On Sun, Nov 24, 2024 at 10:51:43PM +1000, Martin D Kealey wrote: > On Sun, 24 Nov 2024 at 18:05, Andreas Kähäri <andreas.kah...@abc.se> wrote: > > > I think the manual is quite clear: > > > > Within [ and ], character classes can be specified > > using the syntax [:class:], where class is one of the > > following classes defined in the POSIX standard: > > alnum alpha ascii blank cntrl digit graph lower print > > punct space upper word xdigit > > > > It says that the syntax "[:class:]" may be used within "[" and "]". > > > > When one already knows how it works, that's obvious, and it's hard to see > how it could mean anything else. > > When one *doesn't *already know how it works, “using the syntax *[:class:]*” > could just as easily mean using *:class:* inside *[…]*. > > (This ambiguity is largely because it does not specify whether *[:class:]* > is the syntax for a character class, or the syntax for a bracket expression > containing a character class. It isn't helped by the phrase “*within [ and > ]*”, which is pretty silly; its most literal reading in English means > “putting something in [ and putting something in ]”, both of which are > impossible. The intention is of course “*between [ and ]*” but that's > slightly ambiguous; I would suggest “*within a bracket expression*”, since > that's what it's called in POSIX §9.3.5 RE Bracket Expression > <https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/V1_chap09.html#tag_09_03_05> > and in POSIX §2.14.1 Patterns Matching a Single Character > <https://pubs.opengroup.org/onlinepubs/9799919799/utilities/V3_chap02.html#tag_19_14_01> > 2.14x > <https://pubs.opengroup.org/onlinepubs/9799919799/utilities/V3_chap02.html#tag_19_14_02>. > Or if that's not clear enough, “*within a […] bracket expression*”.) > > This REALLY needs to be driven home both in the explanation and with > examples, preferably with at least one that illustrates using more than one > character class inside one match group.
A technical manual about a shell is not the place for that. It may be distributed in a separate tutorial. > > How about this: Is this significantly different from how regular expressions usually works to warrant the text to be duplicated in multiple manuals on the user's system (e.g. re_format)? I don't think so. > > Within a […] bracket expression, character classes can be specified using > > the class syntax *[:class:]* (giving a bracket expression syntax of *[*… > > *[:class:]*…*]*), where *class* is one of the following classes defined > > in the POSIX standard: > > > > - *alnum* *alpha* *ascii* *blank* *cntrl* *digit* *graph* *lower* > > *print* *punct* *space* *upper* *word* *xdigit* > > > > There is no limit on the number or order of symbols, range expressions, > > character classes, and equivalence classes that can be used in one […] > > bracket expression. For example *[@[:digit:]#[=c=]$F-L]* will match any > > one of: > > > > - the symbols ‘@’, ‘#’, & ‘$’; or > > - the decimal digits; or > > - the symbols that are “equivalent” to ‘c’ according to the current > > locale > > (in addition to 'c' itself, this typically includes 'C', but may also > > include accented variants such as 'ç', 'Ç', 'č', & 'Č'); > > or > > - the (upper-case) letters ‘F’, ‘G’, ‘H’, ‘I’, ‘J’, ‘K’, & ‘L’. > > > > -Martin -- Andreas (Kusalananda) Kähäri Uppsala, Sweden .
