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Top Forums Shell Programming and Scripting Regex issue with \s in character class. Post 303042638 by Aia on Thursday 2nd of January 2020 12:29:50 AM
Old 01-02-2020
Quote:
Originally Posted by blackrageous
Anybody have an explanation for why \s doesn't match ' ' in a character class? Here are 3 examples with the final example showing that \s in a character class (demonstrated by using egrep -o) fails:

\s works outside of class..

Code:
# echo " FOO " | egrep -o '\s[A-Z]+\s'
 FOO


Here is a sanity check using ' '...

Code:
# echo " FOO " | egrep -o '[  ][A-Z]+[  ]'
 FOO

Here I try with \s in a character class
Code:
# echo " FOO " | egrep -o '[\s][A-Z]+[\s]'
#

The backslash is not a metacharacter in a POSIX compliant bracket expression. Therefore [\s] will match the characters \ or s instead of white space.
 

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

NAME
iswalpha - test for alphabetic wide character SYNOPSIS
#include <wctype.h> int iswalpha(wint_t wc); DESCRIPTION
The iswalpha() function is the wide-character equivalent of the isalpha(3) function. It tests whether wc is a wide character belonging to the wide-character class "alpha". The wide-character class "alpha" is a subclass of the wide-character class "alnum", and therefore also a subclass of the wide-character class "graph" and of the wide-character class "print". Being a subclass of the wide-character class "print", the wide-character class "alpha" is disjoint from the wide-character class "cntrl". Being a subclass of the wide-character class "graph", the wide-character class "alpha" is disjoint from the wide-character class "space" and its subclass "blank". Being a subclass of the wide-character class "alnum", the wide-character class "alpha" is disjoint from the wide-character class "punct". The wide-character class "alpha" is disjoint from the wide-character class "digit". The wide-character class "alpha" contains the wide-character classes "upper" and "lower". The wide-character class "alpha" always contains at least the letters 'A' to 'Z' and 'a' to 'z'. RETURN VALUE
The iswalpha() function returns nonzero if wc is a wide character belonging to the wide-character class "alpha". Otherwise it returns zero. CONFORMING TO
C99. NOTES
The behavior of iswalpha() depends on the LC_CTYPE category of the current locale. SEE ALSO
isalpha(3), iswctype(3) COLOPHON
This page is part of release 3.44 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
1999-07-25 ISWALPHA(3)

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