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mysterious error of read function in solaris

by david2008 (Scribe)
on Jan 19, 2012 at 13:30 UTC ( #948778=perlquestion: print w/ replies, xml ) Need Help??
david2008 has asked for the wisdom of the Perl Monks concerning the following question:

Hi all, I have the following script
use strict; use warnings; my ($output_file) = 'a.exe'; open INPUT, $output_file or die "Cannot read the installer fil +e $output_file: $!"; binmode INPUT; my $content = ""; my $buffer; while ( read (INPUT, $buffer, 65536) # read in (up to) 64k +chunks, write ) { if ($!){die $!} $content.=$buffer; }; die "Cannot read the installer file $output_file: $!" if $! && + ($! ne 'Bad file descriptor'); close INPUT; return $content;
When i run it on linux it works, but on solaris i get an error message in the read command.
Bad file number at line 13.<br>
What can be the reason? Thanks, David

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Re: mysterious error of read function in solaris
by Anonymous Monk on Jan 19, 2012 at 13:55 UTC

    Only check $! right after a system call

    open ... or die $!;
    close ... or die $!;
    print ... or die $!;
    my $read = read ...;
    die $! unless defined $read;
Re: mysterious error of read function in solaris
by JavaFan (Canon) on Jan 19, 2012 at 14:27 UTC
    You're dying whenever $! is a non-false value. But $! having a non-false value is not an indication anything is wrong. Check the system call, only if that is false, $! will have a useful value. In all other cases, you may not rely on $! having a sensible value.

    In this, my bet is that Solaris sets errno to 13 during one of the system calls that are being made. And an OS is free to do so, the 13 only needs to signal something if the call fails (which it won't, because if the read fails, you aren't testing $!).

      Which variable should i check if read fails?
        Whatever variable you put the return value of read in. From perldoc -f read
        Returns the number of characters actually read, 0 at end of file, or undef if there was an error (in the latter case $! is also set).
        So, you'd do something like:
        my $r; while ($r = read ...) { ... do stuff here ... } die "read failed: $!" unless defined $r;
        I guess since 5.10, you could also write:
        while (read(...) // die "read failed: $!") { ... do stuff here ... }
        but I don't think I would want to recommend that.

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