regex question using egrep Post: 302539754

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Top Forums Shell Programming and Scripting regex question using egrep Post 302539754 by alister on Monday 18th of July 2011 02:35:11 PM

07-18-2011

Registered User

Quote:

Originally Posted by shamrock

this should work...

Code:

ls -latr | egrep "[aA-zZ]+([0-9])?[0-9]$"

That bracket expression is quite odd and almost certainly incorrect. The a and Z are each included twice, once within the range expression and once without. Since range expressions are undefined outside of the POSIX locale, it's safe to assume that this is intended to run in that locale. A-z in the POSIX locale, aside from including all of the upper case and lower case letters in the English alphabet, also includes a few other characters: <left-square-bracket>, <backslash>, <right-square-bracket>, <circumflex>, <underscore>, <grave-accent>.

Why are there six characters located between the upper and lower case alphabets? They pad the beginning of the lowercase alphabet so that it's exactly 32 positions above the beginning of the uppercase alphabet. Simply flipping a single bit is then sufficient to convert between upper and lower case.

POSIX locale collation sequence:
http://pubs.opengroup.org/onlinepubs...ag_07_03_02_06

I suggest sticking with [A-Za-z] if a POSIX range expression is desired or the [[:alpha:]] character class for any locale.

Regards,
Alister

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LEARN ABOUT LINUX

toupper

TOUPPER(3)						     Linux Programmer's Manual							TOUPPER(3)

NAME

       toupper, tolower - convert letter to upper or lower case

SYNOPSIS

       #include <ctype.h>

       int toupper(int c);
       int tolower(int c);

DESCRIPTION

       toupper() converts the letter c to upper case, if possible.

       tolower() converts the letter c to lower case, if possible.

       If c is not an unsigned char value, or EOF, the behavior of these functions is undefined.

RETURN VALUE

       The value returned is that of the converted letter, or c if the conversion was not possible.

CONFORMING TO

       C89, C99, 4.3BSD.

BUGS

       The  details  of  what constitutes an uppercase or lowercase letter depend on the current locale.  For example, the default "C" locale does
       not know about umlauts, so no conversion is done for them.

       In some non-English locales, there are lowercase letters with no corresponding uppercase equivalent; the German sharp s is one example.

SEE ALSO

       isalpha(3), setlocale(3), towlower(3), towupper(3), locale(7)

COLOPHON

       This page is part of release 3.27 of the Linux man-pages project.  A description of the project, and information about reporting bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

GNU
								    1993-04-04								TOUPPER(3)

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