I created a files called test.ps.

$ cat test.ps 
%!PS
/Courier findfont
20 scalefont
setfont
72 500 moveto
(Hello world!) show
showpage
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So here is a recreation of the script that is failing.

#!/opt/csw/bin/perl -w

use strict;
use warnings;

my $prolog = <<ENDPROLOG;
%!PS
/Courier findfont
20 scalefont
setfont
72 500 moveto
(Hello world!) show
showpage
ENDPROLOG
my $PRINT_CMD = '/usr/bin/lp -o nobanner';
open my $output, '|-', $PRINT_CMD
    or die "Can't open pipe to $PRINT_CMD: $!";
print $output $prolog;
close $output or warn "Error while closing pipe to $PRINT_CMD: $!";
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