Re: Does libtool need to escape plus signs in egrep expressions?

[Bob Friesenhahn]

On Thu, 28 Jun 2018, Roumen Petrov wrote:
> May be I misunderstand issue.
>
> $ echo ' _head_ABC_a'  | egrep ' _head_[A-Za-z0-9_]+_[ad]l*$'
>  _head_ABC_a
>
> $ echo ' _head_ABC_al'  | egrep ' _head_[A-Za-z0-9_]+_[ad]l*$'
>  _head_ABC_al
>
> but:
> $ echo ' _head__al'  | egrep ' _head_[A-Za-z0-9_]+_[ad]l*$'
> $ echo ' __head_ABC_al'  | egrep ' _head_[A-Za-z0-9_]+_[ad]l*$'
> $ echo ' _head_ABC_zl'  | egrep ' _head_[A-Za-z0-9_]+_[ad]l*$'
>
>
>
> > Are you sure this actually works?
> I'm not expert in regular expressions but according above tests "plus" in RE 
> works - see case _head__al .

It should match a run of alpha-numeric characters including 
underscores.  However, I do see that the expression includes a match 
of literal underscore and then there is a literal underscore so there 
might be something going on with that.  Greedy matching would likely 
absorb a final underscore so it might not be possible to match on that 
final literal underscore.  This might expose differences in behaviors 
between egreps.

Bob
--
Bob Friesenhahn
address@hidden, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/