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Full Discussion: simplify regular expressions
Top Forums Shell Programming and Scripting simplify regular expressions Post 302579744 by durden_tyler on Tuesday 6th of December 2011 12:12:32 PM
Old 12-06-2011
Quote:
Originally Posted by tarun_agrawal
POSIX expression
[[:alpha:]]
That's not the same as the OP's regex.
[:alpha:] is a POSIX character class for alphabetic characters. So the regex [[:alpha:]] matches a single character in the range a-z or A-Z.

Code:
$
$ # lower case single alphabetic character
$ echo "q" | grep -E "[[:alpha:]]"
q
$
$ # upper case single alphabetic character
$ echo "Q" | grep -E "[[:alpha:]]"
Q
$

[ABCDE] or [A-E] is a single character that is either A, or B, or C, or D, or E. So it will fail for both the examples shown above -

Code:
$
$ # fails for any lower case alphabetic character (because of the case)
$ echo "q" | grep -E "[A-E]"
$
$ # even if it is in the range a-e
$ echo "d" | grep -E "[A-E]"
$
$ # fails for any upper case alphabetic character that is not in the range A-E
$ echo "Q" | grep -E "[A-E]"
$

tyler_durden
 

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re_comp(3C)						   Standard C Library Functions 					       re_comp(3C)

NAME
re_comp, re_exec - compile and execute regular expressions SYNOPSIS
#include <re_comp.h> char *re_comp(const char *string); int re_exec(const char *string); DESCRIPTION
The re_comp() function converts a regular expression string (RE) into an internal form suitable for pattern matching. The re_exec() func- tion compares the string pointed to by the string argument with the last regular expression passed to re_comp(). If re_comp() is called with a null pointer argument, the current regular expression remains unchanged. Strings passed to both re_comp() and re_exec() must be terminated by a null byte, and may include NEWLINE characters. The re_comp() and re_exec() functions support simple regular expressions, which are defined on the regexp(5) manual page. The regular expressions of the form {m}, {m,}, or {m,n} are not supported. RETURN VALUES
The re_comp() function returns a null pointer when the string pointed to by the string argument is successfully converted. Otherwise, a pointer to one of the following error message strings is returned: No previous regular expression Regular expression too long unmatched ( missing ] too many () pairs unmatched ) Upon successful completion, re_exec() returns 1 if string matches the last compiled regular expression. Otherwise, re_exec() returns 0 if string fails to match the last compiled regular expression, and -1 if the compiled regular expression is invalid (indicating an internal error). ERRORS
No errors are defined. USAGE
For portability to implementations conforming to X/Open standards prior to SUS, regcomp(3C) and regexec(3C) are preferred to these func- tions. See standards(5). SEE ALSO
grep(1), regcmp(1), regcmp(3C), regcomp(3C), regexec(3C), regexpr(3GEN), regexp(5), standards(5) SunOS 5.11 26 Feb 1997 re_comp(3C)
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