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    Farthest Frontier

    Module:String (edit | talk | history | links | watch | logs)

    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.

    Global options[edit source]

    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 (0).
    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[edit source]

    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

    Examples:

    • {{#invoke:String|len| abcdefghi }} → 11
    • {{#invoke:String|len|s= abcdefghi }} → 9

    sub[edit source]

    This function returns a substring of the target string at specified inclusive, one-indexed 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. To avoid error messages, use {{#invoke:ustring|sub}} instead.

    Examples:

    • "{{#invoke:String|sub| abcdefghi }}" → " abcdefghi "
    • "{{#invoke:String|sub|s= abcdefghi }}" → "abcdefghi"
    • "{{#invoke:String|sub| abcdefghi | 3 }}" → "bcdefghi "
    • "{{#invoke:String|sub|s= abcdefghi |i= 3 }}" → "cdefghi"
    • "{{#invoke:String|sub| abcdefghi | 3 | 4 }}" → "bc"
    • "{{#invoke:String|sub|s= abcdefghi |i= 3 |j= 4 }}" → "cd"

    sublength[edit source]

    This function implements the features of {{str sub old}} and is kept in order to maintain these older templates. It returns a substring of the target string starting at a specified index and of a specified length.

    Usage:

    {{#invoke:String|sublength|s= target_string |i= start_index |len= length }}

    Parameters:

    s
    The string
    i
    The starting index of the substring to return. The first character of the string is assigned an index of 0.
    len
    The length of the string to return, defaults to the last character.

    Examples:

    • {{#invoke:String|sublength|s= abcdefghi }} → abcdefghi
    • {{#invoke:String|sublength|s= abcdefghi |i= 3 }} → defghi
    • {{#invoke:String|sublength|s= abcdefghi |i= 3 |len= 4 }} → defg

    match[edit source]

    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
    Boolean flag indicating that pattern should be understood as plain text and not as a Scribunto ustring pattern (a unicode-friendly Lua-style regular expression). Defaults to false (to change: plain=true)
    nomatch
    If no match is found, output the "nomatch" value rather than an error.
    ignore_errors
    If no match is found and ignore_errors=true, output an empty string 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:

    Examples:

    • {{#invoke:String|match| abc123def456 |%d+}} → 123
    • {{#invoke:String|match|s= abc123def456 |pattern= %d+ }} → 123
    • {{#invoke:String|match| abc123def456 |%d+|6}} → 23
    • {{#invoke:String|match|s= abc123def456 |pattern= %d+ |start= 6 }} → 3
    • {{#invoke:String|match|s= abc123def456 |pattern= %d+ |start= 6 |match= 2 }} → 456
    • {{#invoke:String|match|s= abc123%d+ |pattern= %d+ }} → 123
    • {{#invoke:String|match|s= abc123%d+ |pattern= %d+ |plain= true }} → %d+
    • {{#invoke:String|match|s= abc |pattern= %d }}String Module Error: Match not found
    • {{#invoke:String|match|s= abc |pattern= %d |nomatch= No numeric characters in string }} → No numeric characters in string
    • {{#invoke:String|match|s= abc |pattern= %d |ignore_errors= true }}
    • {{#invoke:String|match|s= 0012001200 |pattern= 0*(%d*) }} → 12001200

    pos[edit source]

    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.

    Examples:

    • {{#invoke:String|pos| abcdefghi | 4 }} → c
    • {{#invoke:String|pos|target= abcdefghi |pos= 4 }} → d

    str_find[edit source]

    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 separately.

    Usage:

    {{#invoke:String|str_find|source_string|target_string}}

    OR

    {{#invoke:String|str_find|source= source_string |target= target_string }}

    Parameters:

    source
    The string to search
    target
    The string to find within source

    Examples:

    • {{#invoke:String|str_find| abc123def }} → 1
    • {{#invoke:String|str_find|source= abc123def }} → 1
    • {{#invoke:String|str_find| abc123def |123}} → 5
    • {{#invoke:String|str_find|source= abc123def |target= 123 }} → 4
    • {{#invoke:String|str_find| abc123def |not}} → -1

    find[edit source]

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

    Usage:

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

    OR

    {{#invoke:String|find|source= source_string |target= target_string |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 Scribunto ustring pattern (a unicode-friendly 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.

    Examples:

    • {{#invoke:String|find|abc123def|12}} → 4
    • {{#invoke:String|find|source=abc123def|target=12}} → 4
    • {{#invoke:String|find|source=abc123def|target=pqr}} → 0
    • {{#invoke:String|find| abc123def |123}} → 5
    • {{#invoke:String|find|source= abc123def |target= 123 }} → 4
    • {{#invoke:String|find|source=abc123def|target=%d |start=3 |plain=false }} → 4

    When using unnamed parameters, preceding and trailing spaces are kept and counted:

    • {{#invoke:String|find| abc123def |c|false}} → 5
    • {{#invoke:String|find|source= abc123def |target=c|plain=false}} → 3
    • {{#invoke:string|find|abc 123 def|%s|plain=false}} → 4

    Testing for the presence of a string:

    • {{#ifexpr:{{#invoke:string|find|haystack|needle}}|Found needle|Didn't find needle}} → Didn't find needle

    replace (gsub)[edit source]

    This function allows one to replace a target string or pattern within another string. To Lua programmers: this function works internally by calling string.gsub.

    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 occurrences to replace; defaults to all
    plain
    Boolean flag indicating that pattern should be understood as plain text and not as a Scribunto ustring pattern (a unicode-friendly Lua-style regular expression); defaults to true

    Examples:

    • "{{#invoke:String|replace| abc123def456 |123|XYZ}}" → " abcXYZdef456 "
    • "{{#invoke:String|replace|source= abc123def456 |pattern= 123 |replace= XYZ }}" → "abcXYZdef456"
    • "{{#invoke:String|replace| abc123def456 |%d+|XYZ|1|false}}" → " abcXYZdef456 "
    • "{{#invoke:String|replace|source= abc123def456 |pattern= %d+ |replace= XYZ |count=1 |plain= false }}" → "abcXYZdef456"
    • "{{#invoke:String|replace|source= abc123def456 |pattern= %d+ |replace= XYZ |plain= false }}" → "abcXYZdefXYZ"
    • {{#invoke:String|replace|source= 0012001200 |pattern= ^0* |plain= false }} → 12001200

    rep[edit source]

    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.

    Examples:

    • "{{#invoke:String|rep|hello|3}}" → "hellohellohello"
    • "{{#invoke:String|rep| hello | 3 }}" → " hello hello hello "

    escapePattern[edit source]

    In a Lua pattern, changes a class character into a literal character. For example: in a pattern, character . catches "any character"; escapePattern will convert it to %., catching just the literal character ".".

    Usage:

    • {{#invoke:String|escapePattern|pattern_string}}

    Parameters:

    pattern_string
    The pattern string to escape

    Examples:

    • "{{#invoke:String|escapePattern|A.D.}}" → "A%.D%."
    • "{{#invoke:String|escapePattern|10%}}" → "10%%"

    count[edit source]

    Counts the number of times a given pattern appears in the arguments that get passed on to this module. Counts disjoint matches only.

    Usage:

    {{#invoke:String|count|source_str|pattern_string|plain_flag}}

    OR

    {{#invoke:String|count|source= source_string |pattern= pattern_string|plain= plain_flag }}

    Parameters:

    source_string
    The string to count occurrences in
    pattern
    The string or pattern to count occurrences of within source
    plain
    Boolean flag indicating that pattern should be understood as plain text and not as a Scribunto ustring pattern (a unicode-friendly Lua-style regular expression); defaults to true

    Examples:

    • Count of 'a': "{{#invoke:String|count|aabbcc|a}}" → "2"
    • Count occurrences of 'aba': "{{#invoke:String|count|ababababab|aba}}" → "2"
    • Count of "either 'a' or 'c' ":"{{#invoke:String|count|aabbcc|[ac]|plain=false}}" → "4"
    • Count of "not 'a' ": "{{#invoke:String|count|aaabaaac|[^a]|plain=false}}" → "2"
    • Count of "starts with 'a' ": "{{#invoke:String|count|aaabaaac|^a|plain=false}}" → "1"

    join[edit source]

    Joins all strings passed as arguments into one string, treating the first argument as a separator

    Usage:

    {{#invoke:String|join|separator|string1|string2|...}}

    Parameters:

    separator
    String that separates each string being joined together
    Note that leading and trailing spaces are not stripped from the separator.
    string1/string2/...
    Strings being joined together

    Examples:

    • "{{#invoke:String|join|x|foo|bar|baz}}" → "fooxbarxbaz"
    • "{{#invoke:String|join||a|b|c|d|e|f|g}}" → "abcdefg"
    • "{{#invoke:String|join|,|a|b|c|d|e|f|g}}" → "a,b,c,d,e,f,g"
    • "{{#invoke:String|join|, |a|b|c|d|e|f|g}}" → "a, b, c, d, e, f, g"
    • "{{#invoke:String|join| – |a|b|c|d|e|f|g}}" → "a – b – c – d – e – f – g"

    The preceding example uses the html entity – but the unicode character also works.

    endswith[edit source]

    Usage:

    {{#invoke:String|endswith|source_str|search_string}}

    OR

    {{#invoke:String|endswith|source= source_string |pattern= search_string}}

    Returns "yes" if the source string ends with the search string. Use named parameters to have the strings trimmed before use. Despite the parameter name, search_string is not a Lua pattern, it is interpreted literally.

    • "{{#invoke:String|endswith|xxxyyy|y}}" → "yes"
    • "{{#invoke:String|endswith|xxxyyy|z}}" → ""

    See also[edit source]

    Template:String handling templates


    --[[
    
    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.
    
    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/tests.
    ]]
    
    local str = {}
    
    --[[
    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
    
    If invoked using named parameters, Mediawiki will automatically remove any leading or
    trailing whitespace from the target string.
    ]]
    function str.len( frame )
    	local new_args = str._getParameters( frame.args, {'s'} )
    	local s = new_args['s'] or ''
    	return mw.ustring.len( s )
    end
    
    --[[
    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 fist 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.
    ]]
    function str.sub( frame )
    	local new_args = str._getParameters( frame.args, { 's', 'i', 'j' } )
    	local s = new_args['s'] or ''
    	local i = tonumber( new_args['i'] ) or 1
    	local j = tonumber( new_args['j'] ) or -1
    
    	local len = mw.ustring.len( s )
    
    	-- Convert negatives for range checking
    	if i < 0 then
    		i = len + i + 1
    	end
    	if j < 0 then
    		j = len + j + 1
    	end
    
    	if i > len or j > len or i < 1 or j < 1 then
    		return str._error( 'String subset index out of range' )
    	end
    	if j < i then
    		return str._error( 'String subset indices out of order' )
    	end
    
    	return mw.ustring.sub( s, i, j )
    end
    
    --[[
    This function implements that features of {{str sub old}} and is kept in order
    to maintain these older templates.
    ]]
    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
    
    --[[
    _match
    
    This function returns a substring from the source string that matches a
    specified pattern. It is exported for use in other modules
    
    Usage:
    strmatch = require("Module:String")._match
    sresult = strmatch( s, pattern, start, match, plain, nomatch )
    
    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.
    
    For information on constructing Lua patterns, a form of [regular expression], see:
    
    * http://www.lua.org/manual/5.1/manual.html#5.4.1
    * http://www.mediawiki.org/wiki/Extension:Scribunto/Lua_reference_manual#Patterns
    * http://www.mediawiki.org/wiki/Extension:Scribunto/Lua_reference_manual#Ustring_patterns
    
    ]]
    -- This sub-routine is exported for use in other modules
    function str._match( s, pattern, start, match_index, plain_flag, nomatch )
    	if s == '' then
    		return str._error( 'Target string is empty' )
    	end
    	if pattern == '' then
    		return str._error( 'Pattern string is empty' )
    	end
    	start = tonumber(start) or 1
    	if math.abs(start) < 1 or math.abs(start) > mw.ustring.len( s ) then
    		return str._error( 'Requested start is out of range' )
    	end
    	if match_index == 0 then
    		return str._error( 'Match index is out of range' )
    	end
    	if plain_flag then
    		pattern = str._escapePattern( pattern )
    	end
    
    	local result
    	if match_index == 1 then
    		-- Find first match is simple case
    		result = mw.ustring.match( s, pattern, start )
    	else
    		if start > 1 then
    			s = mw.ustring.sub( s, start )
    		end
    
    		local iterator = mw.ustring.gmatch(s, pattern)
    		if match_index > 0 then
    			-- Forward search
    			for w in iterator do
    				match_index = match_index - 1
    				if match_index == 0 then
    					result = w
    					break
    				end
    			end
    		else
    			-- Reverse search
    			local result_table = {}
    			local count = 1
    			for w in iterator do
    				result_table[count] = w
    				count = count + 1
    			end
    
    			result = result_table[ count + match_index ]
    		end
    	end
    
    	if result == nil then
    		if nomatch == nil then
    			return str._error( 'Match not found' )
    		else
    			return nomatch
    		end
    	else
    		return result
    	end
    end
    
    --[[
    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 invoked using named parameters, Mediawiki will automatically remove any leading or
    trailing whitespace from each string.  In some circumstances this is desirable, in
    other cases one may want to preserve the whitespace.
    
    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
    * http://www.mediawiki.org/wiki/Extension:Scribunto/Lua_reference_manual#Patterns
    * http://www.mediawiki.org/wiki/Extension:Scribunto/Lua_reference_manual#Ustring_patterns
    
    ]]
    -- This is the entry point for #invoke:String|match
    function str.match( frame )
    	local new_args = str._getParameters( frame.args, {'s', 'pattern', 'start', 'match', 'plain', 'nomatch'} )
    	local s = new_args['s'] or ''
    	local start = tonumber( new_args['start'] ) or 1
    	local plain_flag = str._getBoolean( new_args['plain'] or false )
    	local pattern = new_args['pattern'] or ''
    	local match_index = math.floor( tonumber(new_args['match']) or 1 )
    	local nomatch = new_args['nomatch']
    
    	return str._match( s, pattern, start, match_index, plain_flag, nomatch )
    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 str._error( 'String index out of range' )
    	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|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
    ]]
    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 = mw.ustring.gsub( replace, "%%", "%%%%" ) --Only need to escape replacement sequences.
    	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
    
    --[[
        simple function to pipe string.rep to templates.
    ]]
    function str.rep( frame )
    	local repetitions = tonumber( frame.args[2] )
    	if not repetitions then
    		return str._error( 'function rep expects a number as second parameter, received "' .. ( frame.args[2] or '' ) .. '"' )
    	end
    	return string.rep( frame.args[1] or '', repetitions )
    end
    
    --[[
    escapePattern
    
    This function escapes special characters from a Lua string pattern. See [1]
    for details on how patterns work.
    
    [1] https://www.mediawiki.org/wiki/Extension:Scribunto/Lua_reference_manual#Patterns
    
    Usage:
    {{#invoke:String|escapePattern|pattern_string}}
    
    Parameters
        pattern_string: The pattern string to escape.
    ]]
    function str.escapePattern( frame )
    	local pattern_str = frame.args[1]
    	if not pattern_str then
    		return str._error( 'No pattern string specified' )
    	end
    	local result = str._escapePattern( pattern_str )
    	return result
    end
    
    --[[
    count
    This function counts the number of occurrences of one string in another.
    ]]
    function str.count(frame)
    	local args = str._getParameters(frame.args, {'source', 'pattern', 'plain'})
    	local source = args.source or ''
    	local pattern = args.pattern or ''
    	local plain = str._getBoolean(args.plain or true)
    	if plain then
    		pattern = str._escapePattern(pattern)
    	end
    	local _, count = mw.ustring.gsub(source, pattern, '')
    	return count
    end
    
    --[[
    endswith
    This function determines whether a string ends with another string.
    ]]
    function str.endswith(frame)
    	local args = str._getParameters(frame.args, {'source', 'pattern'})
    	local source = args.source or ''
    	local pattern = args.pattern or ''
    	if pattern == '' then
    		-- All strings end with the empty string.
    		return "yes"
    	end
    	if mw.ustring.sub(source, -mw.ustring.len(pattern), -1) == pattern then
    		return "yes"
    	else
    		return ""
    	end
    end
    
    --[[
    join
    
    Join all non empty arguments together; the first argument is the separator.
    Usage:
    {{#invoke:String|join|sep|one|two|three}}
    ]]
    function str.join(frame)
    	local args = {}
    	local sep
    	for _, v in ipairs( frame.args ) do
    		if sep then
    			if v ~= '' then
    				table.insert(args, v)
    			end
    		else
    			sep = v
    		end
    	end
    	return table.concat( args, sep or '' )
    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 _, 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 handle error messages.
    ]]
    function str._error( error_str )
    	local frame = mw.getCurrentFrame()
    	local error_category = frame.args.error_category or 'Errors reported by Module String'
    	local ignore_errors = frame.args.ignore_errors or false
    	local no_category = frame.args.no_category or false
    
    	if str._getBoolean(ignore_errors) then
    		return ''
    	end
    
    	local error_str = '<strong class="error">String Module Error: ' .. error_str .. '</strong>'
    	if error_category ~= '' and not str._getBoolean( no_category ) then
    		error_str = '[[Category:' .. error_category .. ']]' .. error_str
    	end
    
    	return error_str
    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'
    				or boolean_str == '' 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
    
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