writing to a file using print

Brad.Walker has asked for the wisdom of the Perl Monks concerning the following question:

I am attempting to write to a file use the print keyword. I'm doing the following:

     print $test_file $random_data
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$random_data is a 1MB string and $test_file is the file handle that was opened up using the 3 argument version of open.

The problem that I'm encountering is the Perl interpreter is breaking this large write into 4K writes at the system call level. I don't really want this because I'm trying to do some NFS performance measurements and the breakup of writes is causing me problems. I know that I could use syswrite, but was hoping to stay away from this.

Thanks.
-brad w.

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Re: writing to a file using print by ikegami (Patriarch) on Feb 13, 2007 at 04:53 UTC
Do you get the same problem with `syswrite`? It doesn't use the buffering system used by `print`. It might still not work, though, because `syswrite` is not guaranteed to write everything it is asked to write (in a single call). `my $written = syswrite($test_file, $buf, length($buf)); die("Unable to write to file: $!\n") if not defined $written; die("Unable to write whole string in one call\n") if $written != length($buf);` [download] For comparison, `syswrite` is normally used as follows: `my $offset = 0; my $to_write = length($buf); while ($to_write > 0) { my $written = syswrite($test_file, $buf, $to_write, $offset); die("Unable to write to file: $!\n") if not defined $written; $to_write -= $written; $offset += $written; }` [download]	[reply] [d/l] [select]
Re: writing to a file using print by dorko (Prior) on Feb 13, 2007 at 04:40 UTC
Brad, Looks like you're "suffering from buffering". Try turning buffering off by adding the following line before your print statement: `$\|++;` [download] Cheers, Brent -- Yeah, I'm a Delt.	[reply] [d/l]
Re^2: writing to a file using print by geekphilosopher (Friar) on Feb 13, 2007 at 06:50 UTC
Or, if you want to follow the lead of The Damian in Perl Best Practices, you can do: `$\| = 1;` [download]	[reply] [d/l]
Re^3: writing to a file using print by dorko (Prior) on Feb 13, 2007 at 15:35 UTC
This whole discussion gives me nasty flashbacks to a time when I couldn't have been more wrong. At that point I switched from `$\| = 1;` to `$\|++;`. I've mostly gotten over it... :) Cheers, Brent -- Yeah, I'm a Delt.	[reply] [d/l] [select]