Fastest way to get input from a filehandle

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

Replies are listed 'Best First'.
Re: Fastest way to get input from a filehandle by sauoq (Abbot) on Oct 29, 2005 at 13:51 UTC
They should all be similar enough that it shouldn't matter. Note in particular: `$ perl -MO=Deparse -e '$line = readline(*STDIN)' $line = <STDIN>; -e syntax OK` [download] If you are really concerned about it, you should be using `read()` or `sysread()` instead. -sauoq "My two cents aren't worth a dime.";	[reply] [d/l] [select]
Re: Fastest way to get input from a filehandle by japhy (Canon) on Oct 29, 2005 at 15:15 UTC
I would expect the fourth one is the slowest, since you're going out of your way to get a line. The first three are, I believe, identical. But this is not where you should be looking for speed increases in your code. This is such a minor issue. You're over-optimizing. Jeff `japhy` Pinyan, P.L., P.M., P.O.D, X.S.: Perl, regex, and `perl` hacker How can we ever be the sold short or the cheated, we who for every service have long ago been overpaid? ~~ Meister Eckhart	[reply]
Re^2: Fastest way to get input from a filehandle by sauoq (Abbot) on Oct 29, 2005 at 16:34 UTC
I would think the 2nd would be slowest since there is an extra step of getting the right filehandle from the string... `$ perl -MO=Deparse -e 'readline(STDIN)' readline 'STDIN'; -e syntax OK` [download] Not sure when that happens though. (One time penalty?) I would expect the fourth to be about as quick as the others (after the open) as it's just dup'ing STDIN. Is it slower to store a filehandle in a lexical? (I wouldn't think so but have no real clue.) shrug Not that any of this changes the fact that it shouldn't matter to the OP. :-) -sauoq "My two cents aren't worth a dime.";	[reply] [d/l]
Re: Fastest way to get input from a filehandle by bageler (Hermit) on Oct 29, 2005 at 15:59 UTC
find out for yourself, using a static file, the Benchmark module and the exported timethese() subroutine. There are many examples of its usage on this site.	[reply]
Re: Fastest way to get input from a filehandle by pg (Canon) on Oct 29, 2005 at 16:28 UTC
To be frank, the way you read does not make any difference in this context. In this case, the time taking a human being to response and type is much longer than the read takes.	[reply]
Re^2: Fastest way to get input from a filehandle by graff (Chancellor) on Oct 29, 2005 at 18:34 UTC
Of course, if the question is being asked in the context of reading STDIN from a pipe (rather than from a keyboard), then there could be a good reason to figure out whether one method of reading is faster or slower than another, and a benchmark test would be worthwhile -- even if all it does is prove that there's hardly any difference. And in that regard, the Benchmark module probably isn't necessary or even appropriate; the unix "time" command would probably do. Just put together a suitable test script that reads and processes data from STDIN, but accepts a command-line option to determine what sort of syntax to use for reading, then run a series of commands like: `feeder_process \| time test-perl-reader diamond > /dev/null # (repeat several times, average the results) feeder_process \| time test-perl-reader readline1 > /dev/null # (repeat, average the results) feeder_process \| time test-perl-reader readline2 > /dev/null # (you know the drill...)` [download] If the difference among the various averages is greater than the variance among test runs for any single method, then maybe there's a real difference in the efficiency of the different input methods. But I would expect any differences to be a very small fraction of the overall pipeline time.	[reply] [d/l]


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