I am trying to execute a system command. The problem is that 1) there is a space in the directory name for the directory path, and 2) there is a pipe and a redirection.

(2) means you are trying to execute a shell command, but you aren't running a shell. When using the single-argument form of system, Perl will invoke the command in a shell if it thinks necessary. But you aren't using the single-argument form of system.

system("mysqldump","--add-drop-table","-uroot","-ppassword", "mydataba
+se","|","gzip","-9c",">","$backup_dir/mydatabase.sql.gz");
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is the same as

mysqldump '-add-drop-table' '-uroot '-ppassword' 'mydatabase' '|' 'gzi
+p' '-9c' '>' "$backup_dir/mydatabase.sql.gz"
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at the prompt.

You have a couple of options.

• Perl is the shell, so have Perl do the redirection.

  use IPC::Open3 qw( open3 );
  
  {
     local *FROM_MYSQLDUMP;
     open(local *INPUT,  '<', '/dev/null') or die $!;
     open(local *OUTPUT, '>', "$backup_dir/mydatabase.sql.gz") or die $!
  +;
  
     my $mysqldump_pid = open3('<&INPUT', \*FROM_MYSQLDUMP, '>&STDERR',
        mysqldump => (
           '--add-drop-table',
           '-u'.'root',
           '-p'.'password',
           'mydatabase',
        ),
     );
  
     my $gzip_pid = eval {
        open3('<&FROM_MYSQLDUMP', '>&OUTPUT', '>&STDERR',
           gzip => ( '-9c' ),
        )
     };   
  
     if (!$gzip_pid) {
        my $e = $@;
        kill(KILL => $mysqldump_pid);
        waitpid($mysqldump_pid, 0);
        die($e);
     }
     
     waitpid($mysqldump_pid, 0);
     waitpid($gzip_pid, 0);
  }
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• You could craft a shell command and have the shell do the piping.

  sub text_to_shell_lit(_) {
     return $_[0] if $_[0] =~ /^[a-zA-Z0-9_\-]+\z/;
     my $s = $_[0];
     $s =~ s/'/'\\''/g;
     return "'$s'";
  }
  
  my $mysqldump_cmd = join ' ', map text_to_shell_lit,
     mysqldump => (
        '--add-drop-table',
        '-u'.'root',
        '-p'.'password',
        'mydatabase',
     );
  
  my $gzip_cmd = join ' ', map text_to_shell_lit,
     gzip => ( '-9c' );
     
  my $output_file_lit = text_to_shell_lit("$backup_dir/mydatabase.sql.gz
  +");
     
  system("$mysqldump_cmd | $gzip_cmd > $output_file_lit");
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You could surely simplify at the cost of overhead.

• IPC::Run and IPC::Run3 allows you to have a callback. You could use the callback as a pipe.

• Again with IPC::Run and IPC::Run3, you could get the entire response from one process into memory and pass it to the next in the chain.

• You could also replace gzip with a Perl module, leaving you with just external process. Then, all you'd need is backticks.