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\section isatty isatty - test if a file or file descriptor is a tty.
\subsection isatty-synopsis Synopsis
<tt>isatty [FILE | DEVICE | FILE DESCRIPTOR NUMBER]</tt>
\subsection isatty-description Description
<tt>isatty</tt> tests if a file or file descriptor is a tty.
The argument may be in the form of a file path, device, or file descriptor
number. Without an argument, <tt>standard input</tt> is implied.
If the resolved file descriptor is a tty, the command returns zero. Otherwise, the command exits one. No messages are printed to standard error.
\subsection isatty-examples Examples
From an interactive shell, the commands below exit with a return value of zero:
<pre>
isatty
isatty stdout
isatty 2
echo | isatty /dev/fd/1
</pre>
And these will exit non-zero:
<pre>
echo | isatty
isatty /dev/fd/9
isatty stdout > file
isatty 2 2> file
</pre>
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