get controlling terminal name
Macro Requirements for glibc (see
_POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE ||
returns a string which is the pathname for the current
controlling terminal for this process. If s is NULL,
a static buffer is used, otherwise s points to a
buffer used to hold the terminal pathname. The symbolic
constant L_ctermid is the maximum number of
characters in the returned pathname.
The pointer to
explanation of the terms used in this section, see
returned may not uniquely identify the controlling terminal;
it may, for example, be /dev/tty.
It is not
assured that the program can open the terminal.
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