There are three buffering states:

• unbuffered
• block buffered: Writes when 4KB* is accumulated.
• line buffered: Writes when \n is encountered or 4KB* is accumulated.

If a handle is buffered, line buffering is always and only used when the file handle is connected to a terminal.

So, if you're writing to a file, \n won't flush. But if you're writing to STDOUT and it hasn't been redirected, \n will flush if buffering wasn't turned off.

You can turn on buffering using

use IO::Handle qw( );
FH->autoflush(0);
[download]

You can turn off buffering using

use IO::Handle qw( );
FH->autoflush(1);
[download]

You can flush manually using

use IO::Handle qw( );
FH->flush();
[download]

* — Well, I *think* the buffer size is 4KB.