Update: ikegami++ is right: printf is needed for a more general solution. 
use strict;
use warnings;

my $exp = -4;
my $in  = 5e-2;
my $out = $in/10**$exp;
print "$in --> ${out}e${exp}\n";

__END__
0.05 --> 500e-4

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In reply to Re: Printing with a Specific Scientific Notation Exponent by toolic
in thread Printing with a Specific Scientific Notation Exponent by behindalens

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