There are times you create a perl program that writes to STDOUT or a log file and you do not want the printing buffered. By default perl will buffer your output. This can have unexpected results when you are calling print within a loop, or you are expected data written to your logs instantly.

Luckily perl has ways to shut off the buffering of the output. There is a special variable to turn off buffering of STDOUT and you can set autoflush on you File Handles. Here is an example program that shows how you would do each.

#!/usr/bin/perl

############################################################
# Example program to show how to set STDOUT and FILES to
# NOT buffer and print immediately
#
############################################################
use FileHandle;

# to make STDOUT flush immediately, simply set the variable
# this can be useful if you are writing to STDOUT in a loop
# many times the buffering will cause unexpected output results
$| = 1;

# to prevent buffering when writing to files, set autoflush on
# the file handle
open (OUT, ">>test.out") || die "could not create test.out - $!";
OUT->autoflush(1);

print OUT "writing to file\n";

close(OUT)

exit(0);

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