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Full Discussion: Regular Exression Confusion
Top Forums Shell Programming and Scripting Regular Exression Confusion Post 302212646 by Gaurang033 on Tuesday 8th of July 2008 04:37:30 AM
Old 07-08-2008
Quote:

For
2): A single character is a dot, not a question mark.

For 3):
{1} also stands for minimum. It's the same as {1,}. And even {1,4} will print out every line where at least one "a" is in. There is a very good pocke guide on awk and sed from O'Reilly. They have a good overview on regular expressions in the first few pages, very helpful.
Hi
Thnx for your reply
.
1) But when I refer the book and some other on line articles they says that "?" will print 0 or 1 occurrence of the preceding character ?? ( I was understanding it as exact 0 or exact 1, my mistake Smilie )

But now it seems that "*" and "?" are same. or is there any difference ?? Smilie

2) And what should I do if I need to match the exact number of occurrence in the string. Smilie

i.e. I need to find the string that contains only 2 "a" ( not less then 1 and not more then 2 ).
 

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REGEX(3)						     Library Functions Manual							  REGEX(3)

NAME
re_comp, re_exec - regular expression handler SYNOPSIS
char *re_comp(s) char *s; re_exec(s) char *s; DESCRIPTION
Re_comp compiles a string into an internal form suitable for pattern matching. Re_exec checks the argument string against the last string passed to re_comp. Re_comp returns 0 if the string s was compiled successfully; otherwise a string containing an error message is returned. If re_comp is passed 0 or a null string, it returns without changing the currently compiled regular expression. Re_exec 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 re_comp and re_exec may have trailing or embedded newline characters; they are terminated by nulls. The regular expressions recognized are described in the manual entry for ed(1), given the above difference. SEE ALSO
ed(1), ex(1), egrep(1), fgrep(1), grep(1) DIAGNOSTICS
Re_exec returns -1 for an internal error. Re_comp returns one of the following strings if an error occurs: No previous regular expression, Regular expression too long, unmatched (, missing ], too many () pairs, unmatched ). 3rd Berkeley Distribution May 15, 1985 REGEX(3)
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