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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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iso2022(5)							File Formats Manual							iso2022(5)

NAME
iso2022, iso-2022, ISO-2022 - A character encoding mechanism standardized by the International Standards Organization (ISO) DESCRIPTION
The ISO-2022 standard defines a mechanism for handling single-byte and multibyte characters. The standard specifies four classes of charac- ter sets: The 94-charset class, which contains character sets with 94 positions (single-byte characters). Examples are the ASCII and JIS X0201 character sets. The 96-charset class, which contains character sets with 96 positions (single-byte characters). Examples are the ISO Latin series of character sets. The 94x94-charset class, which contains character sets with 94x94 positions (2-byte characters). Examples are the GB 2312 and the CNS 11643 character sets. The 96x96-charset class, which contains character sets with 96x96 positions (2-byte characters). In the ISO-2022 standard, four registers, called G0, G1, G2 and G3, are used to reference a character set. Before a character set can be used, the character set must be assigned, or designated, to one of these registers. The designation of a character set is done by using an escape sequence in the following format: ESC [I] F In this format: Is an intermediate character that is used to designate a character set to one of the registers (G0, G1, G2, oR G3). Is a unique final character of a particular character set. The designation of a character set, whose final character is F, to different registers is as follows: Designates a multibyte character set (94x94 or 96x96) to G0. Designates a character set in the 94-charset class to G0. Designates a character set in the 94-charset class to G1. Designates a character set in the 94-charset class to G2. Designates a character set in the 94-charset class to G3. Designates a character set in the 96-charset class to G1. Designates a character set in the 96-charset class to G2. Designates a character set in the 96-charset class to G3. SEE ALSO
Commands: locale(1) Others: ascii(5), i18n_intro(5), iso2022jp(5), l10n_intro(5) iso2022(5)

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