---
name: "isatty"
section: "3p"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/isatty/3p"
---

# isatty(3p)

test for a terminal device

## 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.

## NAME

isatty — test for a terminal device

## SYNOPSIS

```
#include <unistd.h>
```

int isatty(int *fildes*);

## DESCRIPTION

The *isatty*() function shall test whether *fildes*, an open file descriptor, is associated with a terminal device.

## RETURN VALUE

The *isatty*() function shall return 1 if *fildes* is associated with a terminal; otherwise, it shall return 0 and may set *errno* to indicate the error.

## ERRORS

The *isatty*() function may fail if:

- **EBADF**

  The *fildes* argument is not a valid open file descriptor.

- **ENOTTY**

  The file associated with the *fildes* argument is not a terminal.

*The following sections are informative.*

## EXAMPLES

None.

## APPLICATION USAGE

The *isatty*() function 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.

## RATIONALE

None.

## FUTURE DIRECTIONS

None.

## SEE ALSO

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

## 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 .