The usual way is to close STDIN in the process which doesn't need it.
Do you really need 2 diferent STDIN ?

anyway, to play with filehandle use TYPEGLOB:

$variable=*FILEHANDLE;
print $variable "things to be printed\n";
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or open with the mode '&' (from the cookbook)

open(OLD_OUT,">&STDOUT");       #save curent STDOUT to OLD_OUT
open(STDOUT,">/tmp/file.out"); #reassign STDOUT to /tmp/file.out
close STDOUT ;
open(STDOUT,">&OLD_OUT");      #restore the previous STDOUT
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Or use local as gloom suggested.