#!/usr/bin/perl
use strict;
use warnings;
use feature qw{ say };

open OUT, '>', 'log.txt' or die $!;
print OUT "bla\n";

open IN, '<', 'log.txt' or die $!;
my $nothing = <IN>;
say "Read: $nothing.\n";

close OUT;
my $bla = <IN>;
say "Read: $bla.\n";
[download]

so yes, autoflush is not default, but you don't need to close after explicitly setting it

#!/usr/bin/perl
use strict;
use warnings;
use feature qw{ say };

unlink "./log.txt" or warn "$!";         # in case


open OUT, '>>', 'log.txt' or die $!;

{
    my $previous_default = select(OUT);  # save previous default
    $|++;                                # autoflush OUT
    select($previous_default);           # restore previous default
}

print OUT "before close";

open IN, '<', 'log.txt' or die $!;

my $read;

$read = <IN>;
chomp $read;
say "Before close: <$read>";

close OUT;
[download]

Before close: <before close>

Cheers Rolf
_{(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery}

even easier is using method autoflush directly.

Got it from HaukeX' recent post.

I should have read the FAQ: https://perldoc.perl.org/perlfaq5#How-do-I-flush/unbuffer-an-output-filehandle?-Why-must-I-do-this? more carefully :)

#!/usr/bin/perl
use strict;
use warnings;
use feature qw{ say };

unlink "./log.txt" or warn "$!";



open OUT, '>>', 'log.txt' or die $!;



if (0){                                 # as you like
    my $previous_default = select(OUT); # save previous default
    $|++;                               # autoflush OUT
    select($previous_default);          # restore previous default
} else {
    #use PerlIO;                         # needed for Perl <5.14
    OUT->autoflush();
}


print OUT "before close";

open IN, '<', 'log.txt' or die $!;

my $read;

$read = <IN>;
chomp $read;
say "Before close: <$read>";

close OUT;
[download]

-*- mode: compilation; default-directory: "d:/tmp/pm/" -*-
Compilation started at Fri Feb 12 02:23:56

C:/Perl_524/bin\perl.exe -w d:/tmp/pm/auto_flush.pl 
Before close: <before close>

Compilation finished at Fri Feb 12 02:23:56
[download]

Cheers Rolf
_{(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery}

> Not sure about the debugger, but code shows otherwise:

It's not the debugger, I think the system command (aka backticks) is causing a flush

#!/usr/bin/perl
use strict;
use warnings;
use feature qw{ say };

unlink "./log.txt" or warn "$!";


open OUT, '>>', 'log.txt' or die $!;
print OUT "before system\n";

print `type log.txt`;

print OUT "after system\n";

open IN, '<', 'log.txt' or die $!;
my $nothing = <IN>;
say "Before close: $nothing.\n";


close OUT;
my $bla = <IN>;
say "After close: $bla.\n";
[download]

-*- mode: compilation; default-directory: "d:/tmp/pm/" -*-
Compilation started at Thu Feb 11 19:29:04

C:/Perl_524/bin\perl.exe -w d:/tmp/pm/auto_flush.pl 
before system
Before close: before system
.

After close: after system
.


Compilation finished at Thu Feb 11 19:29:05
[download]

Cheers Rolf
_{(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery}