Enable Perl strict mode to restrict unsafe constructs
In Perl, you can enforce using the strict mode to reduce the chance of nasty error, e.g.
$foo = 'bar'; print $foo;
If you run the above problem, it is completely valid.
# perl test.pl bar
However, if you use the strict pragma
use strict; $foo = 'bar'; print $foo;
And run the program again..
# perl test.pl Global symbol "$foo" requires explicit package name at test.pl line 3. Global symbol "$foo" requires explicit package name at test.pl line 4. Execution of test.pl aborted due to compilation errors.
Since the $foo is not declared before the first use, so the compilation stopped. In modern Perl developements, it is recommended to alwasys use the strict pragma in order to write a better and maintainable program.
To fix the problem, you need to use the my keyword, e.g.
use strict; my $foo = 'bar'; print $foo;
And run the program again. (Thanks Jeroen for the suggestion)