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Because Perl programs are typically not explicitly compiled before they are run, they can suffer from typographical errors in variable names. A variable whose name is typed wrongly incorrectly will appear as an undeclared variable to the Perl interpreter , and will therefore contain the undef value , as opposed to the instead of the value of the intended variable.
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Perl's -w command-line option will cause causes a warning to be issued for any variable name in the code that appears exactly once in the code, as this which might indicate a mistyped variable name.
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my $result = compute_number();
print "The result is $reuslt\n"; # oops!
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This causes It causes the program to print the useless output:
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The result is
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and continue execution.
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my $result = compute_number();
print "The result is $result\n";
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