in reply to Re^2: Speed reading (files)
in thread Speed reading (files)

The advantage of "slurping" is that it works with ttys. I don't think -s does.

Also, is read guaranteed to return the number of bytes requested (if the file is big enough)? sysread isn't.

As an aside, wouldn't read FILE, my $data, $MAX_FILE_SIZE; be faster than using -s, especially on smaller files? I guess you have to find an acceptable $MAX_FILE_SIZE (in Config.pm, maybe???)

By the way, I'm not suprised that read is as fast or faster than "slurping". Why wouldn't it be?

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Re^4: Speed reading (files)
by BrowserUk (Patriarch) on Aug 05, 2005 at 04:30 UTC
    Also, is read guaranteed to return the number of bytes requested (if the file is big enough)? sysread isn't.

    Could you clarify this for me?

    From sysread:

    sysread ... Returns the number of bytes actually read, 0 at end of file, or undef if there was an error ...

    Under what circumstances would sysread fail to return the number of bytes actually requested?

    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?
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[reply]

      Good question. I've heard it many times of the years, but I can't say where. Maybe it's when the handle is not a file handle. FreeBSD's man 2 read supports this theory: "The system guarantees to read the number of bytes requested if the descriptor references a normal file that has that many bytes left before the end-of-file, but in no other case."

      btw, [doc://sysread] works better than [sysread].

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        Great. That clarified things. On a non-file handle, read will wait for more input to become available if the buffer doesn't contain enough to satisfy the request, whereas sysread returns what is available without waiting (subject to EOLs): 

        P:\test>p1
perl> print read STDIN, $in, 10; print "'$in'";;
1234
5678
10
'1234
5678
'

perl> print sysread STDIN, $in, 10; print "'$in'";;
1234
6
'1234
'

        [download]
        Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
        Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?
        "Science is about questioning the status quo. Questioning authority".
        The "good enough" maybe good enough for the now, and perfection maybe unobtainable, but that should not preclude us from striving for perfection, when time, circumstance or desire allow.
[reply]
[d/l]

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