Yaah as the monks said its absolutly true. But as a brief to explain about it in detail .....

When you send output to a file using print or write, the operating system might not write it right away. Some systems first send the output to a special array known as a buffer; when the buffer becomes full, it is written all at once. This process of output buffering is usually a more efficient way to write data.

In some circumstances, you might want to send output straight to your output file without using an intervening buffer. (For example, two processes might be sending output to the standard output file at the same time.) The $| system variable indicates whether a particular file is buffered. By default, the Perl interpreter defines a buffer for each output file, and $| is set to 0. To eliminate buffering for a particular file, select the file and then set the $| variable to a nonzero value. For example, the following code eliminates buffering for the MYFILE output file:

        select ("MYFILE");
        $| = 1;
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These statements set MYFILE as the default output file and then turn off buffering for it.