ISATTY(3POSIX)

💖 ISATTY(3POSIX) — bestie, is this a terminal or not 💖

okay so before we even get into it — this page lives in the POSIX Programmer's Manual (the 3POSIX corner of the world, not the Linux one). Real talk though: the Linux implementation of this interface may differ from what's written here, so if you're on Linux you should go peek at the corresponding Linux manual page for the actual tea. And also... it might just not be implemented on Linux at all. 🫠 So, like, vibe check first, always.

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✨ PROLOG ✨

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

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🌸 NAME 🌸

isatty — test for a terminal device

🎀 SYNOPSIS 🎀

#include <unistd.h>

int isatty(int fildes);

🦋 DESCRIPTION 🦋

So the isatty() function is basically asking one very specific question: is fildes — an open file descriptor — associated with a terminal device or not? That's it. That's the whole job. It shall test whether fildes, an open file descriptor, is associated with a terminal device. 💅

⭐ RETURN VALUE ⭐

Here's the glow-up moment:

• isatty() shall return 1 if fildes is associated with a terminal. slay.
• Otherwise, it shall return 0 and may set errno to indicate the error. (may. not guaranteed. don't come for me.)

💀 ERRORS 💀

The isatty() function may fail if:

• EBADF — the fildes argument is not a valid open file descriptor. bestie that's not even a real fd 😭
• ENOTTY — the file associated with the fildes argument is not a terminal. correct, it's giving "not a terminal" energy.

The following sections are informative.

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🌈 EXAMPLES 🌈

None. (yeah. nothing. iconically empty. 👑)

💜 APPLICATION USAGE 💜

⚠️ Important caveat, no cap: isatty() does not necessarily indicate that a human being is available for interaction via fildes. It is quite possible that non-terminal devices are connected to the communications line.

so like... a terminal device ≠ an actual person on the other end. the vibes can be deceiving. 🙈

🍓 RATIONALE 🍓

None.

🧚 FUTURE DIRECTIONS 🧚

None.

🔥 SEE ALSO 🔥

• The Base Definitions volume of POSIX.1‐2017, <unistd.h>

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💖 COPYRIGHT 💖

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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and that's the whole page, bestie 🫶 this absolute classic was brought to you by IEEE/The Open Group, dated 2017, filed under ISATTY(3POSIX) — go check whether your fd is a terminal, you got this 💅✨