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 automatically removes 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 results 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 is 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.
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
- Boolean flag indicating that pattern should be understood as plain text and not as a Lua-style regular expression. 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 is suppressed and an empty string returned on any failure.
For information on constructing Lua patterns, a form of regular expression, see:
- Lua reference: Patterns (as of version 5.1)
- Scribunto patterns
- Scribunto Unicode string 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 selects 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.
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 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
rep
Repeats a string
Usage:
{{#invoke:String|rep|source|count}}
Parameters:
- source
- The string to repeat
- count
- The number of repetitions.
Example {{#invoke:String|rep|hello|3}}
gives hellohellohello
reverse
Reverse a string
Usage:
{{#invoke:String|reverse|target_string}}
OR
{{#invoke:String|reverse|s=target_string}}
Parameters
- s
- The string to reverse
--[[
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
automatically removes 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 results 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 is added if an error
is generated.
Unit tests for this module are available at Module:String/tests.
]]
local str = {}
--[[
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.
]]
local function _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
]]
local function _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 to handle error messages.
]]
local function _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 _getBoolean(ignore_errors) then
return ''
end
local error_str = '<strong class="lua-error">String Module Error: ' .. error_str .. '</strong>'
if error_category ~= '' and not _getBoolean( no_category ) then
error_str = '[[Category:' .. error_category .. ']]' .. error_str
end
return error_str
end
--[[
Helper function that escapes all pattern characters so that they are treated
as plain text.
]]
local function _escapePattern( pattern_str )
return mw.ustring.gsub( pattern_str, "([%(%)%.%%%+%-%*%?%[%^%$%]])", "%%%1" )
end
--[[
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 automatically removes any leading or
trailing whitespace from the target string.
]]
function str.len( frame )
local new_args = _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 = _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 _error( 'String subset index out of range' )
end
if j < i then
return _error( 'String subset indices out of order' )
end
return mw.ustring.sub( s, i, j )
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 automatically removes 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 is suppressed and
an empty string 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
]]
function str.match( frame )
local new_args = _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 = _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']
if s == '' then
return _error( 'Target string is empty' )
end
if pattern == '' then
return _error( 'Pattern string is empty' )
end
if math.abs(start) < 1 or math.abs(start) > mw.ustring.len( s ) then
return _error( 'Requested start is out of range' )
end
if match_index == 0 then
return _error( 'Match index is out of range' )
end
if plain_flag then
pattern = _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 _error( 'Match not found' )
else
return nomatch
end
else
return result
end
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 automatically removes 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 selects 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 = _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 _error( 'String index out of range' )
end
return mw.ustring.sub( target_str, pos, pos )
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 automatically removes 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 = _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 = _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_string|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 = _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 = _getBoolean( plain )
if plain then
pattern = _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
--[[
rep
Repeats a string
Usage:
{{#invoke:String|rep|source|count}}
Parameters
source: The string to repeat
count: The number of repetitions
Invocation supports only unnamed parameters.
]]
function str.rep( frame )
local repetitions = tonumber( frame.args[2] )
if not repetitions then
return _error( 'function rep expects a number as second parameter, received "' .. ( frame.args[2] or '' ) .. '"' )
end
return string.rep( frame.args[1] or '', repetitions )
end
--[[
reverse
Reverse a string
Usage:
{{#invoke:String|reverse|target_string}}
OR
{{#invoke:String|reverse|s=target_string}}
Parameters
s: The string to reverse
If invoked using named parameters, Mediawiki automatically removes any leading or
trailing whitespace from the target string.
]]
function str.reverse ( frame )
local new_args = _getParameters( frame.args, { 's' } )
local s = new_args['s'] or ''
local len = mw.ustring.len( s )
local result = {}
for i = len, 1, -1 do
-- strings are immutable in Lua, so use a table ...
table.insert( result, mw.ustring.sub( s, i, i ) )
end
-- ... and implode/join it
return table.concat( result )
end
return str