linux shell Manipulating Strings

http://www.faqs.org/docs/abs/HTML/string-manipulation.html

连接字符串

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a="abc"
b="def"

echo $a$b
expr index $string $substring
Numerical position in $string of first character in $substring that matches.
     1 stringZ=abcABC123ABCabc

2 echo expr index "$stringZ" C12 # 6 3 # C position. 4 5 echo expr index "$stringZ" 1c # 3 6 # ‘c’ (in #3 position) matches before ‘1’.

This is the near equivalent of _strchr()_ in C.

**ength of Matching Substring at Beginning of String**

expr match "$string" '$substring'
:   $substring is a [regular expression][1].

expr "$string" : '$substring'
:   $substring is a regular expression. 
    
    
      
        
             1 stringZ=abcABC123ABCabc

2 # |——| 3 4 echo expr match "$stringZ" 'abc[A-Z]*.2' # 8 5 echo expr "$stringZ" : 'abc[A-Z]*.2' # 8

substring

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b=${a:12:5}
where 12 is the offset (zero-based) and 5 is the length