Re: Mulit-line aliases and PROMPT_COMMAND

[Linda Walsh]

Dan Douglas wrote:

 The 4.4 changes will make aliases even more interesting.
  

---
Oh?   Why is that?  I.e. what's happening to aliases that
will make them more "interesting"? 


BTW, are you using "interesting" in the same way as the
saying "May you live in interesting times"?

Re: Mulit-line aliases and PROMPT_COMMAND

[Dan Douglas]

On Thu, Jun 2, 2016 at 7:18 PM, Grisha Levit  wrote:
>
> On Thu, Jun 2, 2016 at 6:57 PM, Chet Ramey  wrote:
>>
>> > Since bash 4.3 multi-line aliases interact very strangely
>>
>> And you're the first person to report them.  I guess there aren't a lot of
>> multi-line aliases out there.
>
>
> I wonder if more crazy use cases will come out of the woodwork when RHEL and
> SUSE finally get 4.3..

I think when they're used in an actual script rather than for
interactive convenience multiline aliases are some of the more useful
ones. The 4.4 changes will make aliases even more interesting.

Re: Mulit-line aliases and PROMPT_COMMAND

[Grisha Levit]

On Thu, Jun 2, 2016 at 6:57 PM, Chet Ramey  wrote:

> > Since bash 4.3 multi-line aliases interact very strangely
>
> And you're the first person to report them.  I guess there aren't a lot
> of multi-line aliases out there.
>

I wonder if more crazy use cases will come out of the woodwork when RHEL
and SUSE finally get 4.3..

> All of these will be fixed in bash-4.4.


Thanks for taking a look.

Re: Mulit-line aliases and PROMPT_COMMAND

[Chet Ramey]

On 4/20/16 4:41 PM, Grisha Levit wrote:
> Since bash 4.3 multi-line aliases interact very strangely, especially in 
> connection with PROMPT_COMMAND.

And you're the first person to report them.  I guess there aren't a lot of
multi-line aliases out there.

> 1. PROMPT_COMMAND is executed after every line in the alias, rather than just 
> before the prompt is drawn:
>  
> 2. If PROMPT_COMMAND contains a command substitution (even one that is not 
> executed!) then only the first line of the alias is executed

These two are the same problem.

> 3. If an alias contains a command substitution (this is regardless of 
> PROMPT_COMMAND being set) something really non-sensical happens.

This one actually took some time to track down.  All of these will be fixed
in bash-4.4.

-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRUc...@case.eduhttp://cnswww.cns.cwru.edu/~chet/

Mulit-line aliases and PROMPT_COMMAND

[Grisha Levit]

Since bash 4.3 multi-line aliases interact very strangely, especially in 
connection with PROMPT_COMMAND.

1. PROMPT_COMMAND is executed after every line in the alias, rather than just 
before the prompt is drawn:

alias a=$'echo 1\necho2'
PROMPT_COMMAND='echo $HOSTNAME'

$ a
1
home
2
home
$ 

2. If PROMPT_COMMAND contains a command substitution (even one that is not 
executed!) then only the first line of the alias is executed

alias a=$'echo 1\necho2'
PROMPT_COMMAND='echo ${HOSTNAME-$(hostname)}'

$ a
1
home
$ 

3. If an alias contains a command substitution (this is regardless of 
PROMPT_COMMAND being set) something really non-sensical happens.

alias a=$'echo 1 $(id)\necho 2'

$ a
1 2 id
$ 

For the end user, replacing any multi-line aliases with ';' delimited ones 
should probably work just fine.  I can't think of any use-cases where the 
behavior of one style would be different from another so maybe multi-line 
aliases should be disallowed.