[[ ... ]], [ ... ], bash, zsh

[[ ... ]], [ ... ], bash, zsh

[Haakon Riiser]

In both bash and zsh, the "-n" operator in [ ... ] is optional,
but in [[ ... ]] it's only optional in bash.  Is there a reason
for this?

Thanks in advance for any response!

-- 
 Haakon

Re: [[ ... ]], [ ... ], bash, zsh

[Björn Lindström]

Haakon Riiser <haakon.riiser@fys.uio.no> writes:

> In both bash and zsh, the "-n" operator in [ ... ] is optional, but in
> [[ ... ]] it's only optional in bash.  Is there a reason for this?

If you use [ ], the test is supposed to work like with test(1). In the
case of zsh this is still handled by a built-in, I don't know how it is
with bash. The [[ syntax is a shell-specific extension, and there are
several differences between the shells on how the are interpreted.

Re: [[ ... ]], [ ... ], bash, zsh

[Haakon Riiser]

[Björn Lindström]

>> In both bash and zsh, the "-n" operator in [ ... ] is optional, but in
>> [[ ... ]] it's only optional in bash.  Is there a reason for this?

> If you use [ ], the test is supposed to work like with test(1). In the
> case of zsh this is still handled by a built-in, I don't know how it is
> with bash. The [[ syntax is a shell-specific extension, and there are
> several differences between the shells on how the are interpreted.

Okay, I thought the [[ ... ]] command was mentioned in POSIX.
Still, it seems strange that [[ ... ]] and [ ... ] would differ
with regard to the -n operator;

  if [[ $INITIALIZED ]]; then
      ...
  fi

reads better than

  if [[ -n $INITIALIZED ]]; then
      ...
  fi

so I just wanted to know why it was decided that -n should not
be optional.  (No, it's not important, but I'd feel better if I
knew the reason. :-)

-- 
 Haakon

Re: [[ ... ]], [ ... ], bash, zsh

[Bart Schaefer]

On Aug 14,  1:08am, Haakon Riiser wrote:
} Subject: Re: [[ ... ]], [ ... ], bash, zsh
}
}   if [[ $INITIALIZED ]]; then
} 
}   if [[ -n $INITIALIZED ]]; then
} 
} so I just wanted to know why it was decided that -n should not
} be optional.

It's not the case that someone decided that -n should not be optional.

It is the case that someone decided that arbitrary non-empty strings
should not be considered equivalent to the value "true", and that the
empty string should not be considered equivalent to "false".

The zsh [[ ]] is based on ksh, not on bash:

$ [[ $INITIALIZED ]]
ksh: syntax error: `$INITIALIZED' missing expression operator

So "someone" is probably David Korn.