shell 字符串操作

<一> 字符串匹配，提取

字符串长度

${#string}    
expr length $string
expr "$string" : '.*'


匹配字符串开头的子串长度

expr match "$string" '$substring'
          $substring is a regular expression

expr "$string" : '$substring'

str=abcdABCD1234dcba

echo `expr match "$str" 'abcd[A-Z]*.2'` # 10

echo `expr "$str" : 'abcd[A-Z]*.2'`     # 10


索引

expr index $string $substring

str=abcdABCD1234dcba

echo `expr index "$str" CD1` # 7; position of 'C'
echo `expr index "$str" 1c`  # 3； 类似于strchr()


提取子串

${string:position}   在$string中从位置$position开始提取子串.

${string:position:length}   在$string中从位置$position开始提取$length长度的子串

str=abcABC123

echo ${str:0}   # abcABC123
echo ${str:3}   # ABC123
echo ${str:2:4} # cABC

echo ${str:(-4)} # C123
echo ${str: -4}  # C123; 冒号后需空格

如果string 是"*"或"@", 将提取位置参数
echo ${*:2}   #第2个和后边的所有位置参数

expr substr $string $position $length
      在$string中从$position开始提取$length长度的子串.position从1开始计数，非0.
  
   str=abcdefg
   echo `expr substr $str 2 3`          # bcd


expr match "$string" '\($substring\)'  从$string的开始位置提取$substring(re).
expr "$string" : '\($substring\)'

str=abcABC123ABCabc

echo `expr match "$str" '\(.[b-c]*[A-Z]..[0-9]\)'` # abcABC1
echo `expr "$str" : '\(.[b-c]*[A-Z]..[0-9]\)'` # abcABC1
echo `expr "$str" : '\(.......\)'` # abcABC1

expr match "$string" '.*\($substring\)'  从$string结尾提取$substring(re).
expr "$string" : '.*\($substring\)'
   
      echo `expr "$string" : '.*\(......\)'`  从string结尾提取6个字符



<字符串子串削除>

${string#substring}   从string的开头位置截掉最短匹配的$substring.
${string##substring}  截掉最长匹配的substring.
        
       str=abcABC123ABCabc
       echo ${str#a*C}        # 123ABCabc
       echo ${str##a*C}       # abc

${string%substring}   从string的结尾位置截掉最短匹配的$substring.
${string%%substring}  截掉最长匹配的substring.
        
       str=abcABC123ABCabc
       echo ${str%b*c}        # abcABC123ABCa
       echo ${str%%b*c}       # a


<子串替换>

${string/substring/replacement}
         使用$replacement来替换第一个匹配的$substring.
${string//substring/replacement}
         使用$replacement来替换所有匹配的$substring.

str=abcABC123ABCabc
echo ${str/abc/xyz}     # xyzABC123ABCabc
echo ${str//abc/xyz}    # xyzABC123ABCxyz

 

${string/#substring/replacement}
    如果$substring匹配$string的开头部分, 那么就用$replacement来替换$substring.
${string/%substring/replacement}
    如果$substring匹配$string的结尾部分, 那么就用$replacement来替换$substring.

str=abcABC123ABCabc
echo ${str/#abc/XYZ} # XYZABC123ABCabc
echo ${str/%abc/XYZ} # abcABC123ABCXYZ