbb
echo ${1:3:10}
echo ${1:3:-3}
echo ${1: -13:10}
echo ${1: -13:-3}

# 0123456789
# 0123456789
# 0123456789
# 0123456789

字符串数组

array[0]=bbb0123456789bbb
echo ${array[0]:3:10}
echo ${array[0]:3:-3}
echo ${array[0]: -13:10}
echo ${array[0]: -13:-3}

# 0123456789
# 0123456789
# 0123456789
# 0123456789

@处理入参数组和自定义数组

其他和普通变量相同, 除了length不能为负数;否则报错

入参数组

set -- b b 0 1 2 3 4 5 6 7 8 9 b b b
echo ${@:0}
echo ${@:3:10}
echo ${@:3:-3}
echo ${@: -13:10}
echo ${@: -13:-3}

# ./test.sh b b 0 1 2 3 4 5 6 7 8 9 b b b
# 0 1 2 3 4 5 6 7 8 9
# ./test.sh: line 4: -3: substring expression < 0
# 0 1 2 3 4 5 6 7 8 9
# ./test.sh: line 6: -3: substring expression < 0

自定义数组

array=(b b b 0 1 2 3 4 5 6 7 8 9 b b b)
echo ${array[@]:0}
echo ${array[@]:3:10}
echo ${array[@]:3:-3}
echo ${array[@]: -13:10}
echo ${array[@]: -13:-3}

# b b b 0 1 2 3 4 5 6 7 8 9 b b b
# 0 1 2 3 4 5 6 7 8 9
# ./test.sh: line 4: -3: substring expression < 0
# 0 1 2 3 4 5 6 7 8 9
# ./test.sh: line 6: -3: substring expression < 0

不能作用于图, 得到的结果不确定, 可能不同机器或不同版本的shell结果不一样;