ISATTY(1) fish-shell ISATTY(1)

# [NAME](#NAME)

isatty - test if a file descriptor is a terminal

# [SYNOPSIS](#SYNOPSIS)

```
isatty [FILE_DESCRIPTOR]
```

# [DESCRIPTION](#DESCRIPTION)

**isatty** tests if a file descriptor is a terminal (as opposed to a file). The name is derived from the system call of the same name, which for historical reasons refers to a teletypewriter (TTY).

**FILE DESCRIPTOR** may be either the number of a file descriptor, or one of the strings **stdin**, **stdout**, or **stderr**. If not specified, zero is assumed.

If the specified file descriptor is a terminal device, the exit status of the command is zero. Otherwise, the exit status is non-zero. No messages are printed to standard error.

The **-h** or **--help** option displays help about using this command.

# [EXAMPLES](#EXAMPLES)

From an interactive shell, the commands below exit with a return value of zero:

```
isatty
isatty stdout
isatty 2
echo | isatty 1
```

And these will exit non-zero:

```
echo | isatty
isatty 9
isatty stdout > file
isatty 2 2> file
```

# [Copyright](#Copyright)

fish-shell developers

October 12, 2026 4.9

---

Document: isatty(1) from fish 4.9.3-r2 (Chainguard OS)
Source: https://github.com/fish-shell/fish-shell