Mastering Linux Shell Scripting - Second Edition

Special character classes

We saw how to match a set of characters using the character class, then we saw how to match a range of characters using character ranges.

Actually, the ERE engine offers ready-to-use classes to match some common sets of characters as follows:

[[:alpha:]]	Matches any alphabetical character
[[:upper:]]	Matches A–Z uppercase only
[[:lower:]]	Matches a–z lowercase only
[[:alnum:]]	Matches 0–9, A–Z, or a–z
[[:blank:]]	Matches space or Tab only
[[:space:]]	Matches any whitespace character: space, Tab, CR
[[:digit:]]	Matches from 0 to 9
[[:print:]]	Matches any printable character
[[:punct:]]	Matches any punctuation character

So, if you want to match uppercase characters, ...