redirecting stdout of no/empty command

redirecting stdout of no/empty command

[Isaac Huang]

Hi list,

I noticed a zsh behaviour today. If I tried to run '>/dev/null' (i.e.
stdout redirection of no command at all) on an interactive zsh, the
zsh would actually run a 'cat', and it wouldn't exit until a ^D or ^C.

The same thing on bash seemed to be a no-op. I wonder why zsh would
run 'cat' when it was given no command to run at all.

Please CC me as I'm not on the list. Thanks.

- Isaac

Re: redirecting stdout of no/empty command

[Daniel Shahaf]

Isaac Huang wrote on Fri, Jan 06, 2012 at 11:34:26 -0700:
> Hi list,
> 
> I noticed a zsh behaviour today. If I tried to run '>/dev/null' (i.e.
> stdout redirection of no command at all) on an interactive zsh, the
> zsh would actually run a 'cat', and it wouldn't exit until a ^D or ^C.
> 
> The same thing on bash seemed to be a no-op.

Actually it truncates the file.

$ echo foo>1
$ >1
$ cat 1
$ 

> I wonder why zsh would
> run 'cat' when it was given no command to run at all.
> 

As a shorthand.

See also NULLCMD and READNULLCMD in zshall(1).

> Please CC me as I'm not on the list. Thanks.
> 
> - Isaac

Re: redirecting stdout of no/empty command

[Damien Thébault]

On Fri, Jan 6, 2012 at 19:43, Daniel Shahaf <d.s@daniel.shahaf.name> wrote:
> Isaac Huang wrote on Fri, Jan 06, 2012 at 11:34:26 -0700:
>> Hi list,
>>
>> I noticed a zsh behaviour today. If I tried to run '>/dev/null' (i.e.
>> stdout redirection of no command at all) on an interactive zsh, the
>> zsh would actually run a 'cat', and it wouldn't exit until a ^D or ^C.
>>
>> The same thing on bash seemed to be a no-op.
>
> Actually it truncates the file.
>
> $ echo foo>1
> $ >1
> $ cat 1
> $
>

I have the same behaviour than Isaac:

luke% zsh -f
luke% >file1
[Typing Hello, World^D^D]
luke% cat file1
Hello, World
luke%

(It's not affecting me much since when I need to have empty input, I
use cat /dev/null or echo -n "")

-- 
Damien Thebault

Re: redirecting stdout of no/empty command

[Daniel Shahaf]

Damien Thébault wrote on Fri, Jan 06, 2012 at 20:07:35 +0100:
> On Fri, Jan 6, 2012 at 19:43, Daniel Shahaf <d.s@daniel.shahaf.name> wrote:
> > Isaac Huang wrote on Fri, Jan 06, 2012 at 11:34:26 -0700:
> >> Hi list,
> >>
> >> I noticed a zsh behaviour today. If I tried to run '>/dev/null' (i.e.
> >> stdout redirection of no command at all) on an interactive zsh, the
> >> zsh would actually run a 'cat', and it wouldn't exit until a ^D or ^C.
> >>
> >> The same thing on bash seemed to be a no-op.
> >
> > Actually it truncates the file.
> >
> > $ echo foo>1
> > $ >1
> > $ cat 1
> > $
> >
> 
> I have the same behaviour than Isaac:
> 

So do I.  My earleir mail described bash's behaviour, not zsh's.

> luke% zsh -f
> luke% >file1
> [Typing Hello, World^D^D]
> luke% cat file1
> Hello, World
> luke%
> 
> (It's not affecting me much since when I need to have empty input, I
> use cat /dev/null or echo -n "")
> 
> -- 
> Damien Thebault

Re: redirecting stdout of no/empty command

[Stephane Chazelas]

2012-01-06 20:07:35 +0100, Damien Thébault:
[...]
> (It's not affecting me much since when I need to have empty input, I
> use cat /dev/null or echo -n "")
[...]

The usual way to do it is:

: > foo

-- 
Stephane