Question

I am trying to find some comprehensive documentation on character classes in regular expressions that could be used while using grep. I tried

info grep
man grep
man 7 regex 

but could not find all the characters classes listed down in the documentation.

I am looking for some comprehensive documentation on regex that grep uses. Is there such a documentation available?

Answer 1

grep has three options for regex -E or --extended-regexp -G or --basic-regexp and -P or --perl-regexp.

Extended / Basic Regex Classes: Follow POSIX Classes

Perl Regex Classes: Follow Perl Classes

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From the command line POSIX regex information can be accessed via man 7 regex where as Perl regex data can be accessed via perldoc perlre