shell脚本变量操作

使用#或%替换shell中的变量

定义变量：

pth=/abc/aab/abcabc/abcd/cb.txt

变量替换（支持通配符但不支持正则表达式）：

${var#pattern}：删除变量var中左边第一个能匹配到pattern左边的字符

# echo ${pth#*bc}
/aab/abcabc/abcd/cb.txt

${var##pattern}：删除变量var中左边最后一个能匹配到pattern左边的字符

# echo ${pth##*abcd}
/cb.txt

${var%pattern}：删除变量var中右边第一个能匹配到pattern右边的字符

# echo ${pth%ab*}
/abc/aab/abcabc/

${var%pattern}：删除变量var中右边第一个能匹配到pattern右边的字符

# echo ${pth%%ab*}
/

测试通配符和正则表达式：

pth=/abc/aab/abcabc1/abcd/cb.txt

# echo ${pth##*abc[![:digit:]]}
/cb.txt

# echo ${pth##abc+*}
/abc/aab/abcabc1/abcd/cb.txt

记忆：键盘上#在%左边，所以#是去掉左边的字符，%是去掉右边的字符，两个总比一个长

切片

# echo ${pth}
/abc/aab/abcabc/abcd/cb.txt

${var:start:[stop]}：从下标[start,stop)提取变量，下标从0开始，stop可以不给，表示取到结尾。注意是左闭右开的区间，

# echo ${pth:0:4}
/abc

# echo ${pth:4:4}
/aab

# echo ${pth:4}
/aab/abcabc/abcd/cb.txt

# echo ${pth:4}
/aab/abcabc/abcd/cb.txt

变量替换

${var/pattern_string/target_string} ：将匹配的第一个pattern_string变为target_string

# echo ${pth/ab/}
/c/a/cc/cd/cb.txt

${var/pattern_string/target_string} ：将匹配的所有pattern_string变为target_string

# echo ${pth//ab/}
/c/a/cc/cd/cb.txt

赋值变量

${var-target_string} ：假如$var没有设置，使用target_string作为返回值。(空值和非空值不做处理)

# path=/usr/bin/abc
# echo ${path-/usr/local/bin/abc}
/usr/bin/abc

# path=
# echo ${path-/usr/local/bin/abc}

# unset path
# echo ${path-/usr/local/bin/abc}
/usr/local/bin/abc

${var:-target_string} ：假如$var没有设置或者为空值，使用target_string 作为返回值。(非空值不做处理)

# path=/usr/bin/abc

# echo ${path:-/usr/local/bin/abc}
/usr/bin/abc

# path=

# echo ${path:-/usr/local/bin/abc}
/usr/local/bin/abc

# unset path

# echo ${path:-/usr/local/bin/abc}
/usr/local/bin/abc

${var+target_string} ：假如$var为非空值或者为空值，使用target_string 作为返回值。(没有设定时不做处理)

# path=/usr/bin/abc
# echo ${path+/usr/local/bin/abc}
/usr/local/bin/abc

# path=

# echo ${path+/usr/local/bin/abc}
/usr/local/bin/abc

# unset path

# echo ${path+/usr/local/bin/abc}

${var:-target_string} ：假如$var为非空值，使用target_string 作为返回值。(空值和未设定时不做处理)

# path=/usr/bin/abc

# echo ${path:+/usr/local/bin/abc}
/usr/local/bin/abc

# path=

# echo ${path:+/usr/local/bin/abc}

 
# unset path

# echo ${path:+/usr/local/bin/abc}

${var=target_string} ：当var未设置时，使用target_string作为返回值，并且将target_string负值给var。（空值和非空值不做处理）

# path=/usr/bin/abc
# echo ${path=/usr/local/bin/abc}
/usr/bin/abc

# echo ${path=/usr/local/bin/abc}
 

# unset path
# echo ${path=/usr/local/bin/abc}
/usr/local/bin/abc

${var:?target_string} ：当var未设置或为空值时，将target_string输出至标准错误（非空值不做处理）

# path=/usr/bin/abc

# echo ${path:?/usr/local/bin/abc}
/usr/bin/abc

# path=

# echo ${path:?/usr/local/bin/abc}
-bash: path: /usr/local/bin/abc

# unset path

# echo ${path:?/usr/local/bin/abc}
-bash: path: /usr/local/bin/abc

${var:?target_string} ：如果var没有设定，将target_string输出至标准错误（空值和非空值不做处理）

获取变量长度 ${#var}

# path=/usr/bin/abc

# echo ${#path}
12

数组操作

定义数组

# array=("abc" "bcd" "abccd" "acde")

获取数组的所有元素 ${array[@]} 或者 ${array[*]}

# echo ${array[@]}
abc bcd abccd acde

# echo ${array[*]}
abc bcd abccd acde

获取数组元素个数 ${#array}

# echo ${#array}
3

获取数组中某个元素的长度 ${#array[下标]}

# echo ${#array[2]}
5

给数组的某个元素赋值array[下标]=value

# array[1]="def"

# echo ${array[*]}
abc def abccd acde

删除数组中的元素 unset array[下标]

# unset array[0]

# echo ${array[*]}
def abccd acde

数组分片访问 ${array[@]:n:m} 从第n个元素开始，取m个元素

# echo ${array[*]}
def abccd acde

# echo ${array[*]:1:2}
def abccd

替换数组元素内容

# echo ${array[*]}
def abccd acde

# echo ${array[2]/c/f}        将第二个元素的第一个c替换成f
abfcd

# echo ${array[2]//c/f}       将第二个元素中所有的c替换成f
abffd