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Re^5: Assign Output of Regex to Array (newbie)

by Laurent_R (Canon)
on Oct 01, 2013 at 18:05 UTC ( #1056518=note: print w/replies, xml ) Need Help??

in reply to Re^4: Assign Output of Regex to Array (newbie)
in thread Assign Output of Regex to Array (newbie)

You said in the original post you wanted high performance. Try to replace this:

my @PRC_PRIV = <FILE>; my @PRC_PRIV_ONLY = grep /Run as/ .. /^ /, @PRC_PRIV;

with this:

my @PRC_PRIV_ONLY = grep /Run as/ .. /^ /, <FILE>;

And measure if you get any performance improvement.

Another point is that you may want to include use strict; and use warnings; near the top of your program and declare your variables with the my operator. This is a recommended good practice which will save you a lot of debugging time.

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Re^6: Assign Output of Regex to Array (newbie)
by justsomeguy (Novice) on Oct 01, 2013 at 19:06 UTC

    Thanks! I get about a 1ms improvement doing it that way, using "time" and after serveral iterations testing both ways. Small, but measurable.

    I left off the "use warnings" and "use strict" as well as the variable declarations for this post in interest of brevity. But I always do both.

      Just 1 ms? I thought it would be more. Against a total running time of how long?

      I left off the "use warnings" and "use strict" as well as the variable declarations for this post in interest of brevity. But I always do both.

      Fine, but then, you should rather declare your variables where you use them (in the smallest possible lexical scope), not at the top of your program. For example, you may have something like this:

      foreach my $PRIV(@PRC_PRIV_ONLY) { chomp($PRIV); next if ($PRIV =~ m/Run|^ /); my ($USER, $HOSTN, $CMDN) = split(" ", $PRIV, 3); if (defined($USER)) { print "$PRC_GRP,$USER,$HOSTN,$CMDN \n"; } }

      This way, you are defining truly local variables, and that's a good protection against silly but sometimes nasty bugs. Here above, $PRIV is scoped to the foreach loop, if you use it accidentally somewhere else in the program (which would have no sense), you'll get a compile error telling you that you are doing something wrong with it, and this is much better than having to chase the obscure reason why you don't get the output you expect. Similarly, the $USER, $HOST and $CMDN variables are scoped from the place they are declared to the end of the foreach loop. You'll be told by the compiler if you inadvertently use them where they should not be used.

        The file is only 50K in size. The 1ms improvement is about 15-20%, so scaled up that's considerable.

        Thanks again for the tips on variable scoping. My instinct is to put them all at top and declare globally, but the risks you cite are real.

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[choroba]: You can also try DBD::MariaDB instead of MySQL
[choroba]: it's not on CPAN yet, unfortunately, so you have to install manually from github
[Spenser]: Thanks. I tried DBD::MariaDB just now. It can't find that module.
[Spenser]: oh, I'll check github

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