Why does File::Temp use sysopen?

John M. Dlugosz has asked for the wisdom of the Perl Monks concerning the following question:

I found an interesting issue when running under Windows where "normal" text files have CRLF line endings.

Basically, using a generated temporary file from File::Temp was not giving the normal endings, but were "binary" by default.

use File::Temp;
use File::Spec;

print "hello1\n";  # defaults to CRLF, as documented.

open F, ">", "out2.txt";  # ditto.
print F "hello2\n";

open F, "> :utf8", "out3.txt";  # still CRLF
print F "hello3\n";

open F, ">", "out4.txt";
binmode F, ":utf8";  # still OK!
print F "hello4\x{b6}\n";


$h= new File::Temp( TEMPLATE => 'helloXXXXX', SUFFIX => $suffix, UNLIN
+K => 0, DIR => File::Spec->tmpdir());
$fname= $h->filename;
print "sending out5 to $fname\n";
# binmode $h, ":utf8";  # no CR, shows 0x0A only.  But :utf8 silences 
+warning.
print $h "hello5\x{b6}\n";
[download]

Looking at the Perl code for File::Temp, I see that it uses sysopen rather than the normal open. I think that's why it behaves differently.

Why?

And why does sysopen not set up the platform defaults, though it still appears to use IO layers?

—John

Update: behavior on Perl 5.8.4 (ActiveState build 810), but is fixed in Perl 5.8.6 (AS build 811)

Comment on Why does File::Temp use sysopen? Select or Download Code

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Re: Why does File::Temp use sysopen? by revdiablo (Prior) on May 02, 2005 at 17:57 UTC
Why does File::Temp use sysopen? Because sysopen lets you use some useful open flags. Afaik, File::Temp uses this to avoid race conditions that would be created trying to emulate the same behavior with a plain open. Update: Indeed, File::Temp uses the O_EXCL flag by default, which does the following: In many systems the O_EXCL flag is available for opening files in exclusive mode. This is not locking: exclusiveness means here that if the file already exists, sysopen() fails. That way it can keep retrying until it gets a file that didn't exist. Doing this with a `-e` check before using `open` would cause a race condition.	[reply] [d/l] [select]
Re: Why does File::Temp use sysopen? (binmode) by tye (Sage) on May 02, 2005 at 19:19 UTC
You should test your thesis, because using sysopen on Win32 does not cause a file to be in binmode for me ("\n" gets written as "\r\n" when I print "\n" to a such a handle). - tye	[reply]


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