'\" t .\" Copyright 2008, Linux Foundation, written by Michael Kerrisk .\" .\" .\" SPDX-License-Identifier: Linux-man-pages-copyleft .\" .TH isatty 3 2024-05-02 "Linux man-pages 6.9.1" .SH NAME isatty \- test whether a file descriptor refers to a terminal .SH LIBRARY Standard C library .RI ( libc ", " \-lc ) .SH SYNOPSIS .nf .B #include .P .BI "int isatty(int " fd ); .fi .SH DESCRIPTION The .BR isatty () function tests whether .I fd is an open file descriptor referring to a terminal. .SH RETURN VALUE .BR isatty () returns 1 if .I fd is an open file descriptor referring to a terminal; otherwise 0 is returned, and .I errno is set to indicate the error. .SH ERRORS .TP .B EBADF .I fd is not a valid file descriptor. .TP .B ENOTTY .I fd refers to a file other than a terminal. On some older kernels, some types of files .\" e.g., FIFOs and pipes on 2.6.32 resulted in the error .B EINVAL in this case (which is a violation of POSIX, which specifies the error .BR ENOTTY ). .SH ATTRIBUTES For an explanation of the terms used in this section, see .BR attributes (7). .TS allbox; lbx lb lb l l l. Interface Attribute Value T{ .na .nh .BR isatty () T} Thread safety MT-Safe .TE .SH STANDARDS POSIX.1-2008. .SH HISTORY POSIX.1-2001, SVr4, 4.3BSD. .SH SEE ALSO .BR fstat (2), .BR ttyname (3)