NAME

B::Lint - Perl lint

SYNOPSIS

perl -MO=Lint[,OPTIONS] foo.pl

DESCRIPTION

The B::Lint module is equivalent to an extended version of the -w option of perl. It is named after the program lint which carries out a similar process for C programs.

OPTIONS AND LINT CHECKS

Option words are separated by commas (not whitespace) and follow the usual conventions of compiler backend options. Following any options (indicated by a leading -) come lint check arguments. Each such argument (apart from the special all and none options) is a word representing one possible lint check (turning on that check) or is no-foo (turning off that check). Before processing the check arguments, a standard list of checks is turned on. Later options override earlier ones. Available options are:

magic-diamond

Produces a warning whenever the magic <> readline is used. Internally it uses perl's two-argument open which itself treats filenames with special characters specially. This could allow interestingly named files to have unexpected effects when reading.

% touch 'rm *|'
% perl -pe 1

The above creates a file named rm *|. When perl opens it with <> it actually executes the shell program rm *. This makes <> dangerous to use carelessly.

context

Produces a warning whenever an array is used in an implicit scalar context. For example, both of the lines

$foo = length(@bar);
$foo = @bar;

will elicit a warning. Using an explicit scalar() silences the warning. For example,

$foo = scalar(@bar);

implicit-read and implicit-write

These options produce a warning whenever an operation implicitly reads or (respectively) writes to one of Perl's special variables. For example, implicit-read will warn about these:

/foo/;

and implicit-write will warn about these:

s/foo/bar/;

Both implicit-read and implicit-write warn about this:

for (@a) { ... }

bare-subs

This option warns whenever a bareword is implicitly quoted, but is also the name of a subroutine in the current package. Typical mistakes that it will trap are:

use constant foo => 'bar';
@a = ( foo => 1 );
$b{foo} = 2;

Neither of these will do what a naive user would expect.

dollar-underscore

This option warns whenever $_ is used either explicitly anywhere or as the implicit argument of a print statement.

private-names

This option warns on each use of any variable, subroutine or method name that lives in a non-current package but begins with an underscore ("_"). Warnings aren't issued for the special case of the single character name "_" by itself (e.g. $_ and @_).

undefined-subs

This option warns whenever an undefined subroutine is invoked. This option will only catch explicitly invoked subroutines such as foo() and not indirect invocations such as &$subref() or $obj->meth(). Note that some programs or modules delay definition of subs until runtime by means of the AUTOLOAD mechanism.

regexp-variables

This option warns whenever one of the regexp variables $`, $& or $' is used. Any occurrence of any of these variables in your program can slow your whole program down. See perlre for details.

all

Turn all warnings on.

none

Turn all warnings off.

NON LINT-CHECK OPTIONS

-u Package

Normally, Lint only checks the main code of the program together with all subs defined in package main. The -u option lets you include other package names whose subs are then checked by Lint.

EXTENDING LINT

Lint can be extended by with plugins. Lint uses Module::Pluggable to find available plugins. Plugins are expected but not required to inform Lint of which checks they are adding.

The B::Lint->register_plugin( MyPlugin => \@new_checks ) method adds the list of @new_checks to the list of valid checks. If your module wasn't loaded by Module::Pluggable then your class name is added to the list of plugins.

You must create a match( \%checks ) method in your plugin class or one of its parents. It will be called on every op as a regular method call with a hash ref of checks as its parameter.

The class methods B::Lint->file and B::Lint->line contain the current filename and line number.

package Sample;
use B::Lint;
B::Lint->register_plugin( Sample => [ 'good_taste' ] );

sub match {
    my ( $op, $checks_href ) = shift @_;
    if ( $checks_href->{good_taste} ) {
        ...
    }
}

TODO

while(<FH>) stomps $_

strict oo

unchecked system calls

more tests, validate against older perls

BUGS

This is only a very preliminary version.

AUTHOR

Malcolm Beattie, mbeattie@sable.ox.ac.uk.