使用#或%替換shell中的變量
定義變量：
pth=/abc/aab/abcabc/abcd/cb.txt
變量替換（支持通配符但不支持正則表達式）：
${var#pattern}：刪除變量var中左邊第一個能匹配到pattern左邊的字符
# echo ${pth#*bc}
/aab/abcabc/abcd/cb.txt
${var##pattern}：刪除變量var中左邊最后一個能匹配到pattern左邊的字符
# echo ${pth##*abcd}
/cb.txt
${var%pattern}：刪除變量var中右邊第一個能匹配到pattern右邊的字符
# echo ${pth%ab*}
/abc/aab/abcabc/
${var%pattern}：刪除變量var中右邊第一個能匹配到pattern右邊的字符
# echo ${pth%%ab*}
/
測試通配符和正則表達式：
pth=/abc/aab/abcabc1/abcd/cb.txt
# echo ${pth##*abc[![:digit:]]}
/cb.txt
# echo ${pth##abc+*}
/abc/aab/abcabc1/abcd/cb.txt
記憶：鍵盤上#在%左邊，所以#是去掉左邊的字符，%是去掉右邊的字符，兩個總比一個長
切片
# echo ${pth}
/abc/aab/abcabc/abcd/cb.txt
${var:start:[stop]}：從下標[start,stop)提取變量，下標從0開始，stop可以不給，表示取到結尾。注意是左閉右開的區間，
# 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
變量替換
${var/pattern_string/target_string} ：將匹配的第一個pattern_string變為target_string
# echo ${pth/ab/}
/c/a/cc/cd/cb.txt
${var/pattern_string/target_string} ：將匹配的所有pattern_string變為target_string
# echo ${pth//ab/}
/c/a/cc/cd/cb.txt
賦值變量
${var-target_string} ：假如$var沒有設置，使用target_string作為返回值。(空值和非空值不做處理)
# 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沒有設置或者為空值，使用target_string 作為返回值。(非空值不做處理)
# 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為非空值或者為空值，使用target_string 作為返回值。(沒有設定時不做處理)
# 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為非空值，使用target_string 作為返回值。(空值和未設定時不做處理)
# 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} ：當var未設置時，使用target_string作為返回值，並且將target_string負值給var。（空值和非空值不做處理）
# 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} ：當var未設置或為空值時，將target_string輸出至標准錯誤（非空值不做處理）
# 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沒有設定，將target_string輸出至標准錯誤（空值和非空值不做處理）
獲取變量長度 ${#var}
# path=/usr/bin/abc # echo ${#path} 12
數組操作
定義數組
# array=("abc" "bcd" "abccd" "acde")
獲取數組的所有元素 ${array[@]} 或者 ${array[*]}
# echo ${array[@]} abc bcd abccd acde # echo ${array[*]} abc bcd abccd acde
獲取數組元素個數 ${#array}
# echo ${#array} 3
獲取數組中某個元素的長度 ${#array[下標]}
# echo ${#array[2]}
5
給數組的某個元素賦值array[下標]=value
# array[1]="def" # echo ${array[*]} abc def abccd acde
刪除數組中的元素 unset array[下標]
# unset array[0] # echo ${array[*]} def abccd acde
數組分片訪問 ${array[@]:n:m} 從第n個元素開始，取m個元素
# echo ${array[*]}
def abccd acde
# echo ${array[*]:1:2}
def abccd
替換數組元素內容
# echo ${array[*]}
def abccd acde
# echo ${array[2]/c/f} 將第二個元素的第一個c替換成f
abfcd
# echo ${array[2]//c/f} 將第二個元素中所有的c替換成f
abffd