setenv from c

[P. D. Guthrie]

In article <1355 at teddy.UUCP> jpn at teddy.UUCP (John P. Nelson) writes:
>> Is it possible to set a csh environment variable within a C program?
>
>In all the replies to this question, I have not yet seen my favorite techniqe.
>This only works on BSD 4.X (at least as far as I know).  There is an
>undocumented ioctl() which allows you to push data back onto your input queue
>(i.e. simulate characters typed at the terminal).  Using this technique, one
>can stuff strings like "setenv TERM xxx\n" into the parent shell's input.
>
>A fragment of the code that does the work:
>
>#include <sgtty.h>
>
>eatthis(string)
>register char *string;
>    {
>    int pendin = LPENDIN;
>
>    noecho();				/* turn off echo mode */
>    while (*string)
>        {
>        ioctl(0, TIOCSTI, string);	/* do the work */
>        ++string;
>        }
>    echo();				/* turn echo back on */
>    ioctl(0, TIOCLBIS, &pendin);	/* set the pending input flag */
>    }

Undocumented? TTY(4) page 12 (66lines/page).  This call does not exist
on either System 5 or Version 7 - however the hack to put them into the
kernel is about twenty lines.  Oh for this and FIONREAD to be put into
standard SYS V!!!

					Paul Guthrie.