isatty(3) — Linux manual page

isatty(3)                Library Functions Manual               isatty(3)

NAME         top

       isatty - test whether a file descriptor refers to a terminal

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <unistd.h>

       int isatty(int fd);

DESCRIPTION         top

       The isatty() function tests whether fd is an open file descriptor
       referring to a terminal.

RETURN VALUE         top

       isatty() returns 1 if fd is an open file descriptor referring to a
       terminal; otherwise 0 is returned, and errno is set to indicate
       the error.

ERRORS         top

       EBADF  fd is not a valid file descriptor.

       ENOTTY fd refers to a file other than a terminal.  On some older
              kernels, some types of files resulted in the error EINVAL
              in this case (which is a violation of POSIX, which
              specifies the error ENOTTY).

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       attributes(7).
       ┌──────────────────────────────────────┬───────────────┬─────────┐
       │ Interface                            │ Attribute     │ Value   │
       ├──────────────────────────────────────┼───────────────┼─────────┤
       │ isatty()                             │ Thread safety │ MT-Safe │
       └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS         top

       POSIX.1-2008.

HISTORY         top

       POSIX.1-2001, SVr4, 4.3BSD.

SEE ALSO         top

       fstat(2), ttyname(3)

COLOPHON         top

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Linux man-pages 6.15            2025-05-17                      isatty(3)

Pages that refer to this page: bash(1),  ttyname(3)

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