shell variable COLUMNS

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Jøhnny Fävòrítê (it means "halo, then resonate") - 26 Sep 2004 02:43 GMT

i've noticed that the shell variable COLUMNS get set correctly in the
macosx shell. if i set a terminal window to 120 columns, then type
"echo $COLUMNS" at the prompt, it will print 120, just as i'd expect.

so now i'd like to make use of that value in my command-line programs,
so i can know how many columns of output to print before word-wrapping.
alas, getenv("COLUMNS") returns a null pointer, and so does
getenv("columns"). i know i'm using the function right, because
getenv("PATH") returns the string i'd expect. what the heck? i fooled
around a little, and the environment passed to a command-line program
seems to be much reduced from the variables available to an interactive
shell.

does anybody know how i can get the COLUMNS value associated with the
shell that a command-line program is running in?

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Jøhnny Fävòrítê (it means "halo, then resonate") - 26 Sep 2004 04:24 GMT

> does anybody know how i can get the COLUMNS value associated with the
> shell that a command-line program is running in?

answered my own question, via a half-hour of googling. man, how did
anybody *ever* program before the web? this code will do it:

winsize size;
int stat;

memset(&size, 0, sizeof(size));
stat = ioctl(STDOUT_FILENO, TIOCGWINSZ, &size);

if (stat == 0)
{
// make use of size.ws_col, size.ws_row, etc.
}

the ioctl() call will fail if your program isn't connected to a live
terminal, which can happen if it's run by being double-clicked in a
finder window for instance, so testing 'stat' before using the 'size'
struct is important. you'll have to include <sys/ioctl.h> and possibly
other headers.

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Mike Hall - 26 Sep 2004 06:43 GMT

JÃ¸hnny FÃ¤vÃ²rÃtÃª it means halo, then resonate" wrote:

>JÂ¿hnny FÂvÂrÂtÂ (it means "halo, then resonate") wrote:
>> does anybody know how i can get the COLUMNS value associated with the
>> shell that a command-line program is running in?

Yes, just 'export' it, so child processes can see it.

$ echo $COLUMNS
80

$ set | grep COL
COLUMNS=80

$ env | grep COL
$

The shell variable is 'set' for the current shell, but it's not in the exported
environment available to the children. 'export COLUMNS' (or whatever
for csh, tcsh), and the children will see it, and 'getenv' will be happy to
give you the value.

Or, if you really like 'ioctl's, that's the other way to go.
Can also use 'signal' to catch SIGWINCH signals.

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Jøhnny Fävòrítê (it means "halo, then resonate") - 26 Sep 2004 10:07 GMT

> Yes, just 'export' it, so child processes can see it.

that would require everybody who uses the program to have a special bash
start-up script though, right? yucko. at least i know it's possible to
do it that way, though.

> Can also use 'signal' to catch SIGWINCH signals.

do those signals fire whenever the terminal size changes? that would be
handy.

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Miro Jurisic - 26 Sep 2004 17:19 GMT

> > Can also use 'signal' to catch SIGWINCH signals.
>
> do those signals fire whenever the terminal size changes? that would be
> handy.

Yes.

meeroh

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Mac Forum / Programming / Mac Programming / September 2004

shell variable COLUMNS