What does [[:print:]] means on the following code?
echo 255 > /sys/devices/platform/[[:print:]]*/hwmon/hwmon[[:print:]]*/pwm1
What is the difference between using [[:print:]]* and only *?
echo 255 > /sys/devices/platform/*/hwmon/hwmon*/pwm1
Is there any known name of this feature, or any place I could read and understand more about?
[[:print:]], in either a glob-style expression or a POSIX-compliant regex, matches any printable character.
The reference for (the simplified, single-character case of) glob expressions is https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_13_01; it references the regular expression portion of the standard at https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_03_05 as being authoritative for square-bracket expressions, which describes [:print:] as one of the character-class expressions that all locales must provide. The details of this specific class are then provided in https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap07.html#tag_07_03_01.
[[:print:]] is a Posix class recognized by all engines today as matching up to
144,544 or less, Unicode characters as of Unicode 14.
The raw representation of that is this UTF-8/32 regex based on UCD.
This matches up to ALL of them. Some engines match less, doesn't matter though,
it is always this or less, never more as of V14.
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