Perl, Why is @INC different?

Question

I have a simple Perl script that prints out @INC as the following:

#!/usr/bin/perl
print $_, "\n" for @INC;

I execute the script in 2 different ways with ./test.pl and perl test.pl, the output as the following:

[neevek@~/bin]$ ./test.pl 
/Library/Perl/5.12/darwin-thread-multi-2level
/Library/Perl/5.12
/Network/Library/Perl/5.12/darwin-thread-multi-2level
/Network/Library/Perl/5.12
/Library/Perl/Updates/5.12.3
/System/Library/Perl/5.12/darwin-thread-multi-2level
/System/Library/Perl/5.12
/System/Library/Perl/Extras/5.12/darwin-thread-multi-2level
/System/Library/Perl/Extras/5.12
.   
[neevek@~/bin]$ perl test.pl 
/opt/local/lib/perl5/site_perl/5.12.3/darwin-multi-2level
/opt/local/lib/perl5/site_perl/5.12.3
/opt/local/lib/perl5/vendor_perl/5.12.3/darwin-multi-2level
/opt/local/lib/perl5/vendor_perl/5.12.3
/opt/local/lib/perl5/5.12.3/darwin-multi-2level
/opt/local/lib/perl5/5.12.3
/opt/local/lib/perl5/site_perl
/opt/local/lib/perl5/vendor_perl
.   

My question is: what's behind the scenes for executing a perl script with ./script.pl and perl script.pl? what causes the script to output different @INC?

Answer 1

The script is executing perl from /usr/bin through the shebang line, but launching the script from the command line uses a different perl binary, from /opt/somewhere (see which perl for the path). You can use #!/usr/bin/env perl to make both options behave the same.

Answer 2

You have two perl installations on your system.

When you execute ./test.pl, it's /usr/bin/perl that is chosen, as written on the first line of your script.

When you execute perl test.pl, it's the first perl found in the PATH environment variable that is chosen. Type which perl to discover where it is.