fcntl filehandle, function, arg
Calls the file control function (with the function-specific arg)
to use on the file
or device opened with filehandle. fcntl
calls Unix's fcntl function (not available
on Win32 platforms). If the function is not implemented,
the program exits with a fatal error. fcntl sets
file descriptors for a filehandle. This built-in command is usable when you use the
Fcntl module in the standard distribution:
This module imports the correct function definitions. See the description of the Fcntl module in Chapter 8, Standard Modules.use Fcntl;
The return value of fcntl (and ioctl) is as follows:
| System call returns | Perl returns |
|---|---|
-1 | Undefined value |
0 | String "0 but true" |
| Anything else | That number |
Thus Perl returns true on success and false on failure, yet you can still easily determine the actual value returned by the operating system.