>set PERLIO=stdio

>perl a.pl
===============dry run============
        printing [perl_output_newline]
***perl_output_newline
        calling  [c_output_newline]
###c_output_newline
        printing [perl_output]
***perl_output  calling  [c_output]
###c_output
=============test_global==========
        printing [perl_output_newline]
        calling  [c_output_newline]
        printing [perl_output]
        calling  [c_output]
test_global buffer:
(***perl_output_newline\n###c_output_newline\n***perl_output###c_output)


>set PERLIO=perlio

>perl a.pl
===============dry run============
        printing [perl_output_newline]
***perl_output_newline
        calling  [c_output_newline]
###c_output_newline
        printing [perl_output]
        calling  [c_output]
***perl_output###c_output
=============test_global==========
        printing [perl_output_newline]
        calling  [c_output_newline]
        printing [perl_output]
        calling  [c_output]
test_global buffer:
(***perl_output_newline\n###c_output_newline\n***perl_output###c_output)