#! perl -slw
use strict;

my $pseudo = '[h2]Test[/h2] [h3]Test[/h3]';

# Create a hash of codes for substitution
my %directSubs = (
         qr/\[h(\d)\]/  => '"<h$1>"',
         qr/\[\/h(\d)\]/=> '"</h$1>"'
         );

# Substitute the codes
while(($a,$b) = each %directSubs){
 $pseudo =~ s/$a/$b/giee;
}

print $pseudo;

__END__
# Output
C:\test>215723
<h2>Test</h2> <h3>Test</h3>

C:\test>