Linux checks whether the standard output is redirected.

Code: 1.C

# Include <unistd. h>

# Include <stdio. h>

# Include <stdlib. h>

Int main ()

{

If (! Isatty (fileno (stdout )))

{

Fprintf (stderr, "You are not a terminal \ n ");

Exit (1 );

}

Exit (0 );

}

GCC 1.C-o t

./T

 

./T> file output you are not a terminal

Analysis: isatty checks whether stdout of the standard output stream is connected to the terminal. isatty's parameter is the file descriptor, while stdout is the file stream,

Therefore, fileno (stdout) is used to obtain the file descriptor.

If the stdout of the standard output stream is not connected to the terminal, the standard output is redirected.