Detecting error using Perl system() with multiple piped processes

Question

I'm trying to implement a MySQL database restore from a GPG-encrypted file.

The following works perfectly well:

my $status = system(
    "gpg --pinentry-mode loopback --passphrase $passphrase --decrypt $my_encrypted_backup_file"
  . " | "
  . "mysql --host=myhost --user=myuser --password=mysecret mydatabase"
);

assuming no error conditions.

However, if an error condition occurs during the first process (such as an incorrect $passphrase), $status == 0 which erroneously indicates success. I understand this is because the status is returned from the second process, the mysql process.

Is there a generalized way, using system(), to either obtain the status from all the piped-together processes, or to somehow detect an error if any one such process fails?

BTW, I have tested gpg by itself (without its output being piped into mysql) and it does return an error code when an incorrect $passphrase is entered.

A workaround might be some option flag in mysql that returns an error when it receives nothing from gpg. Another workaround is to break up the processes and use a tmp file of some sort. However, I'd love a more generalized solution. Thanks!

Answer 1

If you need fine control like that, don't use the shell.

Calls to mysql can be replaced with using the DBI and DBD::mysql libraries. gpg can be replaced with Crypt::GPG.

If this is not possible, do the piping yourself with open and its |- and -| modes.

open(
    my $gpg_out,
    "-|",
    "gpg --pinentry-mode loopback --passphrase $passphrase --decrypt $my_encrypted_backup_file"
) or die "Can't run gpg: $!";

open(
    my $mysql_in,
    "|-",
    "mysql --host=myhost --user=myuser --password=mysecret mydatabase"
) or die "Can't run mysql: $!";

while(my $line = <$gpg_out>) {
    print $mysql_in $line;
}

close $gpg_out;
close $mysql_in;