Re: How to test if a variable is declared?

[Andreas Kusalananda Kähäri]

On Fri, Mar 13, 2020 at 07:55:55AM -0500, Peng Yu wrote:
> This still prints. It just got redirected to null. So when the variable
> contains a long string, it will use extra CPU for a test that could be made
> more light weight. So there is no way to just test if a variable is
> declared in bash?


Could you say something about your actual real-life use case?  Are you,
for example, developing in bash on some severely restricted embedded
system?  From where does your very long string come from?  What is the
situation in which you need to make a decision based on this particular
test?



> 
> On Fri, Mar 13, 2020 at 6:33 AM Andreas Kusalananda Kähäri <
> address@hidden> wrote:
> 
> > On Fri, Mar 13, 2020 at 06:15:16AM -0500, Peng Yu wrote:
> > > This involves printing something to the screen. Is there something along
> > > the line of [[ that doesn’t print to screen? Thanks.
> >
> > if declare -p foo 2>/dev/null; then
> >    # foo is declared
> > else
> >    # foo is not declared
> > fi
> >
> >
> >
> > >
> > > On Thu, Mar 12, 2020 at 10:07 PM David <address@hidden> wrote:
> > >
> > > > On Fri, 13 Mar 2020 at 13:59, Peng Yu <address@hidden> wrote:
> > > >
> > > > > What is the best way
> > > > > to test whether a viable is declared?
> > > >
> > > > Here's one way:
> > > >
> > > > $ echo "$BASH_VERSION"
> > > > 4.4.12(1)-release
> > > > $ unset v
> > > > $ declare -p v ; echo $?
> > > > bash: declare: v: not found
> > > > 1
> > > > $ declare v
> > > > $ declare -p v ; echo $?
> > > > declare -- v
> > > > 0
> > > > $
> > > >
> > > > --
> > > Regards,
> > > Peng
> >
> > --
> > Andreas (Kusalananda) Kähäri
> > SciLifeLab, NBIS, ICM
> > Uppsala University, Sweden
> >
> > .
> >
> -- 
> Regards,
> Peng

-- 
Andreas (Kusalananda) Kähäri
SciLifeLab, NBIS, ICM
Uppsala University, Sweden

.