Re: Regexp Functions

[Aaron Hill]

On 2020-06-09 9:25 am, Michael Gerdau wrote:
> [sent this earlier and forgot to include the list...]
>
> > That definition helps.     I use the Guile manual, the section Regular
> > Expressions is miss leading about what is there.    I only went there
> > because Arron Hill told me about it     And the introduction states "A
> > full description of regular expressions and their syntax is beyond the
> > scope of this manual"; and the URL goes nowhere.   And I would guess
> > knowing what to read elsewhere that is consistent with the guile
> > version Lilypond uses may be a probleblen.   I am open to a good ron
> > cryptic reference?
>
> I personally really like the perlre manpage. It is THE reference for
> all Perl Regular Expressions from which many other current regexp
> engines are derived.

Just be aware that Guile uses GNU's version of POSIX extended regular 
expressions (ERE), which is significantly more limited than 
Perl-compatible regular expressions (PCRE).

GNU adds some features beyond the core POSIX standard, such as 
shorthands for word characters (\w) and whitespace (\s).  But it omits 
the one for digits (\d) that is included in PCRE.  Instead, one must use 
either /[0-9]/ or /[[:digit:]]/, the latter being an example of a POSIX 
character class.

GNU ERE includes support for the {,n} quantifier that matches an item 
between zero and n times; however, quantifiers in POSIX ERE are always 
greedy, whereas PCRE supports lazy and possessive variants.

POSIX ERE permits only basic unnamed capturing groups, although GNU ERE 
does add support for backreferences: /.(.)(.)\2\1/ will match 'xyzzy'.  
However, PCRE additionally handles non-capturing groups, named groups, 
and many forms of lookarounds and conditionals.


-- Aaron Hill