Perl operator: $|++; dollar sign pipe plus plus

Question

I\'m working on a new version of an already released code of perl, and found the line:

$|++;

AFAIK, $| is related with pipes, as explained

Answer 1

It's an old idiom, from the days before IO::Handle. In modern code this should be written as

use IO::Handle; STDOUT->autoflush(1);

Answer 2

$| is an abbreviation for $OUTPUT_AUTOFLUSH, as you had found out. The ++ increments this variable.

$| = 1 would be the clean way to do this (IMHO).

Answer 3

It increments autoflush, which is most probably equivalent to turning it on.

Answer 4

$| defaults to 0; doing $|++ thus increments it to 1. Setting it to nonzero enables autoflush on the currently-selected file handle, which is STDOUT by default, and is rarely changed.

So the effect is to ensure that print statements and the like output immediately. This is useful if you're outputting to a socket or the like.