chayashida:

If you don't care what you return, you can simplify it a bit like this:

open(QTREES,$file1) or return print "foo";
[download]

If you do care, then you can use:

open(QTREES,$file1) or (print "foo") && return;
[download]

Example:

$ touch file1; touch file2

$ perl blenge.pl

$ rm file2; perl blenge.pl
Error opening file2: No such file or directory

$ rm file1; perl blenge.pl
Error opening file1: No such file or directory

$ cat blenge.pl 
#!/usr/bin/perl
use strict;

doit();

sub doit {
    open QTREES, 'file1' or return print STDERR "Error opening file1: 
+$!";
    open RTREES, 'file2' or (print STDERR "Error opening file2: $!") &
+& return;
}
[download]

...roboticus

When your only tool is a hammer, all problems look like your thumb.