G'day char_perl,

Welcome to the Monastery.

Use the sprintf function to specify the precision you want:

#!/usr/bin/env perl -l

use strict;
use warnings;

my $value = 0.9888;

print '"%.2f" --> ', sprintf '%.2f', $value;
print '"%.4f" --> ', sprintf '%.4f', $value;
print '"%.8f" --> ', sprintf '%.8f', $value;
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Output:

$ pm_1131769_output_precision.pl
"%.2f" --> 0.99
"%.4f" --> 0.9888
"%.8f" --> 0.98880000
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Also note that there is a printf function, but this has a number of gotchas. They're described in the documentation; although, you may just want to follow the advice on the last line:

"Don't fall into the trap of using a printf when a simple print would do. The print is more efficient and less error prone."