perl, version 5.005_03 built for sun4-solari

That explains it. Your ancient SunOS system is using an ancient Perl release. The code I posted requires Perl 5.8 or later, due to its use of the "3-argument" form of the open call, which wasn't available in perl 5.5 (which is what you have in this case). Sorry, I just assumed that no one would still be using such an old version of Perl.

To fix that, use the "2-argument" form for the open call -- like this:

#!/usr/bin/perl

use strict;
use warnings;

my @cmd_list = ( 'echo 1', 'echo 2', 'echo 3', 'echo 4' );

$|++;  # turn off buffering

my $shpid = open( my $sh, '|/bin/bash' )
    or die "Can't open a shell process: $!\n";

for my $cmd ( @cmd_list ) {
    print $sh "$cmd\n";
}
print $sh "exit\n";
close $sh;
waitpid( $shpid, 0 );

print "Shell's all done.  Moving right along...\n";
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That approach will also work with more recent versions of perl.