Out of curiosity, what does phrasing it in that way buy you?

I thought maybe you were gaining an advantage from the short circuit of && so I wrote a benchmark, but the times came back so close together that the difference is easily attributed to background processes. So I ran the deparser and found that perl converts this to an if(){} structure, which is (as you said) easier to read.

E:\Projects>perl -MO=Deparse -we "my $s; $_ && do { $s = $_ }"
my $s;
if ($_) {
    $s = $_;
}
-e syntax OK
[download]

My guilty admission is that I just like the way it looks better.

• It would seem that somehow the whole log line is getting matched by the (^,+) part of the regex because that's what's getting substituted back in.

Just in case this isn't clear yet, it isn't that the mentioned part of the regex is matching the whole line, it is that the regex is failing and no substitution is taking place

It does no good to have an unanchored .* at both ends.

This looks like one of the regex optimizer bugs. You should post it to comp.lang.perl.moderated or submit it with perlbug.

I'd write this:

if(  $_ =~ / to=([^,]+), /  ) {
    $to_addr = $1;
} else {
    warn "Unmatched to= in line: $_";
}
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It does no good to have an unanchored .* at both ends. but it does because regexps are greedy (by default). If they weren't there, the substitution would do nothing, it would just put $1 back where it found it. But the .* cause the whole line to be matched, and thus *only* the $1 is put back in. that said it is no doubt safer to anchor such a regex

Sorry, you are right.

I think I was thinking ahead to the change I made to just match against the line and just assign $1 to the variable. Mea culpa.

I ran your regex over my sendmail logs and it behaved pretty much as expected. The only lines it missed were emails directed at multiple recipients, like so:

Jul 19 02:43:29 zoom1 sendmail[26193]: CAA26174: to=<XXX@aol.com>,<YYY@aol.com>,<ZZZ@aol.com>, ctladdr=<XXX@TelePath.Com> (13408/40), delay=00:01:14, xdelay=00:00:01, mailer=esmtp, relay=zd.mx.aol.com. [152.163.224.101], stat=Sent (OK)

Modifying the regex a bit cleared that up and I didn't get any more anomalous behavior. Here's the test code I used:

#!/usr/bin/perl

while (<STDIN>)
{
        # Only match lines that have a " to=" in them.
        # The leading space is important because many
        # lines have a "proto="
        if (/ to=/)
        {
                #($to_addr = $_) =~ s/.* to=([^,]+), .*/$1/;
                ($to_addr = $_) =~ s/.* to=(.+?), .*/$1/;
                print "$to_addr";
        }
}
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-Matt

What version of perl are you running? We are a little
behind the curve (5.004) and I suspect that may be the
reason.

-Mark

5.005_02

-Matt

$to_addr = $1 if /.+? to=([^,]+), .*/;
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($to_addr)=$_=~/......
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open FH, "mylog" etc....
while (<FH>)
{
    do these steps
}
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$to_addr = ($_ =~ rest of stuff);
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$to_addr = ($_ =~ rest of stuff);

That will set $to_addr to either 1 or 0 depending on whether the substitution succeeded or not.

-Matt