Re: How to test if a variable is declared?

[Peng Yu]

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?

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