Re: tput returns wrong value?

[Thomas Dickey]

On Fri, 22 May 2009, address@hidden wrote:

> Dear maintainers of ncurses,
>
> recently i discovered a strange behavior of tput showing by the following code 
> example.
>
> $cat testscript
> tput cols
> i=$( tput cols )
> echo $i
>
> $./testscript
> 109
> 109
>
> $./testscript 2> /dev/null
> 109
> 80
>
>
> As you can see the variable $i has the wrong value if the stderr chanel is 
> redirected. Maybe this behavior is intended. I found it rather annoying and 
> would know if this is correct.
> At first i thought there is something wrong with bash but since it also fails 
> on zsh i am writing you :-)
>
> I tested it on bash 3.2 and zsh 4.3.9

To get the screensize, ncurses needs a file descriptor which is
connnected to the terminal.  Historically, stdout can be redirected
(so it's not necessarily used for this purpose).  So ncurses uses
stderr to obtain the screensize.

If stderr isn't connected to a terminal, ncurses will return the
values from the terminal description.

> Thanks in advance for thinking about it!
> Sebastian
>
> P.S.
> It only occurs when you put it in a file and execute the script:
>
> $ tput cols; foo=$( tput cols ) ; echo $foo 2> /dev/null
> 109
> 109
>
> See.. it works. So it seems to me that 80 is kind of a default value.
> --
> Neu: GMX FreeDSL Komplettanschluss mit DSL 6.000 Flatrate + Telefonanschluss 
> für nur 17,95 Euro/mtl.!* http://portal.gmx.net/de/go/dsl02
>
>
> _______________________________________________
> Bug-ncurses mailing list
> address@hidden
> http://lists.gnu.org/mailman/listinfo/bug-ncurses

--
Thomas E. Dickey
http://invisible-island.net
ftp://invisible-island.net