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Re: Request to a new feature on read

From: Dan Douglas
Subject: Re: Request to a new feature on read
Date: Thu, 16 Apr 2015 10:07:30 -0500

On Thu, Apr 16, 2015 at 9:50 AM, Greg Wooledge <address@hidden> wrote:
> I don't see why such features should be compiled into bash's read builtin.
> I'd have no problem with adding better splitting/joining/parsing features
> in a more general context, probably operating on a string variable, but
> certainly not operating on a file descriptor.

I don't think they should be part of `read` either. Some way to extend
the BASH_REMATCH mechanism would be better.
> Doesn't the underlying C library only guarantee you a single character of
> lookahead when reading?  (Or maybe a single byte.  I'm way out of date.
> My knowledge of C comes from the days when char = byte.)  You can't do
> all this fancy perl-RE-style lookahead stuff on a stream with only a
> single byte/char of lookahead.

Hm, maybe you're referring to ungetc? IIRC one byte is the only
guarantee when dealing with pipes. I don't really care about having it
pattern match while reading a stream. To make that work well would
probably involve mmap (and even then, only on regular files).

Probably the most portable way to support "fancier" regex is to call
into std::regex. Any system with a modern C++ compiler should support
ECMAScript regex, which is close to a superset of ERE.

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