What does this do?

[Bob]

$|++;

I see that in code but my searches have come up with nothing.

Robert

 

[Eugene Mikheyev]

$|++;

I see that in code but my searches have come up with nothing.

As $| is a boolean variable, I suspect the one who wrote this thought
incrementing is faster than assigning, i.e. when $x is 0, $x++ is faster
than $x = 1. Maybe I am wrong, this is just an assumption.

 

[gnari]

$|++;

I see that in code but my searches have come up with nothing.

$| is explained in
perldoc perlvar

the ++ is just a cute way to set it to a true value. if assumes
the value is not -1

gnari

 

[Peter J. Acklam]

$|++;

I see that in code but my searches have come up with nothing.

perldoc perlvar

It is a slightly obscure way of disable output buffering. The
recommended way is

$| = 1;

Peter

 

[Sherm Pendley]

$|++;

I see that in code but my searches have come up with nothing.

If it helps, the default value of $| is undef, or zero in numeric context,
so incrementing it with ++ makes it non-zero. The results of assigning a
non-zero value to $| are documented in 'perldoc perlvar'.

sherm--

 

[Brad Baxter]

$| is explained in
perldoc perlvar

the ++ is just a cute way to set it to a true value. if assumes
the value is not -1

gnari

The value is NEVER -1.

Regards,

Brad

 

[Peter J. Acklam]

There's no advantage of writing '$| ++' instead of '$| = 1', but
the latter is far less obscure.

And the latter turns on buffering also in the extremely unlikely
event that $| should ever be -1, in which case $|++ would turn it
off.

Peter

 

[Jeff 'japhy' Pinyan]

And the latter turns on buffering also in the extremely unlikely
event that $| should ever be -1, in which case $|++ would turn it
off.

Except that $| can't ever be -1 (unless you've done *| = \-1, in which
case $|++ will throw a "Modification of read-only" error).

$|, as defined by the internal magic supporting it, is set to 0 when given
a false value, and 1 when given ANY true value.

--
Jeff "japhy" Pinyan % How can we ever be the sold short or
RPI Acacia Brother #734 % the cheated, we who for every service
RPI Corporation Secretary % have long ago been overpaid?
http://japhy.perlmonk.org/ %
http://www.perlmonks.org/ % -- Meister Eckhart

 

[Sam Holden]

And the latter turns on buffering also in the extremely unlikely
event that $| should ever be -1, in which case $|++ would turn it
off.

$| is a special variable it can never have the value of -1 and hence that
event is not possible at all.

It is either 0 or 1.

perl -le "$|=-1;print $|"

 

[gnari]

$|, as defined by the internal magic supporting it, is set to 0 when given
a false value, and 1 when given ANY true value.

in that case the $|++ does not even have the advantage
of allowing us to 'localize' the value as in:

# unknown $| state
$|++;
... do stuff ...
$|--;
this will alway end by resetting $| to 0, even if it
was originally 1

on the other hand $|-- will always reverse the value.
now I will have to find a use for that ...

gnari

 

[Ala Qumsieh]

on the other hand $|-- will always reverse the value.
now I will have to find a use for that ...

Some refer to this as the flip-flop behaviour. It is an invaluable tool
for perlgolf. You can use it to alternate between two array elements in
a loop without the need for an explicit variable. Here are a couple of
perlgolf "holes" with solutions using this behaviour:

http://perlgolf.sourceforge.net/TPR/0/3/
http://perlgolf.sourceforge.net/TPR/0/5a/

--Ala

 

[Peter J. Acklam]

Except that $| can't ever be -1 (unless you've done *| = \-1, in
which case $|++ will throw a "Modification of read-only" error).

Darn, then someone has fooled me. What I wrote above is virtually
a citation of something I read somewhere. No big deal, though,
but now I wonder where I got it from.

Peter

 

[Jeff 'japhy' Pinyan]

in that case the $|++ does not even have the advantage
of allowing us to 'localize' the value as in:

# unknown $| state
$|++;
... do stuff ...
$|--;
this will alway end by resetting $| to 0, even if it
was originally 1

Luckily we have 'local' which does exactly what you want.

# unknown $| state
{
local $| = 1;
# ...
}
# $| is restored here

--
Jeff "japhy" Pinyan % How can we ever be the sold short or
RPI Acacia Brother #734 % the cheated, we who for every service
RPI Corporation Secretary % have long ago been overpaid?
http://japhy.perlmonk.org/ %
http://www.perlmonks.org/ % -- Meister Eckhart