mpapet has asked for the wisdom of the Perl Monks concerning the following question:

I'm working on a qpsmtpd/Dovecot programming task to expand my knowledge. I want to deliver mail using Dovecot's LDA. The shell command that works looks like this: 
/usr/lib/dovecot/deliver -f test@somedomain.com -d test@mailtask.dom <
+ demo.mail

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Order is important. The email file goes on the end. Question 1: What are other more convoluted ways of writing that command? I tried to pipe and it just didn't work. It should be obvious my STDIN-foo is weak. So... very... weak... My test code that doesn't work looks like this: 
use strict;

open FH, "< ./demo.mail";
my @all = <FH>;
close FH;

my $stringified = '';
foreach (@all) {
  $stringified .= $_;
  }

#print $stringified;

close STDOUT;
my $test = open (STDOUT, ' $stringified | /usr/lib/dovecot/deliver -f 
+test\@somedomain.com -d test\@mailtask.dom ');
print $test;

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Question 2: how do I write the open line to work like the command line version?

Replies are listed 'Best First'.
Re: Newbie: Pipe/STDIN Clarification
by mrstlee (Beadle) on Nov 05, 2011 at 11:41 UTC
    You don't need to touch STDOUT actually, and you can simplify the file read:
    my $stringified = '';
{
#Go into local slurp mode ..
local $/=undef;
open FH, "< ./demo.mail";
$stringified = <FH>;
close FH;


open (CMD_OUT, "/usr/lib/dovecot/deliver -f 
+test\@somedomain.com -d test\@mailtask.dom $stringified"|);
my $test = <CMD_OUT>;
print $test;
close CMD_OUT;
}

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    The 'local $/=undef' bit turns off the normal record separator (newline by default). So when the filehandle is read the data is slurped in as one record. The point of enclosing in {}'s is to localise the effect - outside the {}'s the default separator will be used.

    You could also use the back-tick notation to run the shell command: 
    my $test = `/usr/lib/dovecot/deliver -f 
+test\@somedomain.com -d test\@mailtask.dom $stringified`;

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    There are other ways of course. This is perl after all.
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[d/l]
[select]
      Two problems: (1) your "local slurp" isn't local enough, and (2) I think you misread the OP's intention -- mpapet wants to write to the "deliver" process, not read from it. (And BTW, you should indent, and be careful about how line-wrapping in code blocks is handled here at PM.) 
      my $stringified;
{
    local $/;  # defaults to undef
    open my $fh, '<', './demo.mail';  # 3-arg open is nice
    $stringified = <$fh>;
}
# input's done, end-of-block closes the file and reverts to normal i/o

my @cmd = qw(
     /usr/lib/dovecot/deliver
     -f test@somedomain.com
     -d test@mailtask.dom );

open( CMD_OUT, '|-', @cmd ) or die $!;
print CMD_OUT $stringified;
close CMD_OUT;

      [download]
      (Updated to use lexically-scoped file handle in the localized input block -- that's what will cause the file to be closed on leaving the block.)
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[d/l]
        Ah - but as you say I misread the OP's intention. The localised slurp also encompassed the (incorrectly) assumed read from the command - which I assumed would come with line feeds.

        Thanks for the tip on indents.
[reply]
      Thanks for both replies.

      If I try to pass the contents of the variable, it errors out. "Fatal: Unknown argument: From" That's the first line of my demo.mail file. I think it's safe to assume it is reading the string as a file name only.

      That means one more step of writing the email out to disk using the lda program as-is.

[reply]
        It's unfortunate that the first two replies to your OP (from Anonymous Monk and mrstlee) were wrong, and/or didn't quite get your question. Of course there's no guarantee that my replies are correct, either...
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Re: Newbie: Pipe/STDIN Clarification
by Anonymous Monk on Nov 05, 2011 at 05:16 UTC
    See perlintro/perlopentut, basically 
    open my($out), 'command |' or die $!;
print $out $_ while <$in>;
close $out;

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    Using system can be ok :) system "command < file";

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[d/l]
[select]
      That open statement has things the wrong way around. To open a file handle for printing to a pipeline command, it goes like this: 
      open my $fh, '| command' or die $!;

      [download]
      Or better yet, use the 3-arg open call -- and while we're at it, let's provide the command as an array, and get the process-ID: 
      my @command = qw/downstream_process -a option1 -b option2 -etc/;

my pid = open( my $fh, '|-', @command ) or die $!;

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      (The form of open call shown by AnonyMonk would be for running a command so that you can read its output, and you wouldn't write to that file handle.)
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[d/l]
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Re: Newbie: Pipe/STDIN Clarification
by mrstlee (Beadle) on Nov 05, 2011 at 13:31 UTC
    And while I think of it there are neater ways to join arrays of strings:
    #Works for all perl versions
join '', @string_arr; #Obviously you can use any string as the first a
+rg of join e.g. "\n"

#Since 5.10(I think?Maybe 5.8)
open STRING_HNDL, ">", \(my $str);
print STRING_HNDL @string_arr;
close STRING_HNDL;
#$str now contains the strings in @string_arr concatenated together

print "@string_arr"; # A space is put in between successive elements o
+f @string_arr

    [download]
    Have fun!
[reply]
[d/l]

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