~>cd /var/www/cgi-bin
/var/www/cgi-bin>cat helloworld.pl
#!/usr/bin/perl

print "Content-type: text/html\n\n";
print "Hello World\n";
/var/www/cgi-bin>which perl
/usr/bin/perl
/var/www/cgi-bin>perl helloworld.pl
Content-type: text/html

Hello World
/var/www/cgi-bin>./helloworld.pl
/var/www/cgi-bin>cp helloworld.pl ~
/var/www/cgi-bin>cd 
~>perl helloworld.pl
Content-type: text/html

Hello World
~>./helloworld.pl
Content-type: text/html

Hello World
~>cd /var/www/cgi-bin
/var/www/cgi-bin>cat helloworld2.pl
#!/usr/bin/perl

print "Content-type: text/html\n\n";
print "Hello World2\n";
/var/www/cgi-bin>perl helloworld2.pl
Content-type: text/html

Hello World2
/var/www/cgi-bin>./helloworld2.pl
/var/www/cgi-bin>cp helloworld2.pl ~
/var/www/cgi-bin>cd 
~>perl helloworld2.pl
Content-type: text/html

Hello World2
~>./helloworld2.pl
~>diff helloworld.pl helloworld2.pl
~>

##</code><code>##

EDIT2: ls -l /usr/bin/perl `which perl`
-rwxr-xr-x  2 root root 15660 Mar 13  2006 /usr/bin/perl
-rwxr-xr-x  2 root root 15660 Mar 13  2006 /usr/bin/perl