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Exclamation mark when using character classes

From: hancooper
Subject: Exclamation mark when using character classes
Date: Fri, 20 Aug 2021 23:33:38 +0000

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Friday, August 20, 2021 8:00 PM, Kerin Millar <kfm@plushkava.net> wrote:

> On Fri, 20 Aug 2021 19:28:25 +0000
> hancooper via Bug reports for the GNU Bourne Again SHell bug-bash@gnu.org 
> wrote:
> > I am using EPOCHREALTIME and then computing the corresponding human 
> > readable form, that can handle
> > changes in locale
> > printf -v second '%(%S)T.%s' "${now%[^[:digit:]]}" "${now#[^[:digit:]]}"
> > printf -v minute '%(%M)T' "${now%[^[:digit:]]}"
> > printf -v hour '%(%H)T' "${now%[^[:digit:]]}"Incidentally, [![:digit:]] 
> > does not work there, you need to use the POSIX-specified caret (^) instead 
> > of an
> > exclamation mark when using character classes. I'm not sure if this is 
> > intentional or a bug in bash; man
> > page doesn't seem to mention it.
> "If an open bracket introduces a bracket expression as in XBD RE Bracket 
> Expression, [...] the <exclamation-mark> character ( '!' ) shall replace the 
> <circumflex> character ( '^' ) in its role in a non-matching list in the 
> regular expression notation."
> So says POSIX on the matter of pattern matching notation. In other words, 
> only the exclamation-mark is POSIX-specified, although bash happens to 
> tolerate the use of a circumflex, in which case it should behave in the exact 
> same way. Are you able to show a concrete example of one behaving differently 
> from the other?

I could do with some help separating the integer and the fractional part from a 
floating point number,
particularly for the situation where the number starts with a period.


    # integer part of time interval
    ts="${t%%[![:digit:]]+([:digit:])}"  # remove longest match from back
                                         # 13.877597, remove .877597

    # fractional part of time interval
    fr="${t##*([:digit:])[![:digit:]]}"  # remove longest match from front
                                         # 13.877597, remove 13.

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