MD013 - Line length

Tags: line_length

Aliases: line-length Parameters: linelength, codeblocks, tables (number; default 80, boolean; default true)

This rule is triggered when there are lines that are longer than the configured line length (default: 80 characters). To fix this, split the line up into multiple lines.

This rule has an exception where there is no whitespace beyond the configured line length. This allows you to still include items such as long URLs without being forced to break them in the middle.

You also have the option to exclude this rule for code blocks and tables. To do this, set the code_blocks and/or tables parameters to false.

Code blocks are included in this rule by default since it is often a requirement for document readability, and tentatively compatible with code rules. Still, some languages do not lend themselves to short lines.

MD004 - Unordered list style

Tags: bullet, ul

Aliases: ul-style

Parameters: style ("consistent", "asterisk", "plus", "dash"; default "consistent")

This rule is triggered when the symbols used in the document for unordered list items do not match the configured unordered list style:

* Item 1
+ Item 2
- Item 3

To fix this issue, use the configured style for list items throughout the document:

* Item 1
* Item 2
* Item 3

Note: the configured list style can be a specific symbol to use (asterisk, plus, dash), or simply require that the usage be consistent within the document.

MD026 - Trailing punctuation in header

Tags: headers

Aliases: no-trailing-punctuation

Parameters: punctuation (string; default ".,;:!?")

This rule is triggered on any header that has a punctuation character as the last character in the line:

# This is a header.

To fix this, remove any trailing punctuation:

# This is a header

Note: The punctuation parameter can be used to specify what characters class as punctuation at the end of the header. For example, you can set it to '.,;:!' to allow headers with question marks in them, such as might be used in an FAQ.

MD030 - Spaces after list markers

Tags: ol, ul, whitespace

Aliases: list-marker-space

Parameters: ulsingle, olsingle, ulmulti, olmulti (number, default 1)

This rule checks for the number of spaces between a list marker (e.g. '-', '*', '+' or '1.') and the text of the list item.

The number of spaces checked for depends on the document style in use, but the default is 1 space after any list marker:

* Foo
* Bar
* Baz

1. Foo
1. Bar
1. Baz

1. Foo
   * Bar
1. Baz

A document style may change the number of spaces after unordered list items and ordered list items independently, as well as based on whether the content of every item in the list consists of a single paragraph, or multiple paragraphs (including sub-lists and code blocks).

For example, the style guide at http://www.cirosantilli.com/markdown-styleguide/#spaces-after-marker specifies that 1 space after the list marker should be used if every item in the list fits within a single paragraph, but to use 2 or 3 spaces (for ordered and unordered lists respectively) if there are multiple paragraphs of content inside the list:

* Foo
* Bar
* Baz

vs.

*   Foo

    Second paragraph

*   Bar

or

1.  Foo

    Second paragraph

1.  Bar

To fix this, ensure the correct number of spaces are used after list marker for your selected document style.

MD030 - Spaces after list markers

Tags: ol, ul, whitespace

Aliases: list-marker-space

Parameters: ulsingle, olsingle, ulmulti, olmulti (number, default 1)

This rule checks for the number of spaces between a list marker (e.g. '-', '*', '+' or '1.') and the text of the list item.

The number of spaces checked for depends on the document style in use, but the default is 1 space after any list marker:

* Foo
* Bar
* Baz

1. Foo
1. Bar
1. Baz

1. Foo
   * Bar
1. Baz

A document style may change the number of spaces after unordered list items and ordered list items independently, as well as based on whether the content of every item in the list consists of a single paragraph, or multiple paragraphs (including sub-lists and code blocks).

For example, the style guide at http://www.cirosantilli.com/markdown-styleguide/#spaces-after-marker specifies that 1 space after the list marker should be used if every item in the list fits within a single paragraph, but to use 2 or 3 spaces (for ordered and unordered lists respectively) if there are multiple paragraphs of content inside the list:

* Foo
* Bar
* Baz

vs.

*   Foo

    Second paragraph

*   Bar

or

1.  Foo

    Second paragraph

1.  Bar

To fix this, ensure the correct number of spaces are used after list marker for your selected document style.

MD026 - Trailing punctuation in header

Tags: headers

Aliases: no-trailing-punctuation

Parameters: punctuation (string; default ".,;:!?")

This rule is triggered on any header that has a punctuation character as the last character in the line:

# This is a header.

To fix this, remove any trailing punctuation:

# This is a header

Note: The punctuation parameter can be used to specify what characters class as punctuation at the end of the header. For example, you can set it to '.,;:!' to allow headers with question marks in them, such as might be used in an FAQ.

For more information visit Source: http://eslint.org/docs/rules/

Disallow this keywords outside of classes or class-like objects. (no-invalid-this)

Under the strict mode, this keywords outside of classes or class-like objects might be undefined and raise a TypeError.

Rule Details

This rule aims to flag usage of this keywords outside of classes or class-like objects.

Basically this rule checks whether or not a function which are containing this keywords is a constructor or a method.

This rule judges from following conditions whether or not the function is a constructor:

• The name of the function starts with uppercase.
• The function is assigned to a variable which starts with an uppercase letter.
• The function is a constructor of ES2015 Classes.

This rule judges from following conditions whether or not the function is a method:

• The function is on an object literal.
• The function is assigned to a property.
• The function is a method/getter/setter of ES2015 Classes. (excepts static methods)

And this rule allows this keywords in functions below:

• The call/apply/bind method of the function is called directly.
• The function is a callback of array methods (such as .forEach()) if thisArg is given.
• The function has @this tag in its JSDoc comment.

Otherwise are considered problems.

This rule applies only in strict mode. With "parserOptions": { "sourceType": "module" } in the ESLint configuration, your code is in strict mode even without a "use strict" directive.

Examples of incorrect code for this rule in strict mode:

/*eslint no-invalid-this: "error"*/
/*eslint-env es6*/

"use strict";

this.a = 0;
baz(() => this);

(function() {
    this.a = 0;
    baz(() => this);
})();

function foo() {
    this.a = 0;
    baz(() => this);
}

var foo = function() {
    this.a = 0;
    baz(() => this);
};

foo(function() {
    this.a = 0;
    baz(() => this);
});

obj.foo = () => {
    // `this` of arrow functions is the outer scope's.
    this.a = 0;
};

var obj = {
    aaa: function() {
        return function foo() {
            // There is in a method `aaa`, but `foo` is not a method.
            this.a = 0;
            baz(() => this);
        };
    }
};

foo.forEach(function() {
    this.a = 0;
    baz(() => this);
});

Examples of correct code for this rule in strict mode:

/*eslint no-invalid-this: "error"*/
/*eslint-env es6*/

"use strict";

function Foo() {
    // OK, this is in a legacy style constructor.
    this.a = 0;
    baz(() => this);
}

class Foo {
    constructor() {
        // OK, this is in a constructor.
        this.a = 0;
        baz(() => this);
    }
}

var obj = {
    foo: function foo() {
        // OK, this is in a method (this function is on object literal).
        this.a = 0;
    }
};

var obj = {
    foo() {
        // OK, this is in a method (this function is on object literal).
        this.a = 0;
    }
};

var obj = {
    get foo() {
        // OK, this is in a method (this function is on object literal).
        return this.a;
    }
};

var obj = Object.create(null, {
    foo: {value: function foo() {
        // OK, this is in a method (this function is on object literal).
        this.a = 0;
    }}
});

Object.defineProperty(obj, "foo", {
    value: function foo() {
        // OK, this is in a method (this function is on object literal).
        this.a = 0;
    }
});

Object.defineProperties(obj, {
    foo: {value: function foo() {
        // OK, this is in a method (this function is on object literal).
        this.a = 0;
    }}
});

function Foo() {
    this.foo = function foo() {
        // OK, this is in a method (this function assigns to a property).
        this.a = 0;
        baz(() => this);
    };
}

obj.foo = function foo() {
    // OK, this is in a method (this function assigns to a property).
    this.a = 0;
};

Foo.prototype.foo = function foo() {
    // OK, this is in a method (this function assigns to a property).
    this.a = 0;
};

class Foo {
    foo() {
        // OK, this is in a method.
        this.a = 0;
        baz(() => this);
    }

    static foo() {
        // OK, this is in a method (static methods also have valid this).
        this.a = 0;
        baz(() => this);
    }
}

var foo = (function foo() {
    // OK, the `bind` method of this function is called directly.
    this.a = 0;
}).bind(obj);

foo.forEach(function() {
    // OK, `thisArg` of `.forEach()` is given.
    this.a = 0;
    baz(() => this);
}, thisArg);

/** @this Foo */
function foo() {
    // OK, this function has a `@this` tag in its JSDoc comment.
    this.a = 0;
}

When Not To Use It

If you don't want to be notified about usage of this keyword outside of classes or class-like objects, you can safely disable this rule. Source: http://eslint.org/docs/rules/

Use $(STATEMENT) instead of legacy `STATEMENT`

Problematic code

echo "Current time: `date`"

Correct code

echo "Current time: $(date)"

Rationale

Backtick command substitution `STATEMENT` is legacy syntax with several issues.

1. It has a series of undefined behaviors related to quoting in POSIX.
2. It imposes a custom escaping mode with surprising results.
3. It's exceptionally hard to nest.

$(STATEMENT) command substitution has none of these problems, and is therefore strongly encouraged.

Exceptions

None.

See also

• http://mywiki.wooledge.org/BashFAQ/082

Notice

Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.

echo won't expand escape sequences. Consider printf.

Problematic code:

echo "Name:\t$value"

Correct code:

printf "Name:\t%s\n" "$value"

Rationale:

Backslash escapes like \t and \n are not expanded by echo, and become literal backslash-t, backslash-n.

printf does expand these sequences, and should be used instead.

Other, non-portable methods include echo -e '\t' and echo $'\t'. ShellCheck will warn if this is used in a script with shebang #!/bin/sh.

If you actually wanted a literal backslash-t, use

echo "\\t"

Exceptions

None

Notice

Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.

MD013 - Line length

Tags: line_length

Aliases: line-length Parameters: linelength, codeblocks, tables (number; default 80, boolean; default true)

This rule is triggered when there are lines that are longer than the configured line length (default: 80 characters). To fix this, split the line up into multiple lines.

This rule has an exception where there is no whitespace beyond the configured line length. This allows you to still include items such as long URLs without being forced to break them in the middle.

You also have the option to exclude this rule for code blocks and tables. To do this, set the code_blocks and/or tables parameters to false.

Code blocks are included in this rule by default since it is often a requirement for document readability, and tentatively compatible with code rules. Still, some languages do not lend themselves to short lines.

Quote this to prevent word splitting

Problematic code:

ls -l $(getfilename)

Correct code:

# getfilename outputs 1 file
ls -l "$(getfilename)"

# getfilename outputs multiple files, linefeed separated
getfilename | while IFS='' read -r line
do
  ls -l "$line"
done

Rationale:

When command expansions are unquoted, word splitting and globbing will occur. This often manifests itself by breaking when filenames contain spaces.

Trying to fix it by adding quotes or escapes to the data will not work. Instead, quote the command substitution itself.

If the command substitution outputs multiple pieces of data, use a loop instead.

Exceptions

In rare cases you actually want word splitting, such as in

gcc $(pkg-config --libs openssl) client.c

This is because pkg-config outputs -lssl -lcrypto, which you want to break up by spaces into -lssl and -lcrypto. An alternative is to put the variables to an array and expand it:

args=( $(pkg-config --libs openssl) )
gcc "${args[@]}" client.c

The power of using an array becomes evident when you want to combine, for example, the command result with user-provided arguments:

compile () {
    args=( $(pkg-config --libs openssl) "${@}" )
    gcc "${args[@]}" client.c
}
compile -DDEBUG
+ gcc -lssl -lcrypto -DDEBUG client.c

Notice

Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.

MD004 - Unordered list style

Tags: bullet, ul

Aliases: ul-style

Parameters: style ("consistent", "asterisk", "plus", "dash"; default "consistent")

This rule is triggered when the symbols used in the document for unordered list items do not match the configured unordered list style:

* Item 1
+ Item 2
- Item 3

To fix this issue, use the configured style for list items throughout the document:

* Item 1
* Item 2
* Item 3

Note: the configured list style can be a specific symbol to use (asterisk, plus, dash), or simply require that the usage be consistent within the document.

MD004 - Unordered list style

Tags: bullet, ul

Aliases: ul-style

Parameters: style ("consistent", "asterisk", "plus", "dash"; default "consistent")

This rule is triggered when the symbols used in the document for unordered list items do not match the configured unordered list style:

* Item 1
+ Item 2
- Item 3

To fix this issue, use the configured style for list items throughout the document:

* Item 1
* Item 2
* Item 3

Note: the configured list style can be a specific symbol to use (asterisk, plus, dash), or simply require that the usage be consistent within the document.

MD004 - Unordered list style

Tags: bullet, ul

Aliases: ul-style

Parameters: style ("consistent", "asterisk", "plus", "dash"; default "consistent")

This rule is triggered when the symbols used in the document for unordered list items do not match the configured unordered list style:

* Item 1
+ Item 2
- Item 3

To fix this issue, use the configured style for list items throughout the document:

* Item 1
* Item 2
* Item 3

Note: the configured list style can be a specific symbol to use (asterisk, plus, dash), or simply require that the usage be consistent within the document.

MD013 - Line length

Tags: line_length

Aliases: line-length Parameters: linelength, codeblocks, tables (number; default 80, boolean; default true)

This rule is triggered when there are lines that are longer than the configured line length (default: 80 characters). To fix this, split the line up into multiple lines.

This rule has an exception where there is no whitespace beyond the configured line length. This allows you to still include items such as long URLs without being forced to break them in the middle.

You also have the option to exclude this rule for code blocks and tables. To do this, set the code_blocks and/or tables parameters to false.

Code blocks are included in this rule by default since it is often a requirement for document readability, and tentatively compatible with code rules. Still, some languages do not lend themselves to short lines.

MD013 - Line length

Tags: line_length

Aliases: line-length Parameters: linelength, codeblocks, tables (number; default 80, boolean; default true)

This rule is triggered when there are lines that are longer than the configured line length (default: 80 characters). To fix this, split the line up into multiple lines.

This rule has an exception where there is no whitespace beyond the configured line length. This allows you to still include items such as long URLs without being forced to break them in the middle.

You also have the option to exclude this rule for code blocks and tables. To do this, set the code_blocks and/or tables parameters to false.

Code blocks are included in this rule by default since it is often a requirement for document readability, and tentatively compatible with code rules. Still, some languages do not lend themselves to short lines.

MD013 - Line length

Tags: line_length

Aliases: line-length Parameters: linelength, codeblocks, tables (number; default 80, boolean; default true)

This rule is triggered when there are lines that are longer than the configured line length (default: 80 characters). To fix this, split the line up into multiple lines.

This rule has an exception where there is no whitespace beyond the configured line length. This allows you to still include items such as long URLs without being forced to break them in the middle.

You also have the option to exclude this rule for code blocks and tables. To do this, set the code_blocks and/or tables parameters to false.

Code blocks are included in this rule by default since it is often a requirement for document readability, and tentatively compatible with code rules. Still, some languages do not lend themselves to short lines.

MD002 - First header should be a top level header

Tags: headers

Aliases: first-header-h1

Parameters: level (number; default 1)

This rule is triggered when the first header in the document isn't a h1 header:

## This isn't a H1 header

### Another header

The first header in the document should be a h1 header:

# Start with a H1 header

## Then use a H2 for subsections

MD013 - Line length

Tags: line_length

Aliases: line-length Parameters: linelength, codeblocks, tables (number; default 80, boolean; default true)

This rule is triggered when there are lines that are longer than the configured line length (default: 80 characters). To fix this, split the line up into multiple lines.

This rule has an exception where there is no whitespace beyond the configured line length. This allows you to still include items such as long URLs without being forced to break them in the middle.

You also have the option to exclude this rule for code blocks and tables. To do this, set the code_blocks and/or tables parameters to false.

Code blocks are included in this rule by default since it is often a requirement for document readability, and tentatively compatible with code rules. Still, some languages do not lend themselves to short lines.