Perl provides several mechanisms for warning the user about potential problems with the program. The use warnings pragma turns on a default set of warnings for the Perl runtime to produce should it detect questionable code. The -w command-line argument serves the same purpose. It is considered so useful that the perl(1) manpage [Wall 2011] dryly notes the first bug in Perl is that :
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"the -w switch is not mandatory" [Wall 2011] .
The use warnings pragma must be used in all Perl code.
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|---|---|---|---|---|
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use warnings;
use strict;
my %days = ("Sunday" => 'pray',
"Monday" => 'work',
"Tuesday" => 'work',
"Wednesday" => 'work',
"Thursday" => 'work',
"Friday" => 'work',
"Saturday" => 'rest');
sub what_to_do {
my $day = shift;
if ($days{$day} eq 'work') {
return 'work hard';
}
if (exists $days{$day}) {
return $days{$day};
} else {
return "do nothing";
}
}
my $task = what_to_do('tomorrow');
print "Prepare to $task\n";
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This code produces the following output:
| Code Block |
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Use of uninitialized value within %days in string eq at ./example.pl line 16. Prepare to do nothing |
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| Code Block | ||||
|---|---|---|---|---|
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use warnings; use strict; no strict 'refs'; our $sunday = 'pray'; # ... |
This code produces the following output:
| Code Block |
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Prepare to do nothing |
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This compliant solution suppresses the strictness checking to as minimal a scope as possible. Because the strict strictness checking is suppressed only inside the what_to_do subroutine, other regions of the code can still be checked for strict compliance.
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Recommendation | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
MSC02-PL | lowLow | unlikelyUnlikely | mediumMedium | P2 | L2 |
Related Guidelines
CERT C Secure Coding Standard: MSC00-C. Compile cleanly at high warning levels
CERT C++ Secure Coding Standard: MSC00-CPP. Compile cleanly at high warning levels
L3 |
Automated Detection
Tool | Diagnostic |
|---|---|
Perl::Critic | TestingAndDebugging::ProhibitNoStrict |
Perl::Critic | TestingAndDebugging:;ProhibitNoWarnings |
Perl::Critic | TestingAndDebugging::ProhibitProlongedStrictureOverride |
Perl::Critic | TestingAndDebugging::RequireUseStrict |
Related Guidelines
| SEI CERT C Coding Standard | MSC00-C. Compile cleanly at high warning levels |
|---|---|
| SEI CERT C++ Coding Standard | VOID MSC00-CPP. Compile cleanly at high warning levels |
Bibliography
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| 2005] | "Overriding Strictures," p |
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EXP30-PL. Do not use deprecated or obsolete functions 02. Expressions