Posix Character Sets difference between [[:blank:]] and [[:space:]]?

Question

On this website it says:

[[:blank:]]     space and tab characters
[[:space:]]     whitespace characters

What's the difference between space and tab characters and whitespace characters? To me, they almost seem the same.

Solution

The [[:space:]] class is a superset of [[:blank:]] which additionally (apart from the space and tab of [[:blank:]]) includes

• the newline character (\n, line feed on Unix, ASCII code 10),
• vertical tab (\v, ASCII code 11),
• form feed (\f, ASCII code 12), and
• carriage return (\r, ASCII code 13).

... in the POSIX locale, that is. Other locales may have additional space characters.

Comments

[Stéphane Chazelas]

IOW, [[:blank:]] is horizontal spacing characters only while [[:space:]] contains all horizontal and vertical spacing characters. See also \h vs \s in perl regular expressions.

[Kusalananda]

@StéphaneChazelas Is \r a vertical spacing character?

[Stéphane Chazelas]

Except for the space character, the [[:space:]] characters in the POSIX locale are all control characters, so the behaviour will vary with the device they are sent to. CR moves the cursor/carriage back to the start of the screen/page so on its own is not really a vertical spacing character, but it's part of the CRLF sequence that is sent to ttys for a line-break so as such can be seen as vertical spacing.

[Stéphane Chazelas]

See also: mail-archive.com/[email protected]/msg02479.html