ISATTY(1)

okay bestie, welcome to the ISATTY(1) page from fish-shell — yes, the manual name is literally fish-shell, and today’s main character is isatty. let’s get into it 💅✨

✨ NAME ✨

isatty — test if a file descriptor is a terminal 🎀

🎀 SYNOPSIS 🎀

isatty [FILE_DESCRIPTOR]

💅 DESCRIPTION 💅

okay so 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 — and for historical reasons, that call refers to a teletypewriter (TTY). history really said “vibes only” 😭

The FILE DESCRIPTOR may be either the number of a file descriptor, or one of the strings stdin, stdout, or stderr. If it’s not specified, zero is assumed. no cap.

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. silence is golden, fr fr 🤫

• -h, --help — displays help about using this command. cute and helpful 🫶

🦋 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 💖

fish-shell developers

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this iconic page was brought to you by fish-shell version 4.9, dated Sep 08, 2026 — ISATTY(1) out, byeee bestie 💅🌈✨