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Re^3: Different perl behavior between V5.10 and V5.14

by vsespb (Chaplain)
on Apr 01, 2013 at 12:54 UTC ( #1026480=note: print w/replies, xml ) Need Help??

in reply to Re^2: Different perl behavior between V5.10 and V5.14
in thread Different perl behavior between V5.10 and V5.14

Hm. Weird. I've modified code like this:
#!/usr/bin/perl -w use Time::HiRes; $SIG{"ALRM"}=\&sigAlarm; my $interval=1; my $uInterval=$interval*10**6; Time::HiRes::ualarm($uInterval, $uInterval); open TAIL, "tail -f xyz|" or die 'couldnt open xyz'; while (1) { while ($line=<TAIL>) { $X = $!; print $line; } if (eof(TAIL)) { print "EOF TAIL!\n"; } print "Fell through... $!\n"; } sub sigAlarm { print "alarm\n"; }
After first EOF found, it never works normal again. It just prints EOF TAIL + Fell through... in infinite loop. So, I think filehandle never recovered after Perl finds EOF.

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Re^4: Different perl behavior between V5.10 and V5.14
by markseger (Beadle) on Apr 01, 2013 at 13:29 UTC
    I think the problem is once you've done the first $line=<TAIL> it's too late. Here's what I wrote that DOES work correctly and will not exit the loop, but as I said I'm not proud of it ;):

    #!/usr/bin/perl -w use Time::HiRes; $SIG{"ALRM"}=\&sigAlarm; my $interval=1; my $uInterval=$interval*10**6; Time::HiRes::ualarm($uInterval, $uInterval); my $logname='xyz'; open TAIL, "tail -f $logname|" or die "couldn't open $logname"; while (1) { while(1) { if (eof(TAIL)) { printf "EOF: %d\n", eof(TAIL); $line=<TAIL>; next; } last if !($line=<TAIL>); print $line; } print "Fell through...\n"; } sub sigAlarm { print "alarm\n"; }

    I also wonder if doing that eof() test at the beginning go throw me into an infinite loop under some conditions, but as so far this seems to be ok for now.


      I think I finally have a clean solution. After much reading and asking around in the office someone helped me with this snippet, assuming TAIL is the file handle you're doing the tail -f on. The answer is to simply redo the failed operation which previous responses had suggested. So if anyone is interested this is what I've settled on and particularly like it because it's short and straightforward:

      while (1) { while(1) { my $line = <TAIL>; if (!defined($line)) { redo if $! eq 'Interrupted system call'; last; } print $line; } printf "Fell through...\n"; }


        Yep, looks like a good workaround. Also I belive you can use
        instead of
        $! eq 'Interrupted system call'
        (as per '%!' in perlvar)

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[stevieb]: ...on request. There's some supporting work I need to do, as well as update the docs, but it's in the v1.12 branch if anyone wants to play with it...
[stevieb]: ...issue 62 will track what else needs to be done.

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