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Re^2: Pipes: Why does this fail?

by cmv (Chaplain)
on Aug 26, 2010 at 14:31 UTC ( #857469=note: print w/ replies, xml ) Need Help??


in reply to Re: Pipes: Why does this fail?
in thread Pipes: Why does this fail?

JavaFan++

Thanks for the quick help. I've modified the test script (see below) and it now works as expected.

One question though. Using the tail -f line below causes the script to fail, reverting to the cat line makes it work. I don't understand why?

Thanks

-Craig

use strict; use warnings; use FileHandle; # Create named pipe... my $pipe = "/tmp/mypipe"; system("ksh -c 'if [ ! -p $pipe ]; then mkfifo $pipe; fi'"); # Setup input process... open(IN, '|-', "cat - > $pipe") || die "Can't open IN process: $!"; IN->autoflush(1); # Setup output process... #open(OUT, '-|', "tail -f $pipe") || die "Can't open out process: $!"; open(OUT, '-|', "cat $pipe") || die "Can't open out process: $!"; OUT->autoflush(1); my $i=0; print STDERR "Sending input...\n"; print IN "This is message $i\n"; # Read output... print "Reading...\n"; my $line; while($line = <OUT>) { $i++; print $line; print IN "This is message $i\n"; sleep 1; }


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Re^3: Pipes: Why does this fail?
by JavaFan (Canon) on Aug 26, 2010 at 15:35 UTC
    My guess would be that 'tail -f' first tries to seek to the end - but a named pipe isn't seekable. Why it doesn't die, I do not know.

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