Re: grep -P in OF template Makefile: really useful?

[Mike Miller]

On Sat, Mar 04, 2017 at 23:18:29 +0100, Julien Bect wrote:
> Hi everyone,
> 
> The template Makefile for OF packages
> (https://octave.sourceforge.io/templates/Makefile) contains this line:
> 
> PKG_ADD := $(shell grep -sPho '(?<=(//|\#\#) PKG_ADD: ).*' $(CC_SOURCES)
> $(M_SOURCES))
> 
> It turns out that this can cause problems on some platforms where grep -P is
> not supported [1].
> 
> Could anybody familiar enough with regexps tell me if the -P flag is
> actually useful for this particular regexp?
> 
> If it is, could we find a way to rewrite the regexp that would not require
> PCRE?

I guess you're using the lookbehind syntax to just avoid matching that
part of the line when using the -o option? That looks like overkill to
me. The -h and -o options are also not specified by the POSIX definition
of grep.

IMHO this is a much safer and more portable alternative:

  sed -n 's/^\(##\|\/\/\) PKG_ADD: \(.*\)/\2/p' ...

-- 
mike