Peter Eisentraut wrote:
Bruce Momjian wrote:
I checked the use of COLUMNS and it seems bash updates the environment
variable when a window is resized.  I added ioctl(TIOCGWINSZ) if COLUMNS
isn't set.  We already had a call in print.c for detecting the
number of rows on the screen to determine if the pager should
be used. Seems COLUMNS should take precedence over ioctl(), right?

Considering that the code to determine the row count is undisputed so far, the column count detection should work the same. That is, we might not need to look at COLUMNS at all. Unless there is a use case for overriding the column count (instead of just turning off the wrapping).
I asked the folks over at "Experts Exchange" to test the behavior of the ioctl and $COLUMNS on various platforms. I'd been told that I would face huge problems if a console was resized. But the results were pretty consistent, and nothing had problems with resize:

It appears impossible to override $COLUMNS, on some platforms as the readline call sets it.
On many platforms $COLUMNS is null until the call to readline.
OSX does not set $COLUMNS at all.

In short, I recommend the ioctl instead. In order to provide a way to wrap output to a pipe, I think a different mechanism will have to be found.


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