Re: Problems with ~ and ~~

[Paul Haahr <haahr@jivetech.com>]

> > ; a = <={~~ (foo.c foo.x bar.h) *.[ch]}
> > ; echo $a
> > foo c bar h
> > 
> > You only assigned a command to a.  The <= in front evaluates the
> > command and substitutes the result in the command line.
> 
>  I don't understand well <= role. Man page says that it is for return
>  value of external command. Doesn't make more sense using `{} or eval
>  in this case?...

` and <= are very similar.  Both evaluate their arguments, and both fill
in values that can be used as command arguments.  ` gets its values from
the output of its argument.  <= gets its values from the ``return value''
of its argument;  the return value of an external command is its exit
status (or exit signal), but the return value of an internal function can
be anything.

It's a fairly messy distinction.  I'm very unhappy with it.  If Unix
didn't have exit statuses, it would probably never have happened.
Instead, I generalized exit statuses in a way they shouldn't have been.

Making ~~ print its results would probably have been the right thing;  it
doesn't, if I remember correctly, because I was concerned about quoting
issues and separators and things like that.  If it had just printed its
results, you could have used ` and it would be easier to see results.

--p