Template:Str left/doc

This subpage contains documentation, categories, or other content that is not part of the template.
To view the template page itself, see Template:Str left.

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This template is used in system messages.
Changes to it can cause immediate changes to the Wikimedia user interface.
To avoid major disruption, any changes should be tested in the template's /sandbox or /testcases subpages, or in your own user subpage. The tested changes can be added to this page in a single edit. Please discuss changes on the talk page before implementing them.

Usage

{{Str left|<string>|<count>}}

Gives the <count> substring of characters from the start of the trimmed string (the substring has length <count>).

If <count> is invalid or empty, an empty string is returned. If undefined, it defaults to 1.

Limitations

• Length to 500: The maximum substring stops at 500 long, yet gives no error message. Only 500 characters can be extracted even if the <string> is longer.
• Inexpensive (uses no other templates).

Examples

• {{ Str left | Lorem ipsum dolor sit amet | 10 }} → Lorem ipsu
• {{ Str left | Lorem ipsum dolor sit amet | 1 }} → L
• {{ Str left | Lorem ipsum dolor sit amet | 0 }} →
• {{ Str left | Lorem ipsum dolor sit amet | }} →
• {{ Str left | Lorem ipsum dolor sit amet }} → L
• {{ Str left | Lorem ipsum dolor sit amet | 40 }} → Lorem ipsum dolor sit ametLorem ipsum do
• {{ Str left | àçé | 2 }} → àç

  This example is demonstrating the safety of this template with the UTF-8 encoding (this should work now) :

Examples of limitations

All the limitations of use for this template and shown below are caused by the current implementation of the {{padleft:}} parser function used in this template, which does not filter its third parameter containing the characters used for padding a string to the specified length (it currently counts incorrectly the characters to extract from the padding string, and incorrectly measures its effective length; in addition this parameter is limited to 500 bytes).

The following examples are demonstrating that this template is not safe with character entity references found in its string parameter :

• {{ Str left | a c | 3 }} → a&n

  This should display "a c", but the named character entity was partially truncated, leaving no length available for the final "c".

• {{ Str left | aBc | 3 }} → a&#

  This should display "abc", but the named character entity was partially truncated, leaving no length available for the final "c".

• {{ Str left | a c | 3 }} → a c

  The result is correct, as expected.

• {{ Str left | a c | 3 }} → a&#

  This last example should be equivalent to the previous one, but it is not.

The following example shows that the presence of some wiki markup that should be transparent and ignored, does not allow this template to work as expected (the nowiki section is replaced by a unique index string in the effective runtime value of the parameter ; this unique (43-bytes long) string starts by a control character (which will be finally filtered out from the generated HTML page if it remains in the result of this template), followed by "UNIQ" and some unique sequence and terminated by "QINU" and a final control character ; it is partially visible below, because the unique string is not complete after truncation, and then cannot be eliminated from the output in the first two lines):

• {{ Str left | a<nowiki/>bc | 3 }} → abc

  It effectively returns 3 bytes, but the \x07 (BELL) control in the second position is stripped out when generating the HTML displayed here.

• {{ Str left | a<nowiki/>bc | 43 }} → abcabcabcabcabcabcabcabcabcabcabcabcabcabca

  It effectively returns 43 bytes, but the \x07 (BELL) control in the second position is stripped out when generating the HTML displayed here, and the final \x07 was truncated

• {{ Str left | a<nowiki/>bc | 44 }} → abcabcabcabcabcabcabcabcabcabcabcabcabcabcab

  It effectively returns 44 bytes, but the complete 43-bytes sequence is filtered out from the output wiki code when generating the final HTML, so there just remains the first leading "a" character .

• {{ Str left | a<nowiki/>bc | 45 }} → abcabcabcabcabcabcabcabcabcabcabcabcabcabcabc

On the opposite, the HTML comments, and the "noinclude", "includeonly" and "onlyinclude" wiki markup tags are safe, because they are preprocessed in template parameters, before including it and substituing parameters:

• {{ Str left | a<noinclude/>bc | 3 }} → abc
• {{ Str left | a<!-- comment -->bc | 3 }} → abc

Note also that the specified length will cause the input string to be padded by repeating it, it this length is larger than the input string length:

• {{ Str left | Abc. | 10 }} → Abc.Abc.Ab

See also

Trimming templates:

• {{Trunc}} – To trim down to a specified number of characters.
• {{Trim}} — To trim any leading or trailing whitespace.
• {{Str left}} – To trim down to a specified number of characters, or duplicate the string to a specified number.
• {{Str right}}
• {{Strip}} – To strip (remove) a given number of characters from the beginning/end of the string

Analyzing templates:

• {{Str endswith}} – To check if a string ends with a given string.
• {{Str find}} – Returns the numerical location of a given string in a string, up to 50 characters.
• {{Str len}} – Returns a string's length. Can count up to 500 characters.

String length comparison templates:

• {{Str ≤ len}} – To check if a string is "shorter or equally long" or "longer" than a given length.

Sandboxes and test cases:

• {{Str len/sandbox}}
• {{Str len/testcases}}

Technical stuff:

• mw:Help:Magic words – About {{padleft:|}}.
• mw:Help:Extension:ParserFunctions – About {{#titleparts:|}}, {{#expr:|}}, {{#ifeq:|}}, etc.
• Module:String - Script with native string parsing

• Bugzilla:22555 - need for correcting padleft and padright functions, and to provide better string handling parser functions.