Asynchronous processes and anonymous handles

yaralian has asked for the wisdom of the Perl Monks concerning the following question:

Hi, I am trying to run a separate asynchronous process from a perl script. I use a handle and rather than open a file run a piped command. This works fine. But if it's inside a loop at the second iteration of the loop the handle being the same the command doesn't run. To get around this I decide to use anonymous handles but nothing seems to work. Anyone know what I'm doing wrong?

# This is oversimplified but should work.
# The $command string is generated each time
# The $handle is supposed to be an anon file handle.

use IO::File;

    for($f=0; $f<10; $f++){
        my $handle = IO::File -> new();
        open($handle, "$command |");   
    }
[download]

Help please!!! Thanks in advance John

Comment on Asynchronous processes and anonymous handles Download Code

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Re: Asynchronous processes and anonymous handles by moritz (Cardinal) on May 16, 2008 at 07:12 UTC
`$handle` goes out of scope after each iteration, thus an implicit close is called. If you want to actually use your file handles you have to store them somewhere.	[reply] [d/l]
Re: Asynchronous processes and anonymous handles by waba (Monk) on May 16, 2008 at 19:06 UTC
I'll add that assigning a new `IO::File` to `$handle` before calling open probably doesn't do what you'd expect: If FILEHANDLE is an undefined scalar variable (or array or hash element) the variable is assigned a reference to a new anonymous filehandle, otherwise if FILEHANDLE is an expression, its value is used as the name of the real filehandle wanted. (This is considered a symbolic reference, so "use strict ’refs’" should not be in effect.) So a declared `$handle` is all you need. It can even be written as `open my $handle, "$command \|"`. Combining with moritz's advice, `my @handles; foreach my $f ( 0 .. 9 ) { open $handles[$f], "$command \|"; }` [download] Of course, this is assuming that you actually want to read the standard output of `$command`. If all you want to do is fire and forget the process, there are lighter alternatives (system).	[reply] [d/l] [select]