SSH, The Secure Shell: The Definitive Guide, 2nd Edition

Character Sets for Egrep and ZSH_FILEGLOB

A character set starts with [ and ends at non-escaped ] that is not part of a POSIX character set specifier and that does not follow immediately after [.

The following characters have a special meaning and need to be escaped if meant literally:

- (minus sign)

A range operator, except immediately after [ where it loses its special meaning.

^ or ! (latter applies to ZSH_FILEGLOB)

If immediately after the starting [, denotes a complement: the whole character set will be complemented. Otherwise, literal.

[:alnum:]

Characters for which isalnum returns true (see ctype.h).

[:alpha:]

Characters for which isalpha returns true (see ctype.h).

[:cntrl:]

Characters for which iscntrl returns true (see ctype.h).

[:digit:]

Characters for which isdigit returns true (see ctype.h).

[:graph:]

Characters for which isgraph returns true (see ctype.h).

[:lower:]

Characters for which islower returns true (see ctype.h).

[:print:]

Characters for which isprint returns true (see ctype.h).

[:punct:]

Characters for which ispunct returns true (see ctype.h).

[:space:]

Characters for which isspace returns true (see ctype.h).

[:upper:]

Characters for which isupper returns true (see ctype.h).

[:xdigit:]

Characters for which isxdigit returns true (see ctype.h).

Example

    [[:xdigit:]XY]

is typically equivalent to:

    [0123456789ABCDEFabcdefXY] .

It is also possible to include the predefined escaped character sets into a newly defined one, so:

    [\d\s]

matches digits and whitespace characters.