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Full Discussion: Regular Exression Confusion
Top Forums Shell Programming and Scripting Regular Exression Confusion Post 302212730 by zaxxon on Tuesday 8th of July 2008 08:01:07 AM
Old 07-08-2008
I understood what you want, but to explain the ?, I read about it and fooled around, which might explain it a bit:

Code:
echo -e "November" | egrep Nov\(ember\)\?
November
echo -e "Nov" | egrep Nov\(ember\)\?
Nov
echo -e "Noveember" | egrep Nov\(ember\)\?
Noveember
echo -e "No" | egrep Nov\(ember\)\?
echo -e "Novrebm" | egrep Nov\(ember\)\?
Novrebm

So it is as the description says, none or one occurence. Here it is a group of characters, but they interpret as single characters, not as a complete string.

So much for that.
 

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regex(3)						     Library Functions Manual							  regex(3)

Name
       re_comp, re_exec - regular expression handler

Syntax
       char *re_comp(s)
       char *s;

       re_exec(s)
       char *s;

Description
       The  subroutine	compiles  a string into an internal form suitable for pattern matching.  The subroutine checks the argument string against
       the last string passed to

       The subroutine returns 0 if the string s was compiled successfully; otherwise a string containing an  error  message  is  returned.  If	is
       passed 0 or a null string, it returns without changing the currently compiled regular expression.

       The  subroutine returns 1 if the string s matches the last compiled regular expression, 0 if the string s failed to match the last compiled
       regular expression, and -1 if the compiled regular expression was invalid (indicating an internal error).

       The strings passed to both and may have trailing or embedded newline characters; they are terminated by	nulls.	 The  regular  expressions
       recognized are described in the manual entry for given the above difference.

Diagnostics
       The subroutine returns -1 for an internal error.

       The subroutine returns one of the following strings if an error occurs:

       No previous regular expression
       Regular expression too long
       unmatched (
       missing ]
       too many () pairs
       unmatched )

See Also
       ed(1), ex(1), egrep(1), fgrep(1), grep(1)

																	  regex(3)
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