CODEWITHSUNDEEP
perlexpression
hhh
hhh

Reputation: 2769

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

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 in this link, and I understand this, but I cannot figure out what the ++ (plus plus) means here.

Thank you in advance.

EDIT: Found the answer in this link:

In short: It forces to print (flush) to your console before the next statement, in case the script is too fast.

Sometimes, if you put a print statement inside of a loop that runs really really quickly, you won’t see the output of your print statement until the program terminates. sometimes, you don’t even see the output at all. the solution to this problem is to “flush” the output buffer after each print statement; this can be performed in perl with the following command:

$|++;

[update] as has been pointed out by r. schwartz, i’ve misspoken; the above command causes print to flush the buffer preceding the next output.

Upvotes: 19

Views: 7311

Answers (4)

LeoNerd
LeoNerd

Reputation: 8532

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);

Upvotes: 6

Michael Krelin - hacker
Michael Krelin - hacker

Reputation: 143249

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

Upvotes: 5

Fred Foo
Fred Foo

Reputation: 363787

$| 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).

Upvotes: 16

pndc
pndc

Reputation: 3805

$| 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.

Upvotes: 21

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