Re: bash aesthetics question: special characters in reg exp in [[ ... =~~ ... ]]

On 2024-07-23, Ben Bacarisse <ben@bsb.me.uk> wrote:

Kaz Kylheku <643-408-1753@kylheku.com> writes:

This matters when regexes are used for matching a prefix of the input;
if the regex is interpreted according to the theory should match
the longest possible prefix; it cannot ignore R3, which matches
thousands of symbols, because R2 matched three symbols.

>
This is more a consequence of the different views. The in the formal
theory there is no notion of "matching".  Regular expressions define
languages (i.e. sets of sequences of symbols) according to a recursive
set of rules.  The whole idea of an RE matching a string is from their
use in practical applications.

Under the set view, we can ask, what is the longest prefix of
the input which belongs to the language R1|R2. The answer is the
same for R2|R1, which denote the same set, since | corresponds
to set union.

Broken regular expressions identify the longest prefix, except
when the | operator is used; then they just identify a prefix,
not necessarily longest.

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