gensym (in Symbol) returns a ref to a new glob every time it's called. 

my $cmdin=gensym;
my $cmdout=gensym;
my $cmderr=gensym;
open3($cmdin, $cmdout, $cmderr, $cmd);

[download]

is like 

my $cmdin=gensym;
my $cmdout=gensym;
my $cmderr=gensym;
open3(\*IN, \*OUT, \*ERR, $cmd);

[download]

without the risk of conflicting names.

In reply to Re^2: Best practice for sychronous output handling using open3()? by ikegami
in thread Best practice for sychronous output handling using open3()? by OfficeLinebacker

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