Help me to understand some regular expresions usage


 
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# 1  
Old 03-06-2008
Help me to understand some regular expresions usage

Can someone explain me how those restatements are constructed
Code:
        suffix=${name#*.}
        prefix=${main%%+([0-9])}
        num=10#${num}

1. What is the logic to use a reg-expr in variable name
2. In first string - the '#' seems to mean 'everithing after next mached', but the '.' in reg-exp is a one character, here it seems it used litteraly. Why?
3. I guess '%%' means return part that match next expression? Is it correct?
4. Why the '()' used in second string? [0-9] - any digit; '+' one or more times; so, +[0-9] should return consecutive numbers from string?! What is the need in '()'
5. How to understand third line? What is done by that whith string of digits?

Thank you

Last edited by alex_5161; 03-06-2008 at 08:42 PM.. Reason: formatting
# 2  
Old 03-07-2008
Quote:
Originally Posted by alex_5161
Can someone explain me how those
restatements are constructed
Code:
        suffix=${name#*.}
        prefix=${main%%+([0-9])}
        num=10#${num}

1. What is the logic to use a reg-expr in variable name
2. In first string - the '#' seems to mean 'everithing after next
mached', but the '.' in reg-exp is a one character, here it seems it
used litteraly. Why?

You don't use regular expressions in parameter expansion; you use
filename expansion (a.k.a. wildcard) patterns.

See:
POSIX shell parameter expansions
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