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| .TH ISATTY 3 2021-03-22 "Linux" "Linux Programmer's Manual" |
| .SH NAME |
| isatty \- test whether a file descriptor refers to a terminal |
| .SH SYNOPSIS |
| .nf |
| .B #include <unistd.h> |
| .PP |
| .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). |
| .ad l |
| .nh |
| .TS |
| allbox; |
| lbx lb lb |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR isatty () |
| T} Thread safety MT-Safe |
| .TE |
| .hy |
| .ad |
| .sp 1 |
| .SH CONFORMING TO |
| POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD. |
| .SH SEE ALSO |
| .BR fstat (2), |
| .BR ttyname (3) |
