I was looking for a way to read the output of an external command piping its output to a script in a non-blocking way. I read that using Fcntl's fcntl() can be used to add the O_NONBLOCK flag to the file handle and wonder whether that is a safe practice when that filehandle came from opening an external command and reading its output using: open(my $fh, '-|', 'ls -al'); This is an example:

use Fcntl qw(F_GETFL F_SETFL O_NONBLOCK);    

my $pid = open my $fh, '-|', 'sleep 3; echo aaaa' // die $!; 

my $flags = fcntl($fh, F_GETFL, 0) or die "failed to get flags, $!";  
+    
fcntl($fh, F_SETFL, $flags | O_NONBLOCK) or die "Couldn't set file fla
+gs: $!\n";
my $output = <$fh>;
if( defined $output ){
        print "got output: '$output'\n"    
} else { print "no output right now.\n" }

print "now waiting to end ...\n";
#waitpid $pid, 0;
close($fh); 
#kill 'TERM', $pid;
print "end.\n";

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I wanted to turn the above into a CUFP but I am not sure what are the caveats wrt Perl and OS. Anyone knows if any?

bw, bliako

In reply to non-blocking IO from open("-|")ing an external program with fcntl by bliako

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