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