9.2. Manipulating Strings
1、String Length
expr "$string" : '.*'
3、Index这个表达式跟java的用法好像不同
expr index $string $substring
Numerical position in $string of first character in $substring that matches.
5 echo `expr index "$stringZ" 1c` # 3
6 # 'c' (in #3 position) matches before '1'.
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4?{string:position:length}负数参数的用法有点怪
Extracts $length characters of substring from $string at $position.
16 echo ${stringZ:-4} # abcABC123ABCabc
17 # Defaults to full string, as in ${parameter:-default}.
18 # However . . .
19
20 echo ${stringZ:(-4)} # Cabc
21 echo ${stringZ: -4} # Cabc
22 # Now, it works.
23 # Parentheses or added space "escape" the position parameter.
24
25 # Thank you, Dan Jacobson, for pointing this out.
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而且下面这段不懂：
If the $string parameter is "*" or "@", then this extracts a maximum of
$length positional parameters, starting at $position.
1 echo ${*:2} # Echoes second and following positional
parameters.
2 echo ${@:2} # Same as above.
3
4 echo ${*:2:3} # Echoes three positional parameters, starting
at second.
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5、Example 9-12. Emulating getopt其中的字符串处理不甚明了
14 if [ ${1:0:1} = '/' ]
15 then
16 tmp=${1:1} # Strip off leading '/' . . .
17 parameter=${tmp%%=*} # Extract name.
18 value=${tmp##*=} # Extract value.
19 echo "Parameter: '$parameter', value: '$value'"
20 eval $parameter=$value
21 fi
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6、awk处理函数不懂
14 # The awk equivalent of ${string:pos:length} is
substr(string,pos,length).
15 echo | awk '
16 { print substr("'"${String}"'",3,4) # skid
17 }
18 '
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7、9.2.2. Further Discussion进一步讨论的几个例子没看
英语疑问：
1、emulation, getopt
A simple emulation of getopt using substring extraction constructs.