system "command1 img.g3 | command2  > img.ps";

##</code><code>##

=> Insecure $ENV{PATH} while running with -T 

##</code><code>##

system "command1 img.g3  > img.pbm";
system "command2 img.pbm  > img.ps";

system "command1", "img.g3"  > img.pbm;