Module:String

This module is intended to provide access to basic string functions.

Most of the functions provided here can be invoked with named parameters, unnamed parameters, or a mixture. If named parameters are used, MediaWiki will automatically remove any leading or trailing whitespace from the parameter. Depending on the intended use, it may be advantageous to either preserve or remove such whitespace.
For example, when a pattern should be replaced by something, that replacement may be wished by a space (whitespace), or by an empty string (removed whtespace).

Global options

ignore_errors

If set to 'true' or 1, any error condition will result in an empty string being returned rather than an error message.

error_category

If an error occurs, specifies the name of a category to include with the error message. The default category is Category:Errors reported by Module String.

no_category

If set to 'true' or 1, no category will be added if an error is generated.

Unit tests for this module are available at Module:String/testcases.

len

This function returns the length of the target string.

Usage:

{{#invoke:String|len|target_string}}

OR

{{#invoke:String|len|s=target_string}}

Parameters:

s

The string whose length to report

sub

This function returns a substring of the target string at specified indices.

Usage:

{{#invoke:String|sub|target_string|start_index|end_index}}

OR

{{#invoke:String|sub|s=target_string|i=start_index|j=end_index}}

Parameters:

s

The string to return a subset of

i

The first index of the substring to return, defaults to 1.

j

The last index of the string to return, defaults to the last character.

The first character of the string is assigned an index of 1. If either i or j is a negative value, it is interpreted the same as selecting a character by counting from the end of the string. Hence, a value of -1 is the same as selecting the last character of the string.

If the requested indices are out of range for the given string, an error is reported.

sublength

This function implements the features of {{Str sub old}} and is kept in order to maintain these older templates.

match

This function returns a substring from the source string that matches a specified pattern.

Usage:

{{#invoke:String|match|source_string|pattern_string|start_index|match_number|plain_flag
|nomatch_output}}

OR

{{#invoke:String|match|s=source_string|pattern=pattern_string|start=start_index
|match=match_number|plain=plain_flag|nomatch=nomatch_output}}

Parameters:

s

The string to search

pattern

The pattern or string to find within the string

start

The index within the source string to start the search. The first character of the string has index 1. Defaults to 1.

match

In some cases it may be possible to make multiple matches on a single string. This specifies which match to return, where the first match is match= 1. If a negative number is specified then a match is returned counting from the last match. Hence match = -1 is the same as requesting the last match. Defaults to 1.

plain

A flag indicating that the pattern should be understood as plain text. Defaults to false.

nomatch

If no match is found, output the "nomatch" value rather than an error.

If the match_number or start_index are out of range for the string being queried, then this function generates an error. An error is also generated if no match is found. If one adds the parameter ignore_errors=true, then the error will be suppressed and an empty string will be returned on any failure.

For information on constructing Lua patterns, a form of regular expression, see:

• http://www.lua.org/manual/5.1/manual.html#5.4.1
• Template:W#patterns
• Template:W#ustring patterns

pos

This function returns a single character from the target string at position pos.

Usage:

{{#invoke:String|pos|target_string|index_value}}

OR

{{#invoke:String|pos|target=target_string|pos=index_value}}

Parameters:

target

The string to search

pos

The index for the character to return

The first character has an index value of 1.

If one requests a negative value, this function will select a character by counting backwards from the end of the string. In other words pos = -1 is the same as asking for the last character.

A requested value of zero, or a value greater than the length of the string returns an error.

str_find

This function duplicates the behavior of {{str_find}}, including all of its quirks. This is provided in order to support existing templates, but is NOT RECOMMENDED for new code and templates. New code is recommended to use the "find" function instead.

Returns the first index in "source" that is a match to "target". Indexing is 1-based, and the function returns -1 if the "target" string is not present in "source".

Important Note: If the "target" string is empty / missing, this function returns a value of "1", which is generally unexpected behavior, and must be accounted for separatetly.

find

This function allows one to search for a target string or pattern within another string.

Usage:

{{#invoke:String|find|source_str|target_string|start_index|plain_flag}}

OR

{{#invoke:String|find|source=source_str|target=target_str|start=start_index
|plain=plain_flag}}

Parameters:

source

The string to search

target

The string or pattern to find within source

start

The index within the source string to start the search, defaults to 1

plain

Boolean flag indicating that target should be understood as plain text and not as a Lua-style regular expression, defaults to true

This function returns the first index >= "start" where "target" can be found within "source". Indices are 1-based. If "target" is not found, then this function returns 0. If either "source" or "target" are missing / empty, this function also returns 0.

This function should be safe for UTF-8 strings.

replace

This function allows one to replace a target string or pattern within another string.

Usage:

{{#invoke:String|replace|source_str|pattern_string|replace_string|replacement_count|plain_flag}}

OR

{{#invoke:String|replace|source= source_string |pattern= pattern_string

|replace= replace_string |count= replacement_count |plain= plain_flag }}

Parameters:

source

The string to search

pattern

The string or pattern to find within source

replace

The replacement text

count

The number of occurences to replace, defaults to all.

plain

Boolean flag indicating that pattern should be understood as plain text and not as a Lua-style regular expression, defaults to true

rep

Repeats a string n times. A simple function to pipe string.rep to templates. Usage:

{{#invoke:String|rep|source|count}}

Parameters:

source

The string to repeat

count

The number of repetitions.

Example {{#invoke:String|rep|hello|3}} gives

isNumber

Checks if string is a number Usage:

{{#invoke:String|isNumber|string}}

Parameters:

string

The string to test

Example {{#invoke:String|isNumber|hello}} gives , while {{#invoke:String|isNumber|-200e-5}} gives

---

local str = {}

function str.len( frame )
    return mw.ustring.len( frame.args.s )
end

function str.sub( frame )
    return mw.ustring.sub( frame.args.s, tonumber( frame.args.i ), tonumber( frame.args.j ) )
end

function str.sublength( frame )
    local i = tonumber( frame.args.i ) or 0
    local len = tonumber( frame.args.len )
    return mw.ustring.sub( frame.args.s, i + 1, len and ( i + len ) )
end

function str.match( frame )
    return mw.ustring.match( frame.args.s, frame.args.pattern, tonumber( frame.args.i ) )
end

--[====[
pos

This function returns a single character from the target string at position pos.

Usage:
{{#invoke:String|pos|target_string|index_value}}
OR
{{#invoke:String|pos|target=target_string|pos=index_value}}

Parameters
    target: The string to search
    pos: The index for the character to return

If invoked using named parameters, Mediawiki will automatically remove any leading or
trailing whitespace from the target string.  In some circumstances this is desirable, in 
other cases one may want to preserve the whitespace.

The first character has an index value of 1.

If one requests a negative value, this function will select a character by counting backwards 
from the end of the string.  In other words pos = -1 is the same as asking for the last character.

A requested value of zero, or a value greater than the length of the string returns an error.
]====]
function str.pos( frame )
    local new_args = str._getParameters( frame.args, {'target', 'pos'} );
    local target_str = new_args['target'] or '';
    local pos = tonumber( new_args['pos'] ) or 0;

    if pos == 0 or math.abs(pos) > mw.ustring.len( target_str ) then
        return '<strong class="error">String index out of range</strong>';
    end    
    
    return mw.ustring.sub( target_str, pos, pos );
end

--[====[
str_find

This function duplicates the behavior of {{str_find}}, including all of its quirks.
This is provided in order to support existing templates, but is NOT RECOMMENDED for 
new code and templates.  New code is recommended to use the "find" function instead.

Returns the first index in "source" that is a match to "target".  Indexing is 1-based,
and the function returns -1 if the "target" string is not present in "source".

Important Note: If the "target" string is empty / missing, this function returns a
value of "1", which is generally unexpected behavior, and must be accounted for
separatetly.
]====]
function str.str_find( frame )
    local new_args = str._getParameters( frame.args, {'source', 'target'} );
    local source_str = new_args['source'] or '';
    local target_str = new_args['target'] or '';

    if target_str == '' then
        return 1;
    end    
    
    local start = mw.ustring.find( source_str, target_str, 1, true )
    if start == nil then
        start = -1
    end
    
    return start
end

--[====[
find

This function allows one to search for a target string or pattern within another
string.

Usage:
{{#invoke:String|find|source_str|target_string|start_index|plain_flag}}
OR
{{#invoke:String|find|source=source_str|target=target_str|start=start_index|plain=plain_flag}}

Parameters
    source: The string to search
    target: The string or pattern to find within source
    start: The index within the source string to start the search, defaults to 1
    plain: Boolean flag indicating that target should be understood as plain
        text and not as a Lua style regular expression, defaults to true

If invoked using named parameters, Mediawiki will automatically remove any leading or
trailing whitespace from the parameter.  In some circumstances this is desirable, in 
other cases one may want to preserve the whitespace.

This function returns the first index >= "start" where "target" can be found 
within "source".  Indices are 1-based.  If "target" is not found, then this 
function returns 0.  If either "source" or "target" are missing / empty, this
function also returns 0.

This function should be safe for UTF-8 strings.
]====]
function str.find( frame )
    local new_args = str._getParameters( frame.args, {'source', 'target', 'start', 'plain' } ); 
    local source_str = new_args['source'] or '';
    local pattern = new_args['target'] or '';
    local start_pos = tonumber(new_args['start']) or 1;
    local plain = new_args['plain'] or true;
        
    if source_str == '' or pattern == '' then
        return 0;
    end    
    
    plain = str._getBoolean( plain );

    local start = mw.ustring.find( source_str, pattern, start_pos, plain )
    if start == nil then
        start = 0
    end
    
    return start
end

--[====[
replace

This function allows one to replace a target string or pattern within another
string.

Usage:
{{#invoke:String|replace_plain|source_str|pattern_string|replace_string|replacement_count|pattern_flag}}
OR
{{#invoke:String|replace_plain|source=source_str|pattern=pattern_str|replace=replace_string|
   count=replacement_count|plain=pattern_flag}}

Parameters
    source: The string to search
    pattern: The string or pattern to find within source
    replace: The replacement text
    count: The number of occurences to replace, defaults to all.
    plain: Boolean flag indicating that pattern should be understood as plain
        text and not as a Lua style regular expression, defaults to true 
]====]
function str.replace( frame )
    local new_args = str._getParameters( frame.args, {'source', 'pattern', 'replace', 'count', 'plain' } ); 
    local source_str = new_args['source'] or '';
    local pattern = new_args['pattern'] or '';
    local replace = new_args['replace'] or '';
    local count = tonumber( new_args['count'] );
    local plain = new_args['plain'] or true;
        
    if source_str == '' or pattern == '' then
        return source_str;
    end    
    plain = str._getBoolean( plain );

    if plain then
        pattern = str._escapePattern( pattern );
        replace = str._escapePattern( replace );
    end
    
    local result;

    if count ~= nil then
        result = mw.ustring.gsub( source_str, pattern, replace, count );
    else
        result = mw.ustring.gsub( source_str, pattern, replace );
    end        

    return result;
end

--[====[
Helper function that populates the argument list given that user may need to use a mix of
named and unnamed parameters.  This is relevant because named parameters are not
identical to unnamed parameters due to string trimming, and when dealing with strings
we sometimes want to either preserve or remove that whitespace depending on the application.
]====]
function str._getParameters( frame_args, arg_list )
    local new_args = {};
    local index = 1;
    local value;
    
    for i,arg in ipairs( arg_list ) do
        value = frame_args[arg]
        if value == nil then
            value = frame_args[index];
            index = index + 1;
        end
        new_args[arg] = value;
    end
    
    return new_args;
end        

--[====[
Helper Function to interpret boolean strings
]====]
function str._getBoolean( boolean_str )
    local boolean_value;
    
    if type( boolean_str ) == 'string' then
        boolean_str = boolean_str:lower();
        if boolean_str == 'false' or boolean_str == 'no' or boolean_str == '0' then
            boolean_value = false;
        else
            boolean_value = true;
        end    
    elseif type( boolean_str ) == 'boolean' then
        boolean_value = boolean_str;
    else
        error( 'No boolean value found' );
    end    
    return boolean_value
end

--[====[
Helper function that escapes all pattern characters so that they will be treated 
as plain text.
]====]
function str._escapePattern( pattern_str )
    return mw.ustring.gsub( pattern_str, "([%(%)%.%%%+%-%*%?%[%^%$%]])", "%%%1" );
end

return str