bash字符串操作的%/%%/#/##操作符

1. 删除最短的前缀匹配子串：#

格式：${str#${prefix}}

从<str>的最左边开始匹配<prefix>，一旦满足，则删除匹配上的子串。

################### = "aabaabABBABB"
${aabaabABBABB#a}   =  "abaabABBABB"    # match="a"
${aabaabABBABB#aa}  =   "baabABBABB"    # match="aa"
${aabaabABBABB#aab} =    "aabABBABB"    # match="aab"
${aabaabABBABB#ab}  = "aabaabABBABB"    # match=""

#################### = "aabaabABBABB"
${aabaabABBABB#*a}   =  "abaabABBABB"    # match="a"
${aabaabABBABB#*aa}  =   "baabABBABB"    # match="aa"
${aabaabABBABB#*aab} =    "aabABBABB"    # match="aab"
${aabaabABBABB#*ab}  =    "aabABBABB"    # match="aab"

#################### = "aabaabABBABB"
${aabaabABBABB#a*}   =  "abaabABBABB"    # match="a"
${aabaabABBABB#aa*}  =   "baabABBABB"    # match="aa"
${aabaabABBABB#aab*} =    "aabABBABB"    # match="aab"
${aabaabABBABB#ab*}  = "aabaabABBABB"    # match=""

我们看到把*放在后面，结果和没有*是一样的，可以这么理解，因为#运算符本来就是前缀匹配，设想自动就带有*左右结尾。

2. 删除最长的前缀匹配子串：##

#################### = "aabaabABBABB"
${aabaabABBABB##a}   =  "abaabABBABB"    # match="a"
${aabaabABBABB##aa}  =   "baabABBABB"    # match="aa"
${aabaabABBABB##aab} =    "aabABBABB"    # match="aab"
${aabaabABBABB##ab}  = "aabaabABBABB"    # match=""

####################  = "aabaabABBABB"
${aabaabABBABB##*a}   =      "bABBABB"    # match="aabaa"
${aabaabABBABB##*aa}  =      "bABBABB"    # match="aabaa"
${aabaabABBABB##*aab} =       "ABBABB"    # match="aabaab"
${aabaabABBABB##*ab}  =       "ABBABB"    # match="aabaab"

##################### =   "aabaabABBABB"
${aabaabABBABB##a*}   =   ""              # match="aabaabABBABB"
${aabaabABBABB##aa*}  =   ""              # match="aabaabABBABB"
${aabaabABBABB##aab*} =   ""              # match="aabaabABBABB"
${aabaabABBABB##ab*}  =   "aabaabABBABB"  # match=""

3. 删除最短的后缀匹配子串：%

################### = "aabaabBAABAA"
${aabaabBAABAA%A}   = "aabaabBAABA"    # match="A"
${aabaabBAABAA%AA}  = "aabaabBAAB"     # match="AA"
${aabaabBAABAA%BAA} = "aabaabBAA"      # match="BAA"
${aabaabBAABAA%AB}  = "aabaabBAABAA"   # match=""

#################### = "aabaabBAABAA"
${aabaabBAABAA%*A}   = "aabaabBAABA"    # match="A"
${aabaabBAABAA%*AA}  = "aabaabBAAB"     # match="AA"
${aabaabBAABAA%*BAA} = "aabaabBAA"      # match="BAA"
${aabaabBAABAA%*AB}  = "aabaabBAABAA"   # match=""

#################### = "aabaabBAABAA"
${aabaabBAABAA%A*}   = "aabaabBAABA"    # match="A"
${aabaabBAABAA%AA*}  = "aabaabBAAB"     # match="AA"
${aabaabBAABAA%BAA*} = "aabaabBAA"      # match="BAA"
${aabaabBAABAA%AB*}  = "aabaabBA"       # match="ABAA"

4. 删除最长的后缀匹配子串：%%

################### = "aabaabBAABAA"
${aabaabBAABAA%%A}   = "aabaabBAABA"    # match="A"
${aabaabBAABAA%%AA}  = "aabaabBAAB"     # match="AA"
${aabaabBAABAA%%BAA} = "aabaabBAA"      # match="BAA"
${aabaabBAABAA%%AB}  = "aabaabBAABAA"   # match=""

#################### = "aabaabBAABAA"
${aabaabBAABAA%%*A}   = ""              # match="aabaabBAABAA"
${aabaabBAABAA%%*AA}  = ""              # match="aabaabBAABAA"
${aabaabBAABAA%%*BAA} = ""              # match="aabaabBAABAA"
${aabaabBAABAA%%*AB}  = "aabaabBAABAA"  # match=""

#################### = "aabaabBAABAA"
${aabaabBAABAA%%A*}   = "aabaabB"        # match= "AABAA"
${aabaabBAABAA%%AA*}  = "aabaabB"        # match= "AABAA"
${aabaabBAABAA%%BAA*} = "aabaab"         # match="BAABAA"
${aabaabBAABAA%%AB*}  = "aabaabBA"       # match=  "ABAA"