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Re^2: Different perl behavior between V5.10 and V5.14

by markseger (Beadle)
on Apr 01, 2013 at 12:39 UTC ( #1026476=note: print w/ replies, xml ) Need Help??


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

Since what it currently happening is the code is reading the new record, printing it and then immediately exiting the loop, I inserted an eof() before trying to read the pipe from the pipe and did verify eof() is returning a 1. So I put in some code to call eof() before trying to read and if it returns 1 to simply do a read I know will fail and then follow it with next to stay in the inner loop.

Seems to work just fine but it doesn't make me happy. Perhaps this might offer a clue to someone else who does know what's going on?

-mark


Comment on Re^2: Different perl behavior between V5.10 and V5.14
Re^3: Different perl behavior between V5.10 and V5.14
by vsespb (Hermit) on Apr 01, 2013 at 12:54 UTC
    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.
      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.

      -mark

        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"; }

        -mark

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