--- title: "StringTemplate" language: "en" type: "Symbol" summary: "StringTemplate[string] yields a TemplateObject expression that represents a string template to be applied to arguments. StringTemplate[src] uses File[...], URL[...] or CloudObject[...] as the source for the string template. StringTemplate[form, args] yields a TemplateObject with arguments, suitable for cloud deployment or other evaluation." keywords: - templating - string pattern - natural language generation - NLG - fill in string - evaluate in string canonical_url: "https://reference.wolfram.com/language/ref/StringTemplate.html" source: "Wolfram Language Documentation" related_guides: - title: "Working with Templates" link: "https://reference.wolfram.com/language/guide/WorkingWithTemplates.en.md" - title: "String Manipulation" link: "https://reference.wolfram.com/language/guide/StringManipulation.en.md" - title: "Text Generation" link: "https://reference.wolfram.com/language/guide/TextConstruction.en.md" - title: "Text Manipulation" link: "https://reference.wolfram.com/language/guide/ProcessingTextualData.en.md" - title: "Notebook Document Generation" link: "https://reference.wolfram.com/language/guide/DocumentGeneration.en.md" - title: "External Interpreted Language Interfaces" link: "https://reference.wolfram.com/language/guide/ExternalInterpretedLanguageInterfaces.en.md" - title: "External Language Interfaces" link: "https://reference.wolfram.com/language/guide/ExternalLanguageInterfaces.en.md" - title: "LLM-Related Functionality" link: "https://reference.wolfram.com/language/guide/LLMFunctions.en.md" related_workflows: - title: "Create a Webpage with Templates" link: "https://reference.wolfram.com/language/workflow/CreateAWebpageWithTemplates.en.md" related_functions: - title: "FileTemplate" link: "https://reference.wolfram.com/language/ref/FileTemplate.en.md" - title: "XMLTemplate" link: "https://reference.wolfram.com/language/ref/XMLTemplate.en.md" - title: "TemplateApply" link: "https://reference.wolfram.com/language/ref/TemplateApply.en.md" - title: "StringReplace" link: "https://reference.wolfram.com/language/ref/StringReplace.en.md" - title: "StringJoin" link: "https://reference.wolfram.com/language/ref/StringJoin.en.md" - title: "StringRiffle" link: "https://reference.wolfram.com/language/ref/StringRiffle.en.md" - title: "Pluralize" link: "https://reference.wolfram.com/language/ref/Pluralize.en.md" - title: "StringForm" link: "https://reference.wolfram.com/language/ref/StringForm.en.md" --- # StringTemplate StringTemplate["string"] yields a TemplateObject expression that represents a string template to be applied to arguments. StringTemplate[src] uses File[…], URL[…] or CloudObject[…] as the source for the string template. StringTemplate[form, args] yields a TemplateObject with arguments, suitable for cloud deployment or other evaluation. ## Details and Options * The following special forms can be used inside the string: | | | | ---------- | ---------------------------------------------------------- | | `` | TemplateSlot[n], for n taking successive values 1, 2, 3, … | | `n` | TemplateSlot[n] | | `name` | TemplateSlot["name"] | | <\*expr\*> | TemplateExpression[expr] | * A ``StringTemplate`` object can be rendered using ``TemplateApply[StringTemplate[…], {e1, e2, …}]`` or using the form ``StringTemplate[…][e1, e2, …]``. * ``StringTemplate`` has the following options: | | | | | ------------------ | ---------- | ------------------------------------------------------------- | | CombinerFunction | StringJoin | function to apply to combine pieces before returning a result | | InsertionFunction | TextString | function or format to apply before inserting expressions | * In ``StringTemplate[File[…]]`` and ``StringTemplate[URL[…]]``, the content of the source file etc. is imported as a string. --- ## Examples (15) ### Basic Examples (4) Apply a string template with slots named ``a`` and ``b`` : ```wl In[1]:= StringTemplate["first `a` then `b`"][<|"a" -> 1234, "b" -> 5678|>] Out[1]= "first 1234 then 5678" ``` An equivalent form using ``TemplateApply`` : ```wl In[2]:= TemplateApply[StringTemplate["first `a` then `b`"], <|"a" -> 1234, "b" -> 5678|>] Out[2]= "first 1234 then 5678" ``` The ``StringTemplate`` is not needed inside ``TemplateApply`` : ```wl In[3]:= TemplateApply["first `a` then `b`", <|"a" -> 1234, "b" -> 5678|>] Out[3]= "first 1234 then 5678" ``` --- Apply a string template to positional arguments: ```wl In[1]:= StringTemplate["a is ``, b is ``"][5555, 6666] Out[1]= "a is 5555, b is 6666" ``` An equivalent form: ```wl In[2]:= StringTemplate["a is `1`, b is `2`"][5555, 6666] Out[2]= "a is 5555, b is 6666" ``` --- The expression inside `` < * ... * > `` is evaluated when the string template is applied: ```wl In[1]:= StringTemplate["Values: <* Range[5] *>."][] Out[1]= "Values: {1, 2, 3, 4, 5}." ``` Include a template slot as well as an expression in the template string: ```wl In[2]:= StringTemplate["Value `a`: <* Range[5] *>."][<|"a" -> 1234|>] Out[2]= "Value 1234: {1, 2, 3, 4, 5}." ``` Values from the association can be used in the template expression: ```wl In[3]:= StringTemplate["Value `a`: <* Range[#n] *>."][<|"a" -> 1234, "n" -> 3|>] Out[3]= "Value 1234: {1, 2, 3}." ``` Rule delayed can be used to delay computations: ```wl In[4]:= data = <|"a" :> RandomReal[]|>; TemplateApply["a is `a`", data] Out[4]= "a is 0.39568856" In[5]:= TemplateApply["my favorite number is `a`", data] Out[5]= "my favorite number is 0.14561387" ``` --- Expressions are spliced into the string using ``TextString`` : ```wl In[1]:= StringTemplate["First `` then ``"]["a string", \[FreeformPrompt]["a million miles"]] Out[1]= "First a string then 1000000 miles" ``` ### Scope (4) ``File`` is fully supported: ```wl In[1]:= StringTemplate[File["Examples/String/url.txt"]] Out[1]= TemplateObject[{"http://www.wolframalpha.com/input/?i=", TemplateSlot["input"]}, InsertionFunction -> TextString, CombinerFunction -> StringJoin] ``` --- Templates can be hosted in the Wolfram Cloud: ```wl In[1]:= template = CloudDeploy[StringTemplate["hello i'm `Name`"]] Out[1]= CloudObject["https://www.wolframcloud.com/obj/9e2cc434-380e-4b20-9492-66aafdf5b530"] ``` ``CloudObject`` can be directly used by ``TemplateApply`` : ```wl In[2]:= TemplateApply[template, <|"Name" -> "john"|>] Out[2]= "hello i'm john" ``` --- The second argument of ``StringTemplate`` can be used to bound data to the template: ```wl In[1]:= t = StringTemplate["a is `a`, b is `b`", <|"a" :> RandomReal[]|>]; TemplateApply[t] Out[1]= "a is 0.0193946, b is " In[2]:= TemplateApply[t, <|"b" :> RandomReal[]|>] Out[2]= "a is 0.674614, b is 0.908914" ``` --- ``URL`` can be used to fetch templates: ```wl In[1]:= template = URL @@ CloudExport["hi i'm `Name`", "String"] Out[1]= URL["https://www.wolframcloud.com/obj/26137869-ad07-46f8-9d27-326ae2388d7e"] In[2]:= URLRead[template, "Body"] Out[2]= "\"hi i'm `Name`\"" In[3]:= StringTemplate[template] Out[3]= TemplateObject[{"\"hi i'm ", TemplateSlot["Name"], "\""}, InsertionFunction -> TextString, CombinerFunction -> StringJoin] ``` ### Options (2) #### CombinerFunction (1) Specify a different way to combine parts of templates: ```wl In[1]:= t = StringTemplate[ "Best friend of `1` is `2`.", CombinerFunction -> Composition[ToUpperCase, StringJoin] ]; t["John", "Jane"] Out[1]= "BEST FRIEND OF JOHN IS JANE." ``` It can be used to return any expression, not only a string: ```wl In[2]:= t = StringTemplate[ "Best friend of `1` is `2`.", CombinerFunction -> Row ]; t["John", "Jane"] Out[2]= "Best friend of ""John"" is ""Jane""." In[3]:= t = StringTemplate[ "Best friend of `1` is `2`.", CombinerFunction -> Composition[Flatten, Characters] ]; t["John", "Jane"] Out[3]= {"B", "e", "s", "t", " ", "f", "r", "i", "e", "n", "d", " ", "o", "f", " ", "J", "o", "h", "n", " ", "i", "s", " ", "J", "a", "n", "e", "."} ``` #### InsertionFunction (1) Specify a function to convert arguments before they are inserted: ```wl In[1]:= t = StringTemplate[ "Best friend of `1` is `2`.", InsertionFunction -> ToUpperCase ]; t["John", "Jane"] Out[1]= "Best friend of JOHN is JANE." ``` You can use a string to specify an export format: ```wl In[2]:= t = StringTemplate[ "Data: `1`", InsertionFunction -> "JSON" ]; t[<|"name" -> "John", "profession" -> "WebDeveloper"|>] Out[2]= "Data: { \"name\": \"John\", \"profession\": \"WebDeveloper\" }" ``` ### Properties & Relations (3) ``StringTemplate`` evaluates to a ``TemplateObject`` : ```wl In[1]:= StringTemplate["Best friend of `1` is `2`."] Out[1]= TemplateObject[{"Best friend of ", TemplateSlot[1], " is ", TemplateSlot[2], "."}, InsertionFunction -> TextString, CombinerFunction -> StringJoin] ``` --- If you deploy a template with data, each time you visit it ``TemplateApply`` will render the content again: ```wl In[1]:= CloudDeploy[ StringTemplate[ "hello `Name`", <|"Name" :> If[$RequesterWolframID === None, "friend", $RequesterWolframID]|> ]] Out[1]= CloudObject["https://www.wolframcloud.com/obj/3142181b-e8b5-4506-a061-9a3e4b790066"] ``` --- ``TemplateApply`` can be used to parse and apply a string template in one step: ```wl In[1]:= TemplateApply[ "Best friend of `1` is `2`.", {"John", "Jane"} ] Out[1]= "Best friend of John is Jane." ``` ### Possible Issues (1) Data in the second argument of ``StringTemplate`` takes precedence over arguments in ``TemplateApply`` : ```wl In[1]:= t = StringTemplate["a is `a`", <|"a" -> 1|>]; TemplateApply[t, <|"a" -> 2|>] Out[1]= "a is 1" ``` ### Neat Examples (1) You can deploy a ``StringTemplate`` to the cloud. When you visit the URL, ``TemplateApply`` will render the template on each visit: ```wl In[1]:= t = StringTemplate[ "Hello world now is `now`", <|"now" :> Now|> ]; CloudDeploy[t] Out[1]= CloudObject["https://www.wolframcloud.com/obj/63d10ba3-8e0b-432c-8b20-6595a3282556"] ``` ## See Also * [`FileTemplate`](https://reference.wolfram.com/language/ref/FileTemplate.en.md) * [`XMLTemplate`](https://reference.wolfram.com/language/ref/XMLTemplate.en.md) * [`TemplateApply`](https://reference.wolfram.com/language/ref/TemplateApply.en.md) * [`StringReplace`](https://reference.wolfram.com/language/ref/StringReplace.en.md) * [`StringJoin`](https://reference.wolfram.com/language/ref/StringJoin.en.md) * [`StringRiffle`](https://reference.wolfram.com/language/ref/StringRiffle.en.md) * [`Pluralize`](https://reference.wolfram.com/language/ref/Pluralize.en.md) * [`StringForm`](https://reference.wolfram.com/language/ref/StringForm.en.md) ## Related Guides * [Working with Templates](https://reference.wolfram.com/language/guide/WorkingWithTemplates.en.md) * [String Manipulation](https://reference.wolfram.com/language/guide/StringManipulation.en.md) * [Text Generation](https://reference.wolfram.com/language/guide/TextConstruction.en.md) * [Text Manipulation](https://reference.wolfram.com/language/guide/ProcessingTextualData.en.md) * [Notebook Document Generation](https://reference.wolfram.com/language/guide/DocumentGeneration.en.md) * [External Interpreted Language Interfaces](https://reference.wolfram.com/language/guide/ExternalInterpretedLanguageInterfaces.en.md) * [External Language Interfaces](https://reference.wolfram.com/language/guide/ExternalLanguageInterfaces.en.md) * [LLM-Related Functionality](https://reference.wolfram.com/language/guide/LLMFunctions.en.md) ## Related Workflows * [Create a Webpage with Templates](https://reference.wolfram.com/language/workflow/CreateAWebpageWithTemplates.en.md) ## Related Links * [An Elementary Introduction to the Wolfram Language: String Patterns and Templates](https://www.wolfram.com/language/elementary-introduction/42-string-patterns-and-templates.html) ## History * [Introduced in 2014 (10.0)](https://reference.wolfram.com/language/guide/SummaryOfNewFeaturesIn100.en.md)