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PlantUML Language specification Preprocessing

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Preprocessing

Some preprocessing capabilities are included in PlantUML, and available for all diagrams.

Those functionalities are very similar to the C language preprocessor, except that the special character # has been changed to the exclamation mark !.

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Variable definition [=, ?=]

Although this is not mandatory, we highly suggest that variable names start with a $.

There are three types of data:
  • Integer number (int);
  • String (str) - these must be surrounded by single quote or double quote;
  • JSON (JSON) - either JSON Array or JSON Object or JSON value created by %str2json.
(for JSON variable definition and usage, see more details on Preprocessing-JSON page)

Variables created outside function are global, that is you can access them from everywhere (including from functions). You can emphasize this by using the optional global keyword when defining a variable.

🎉 Copied! 

@startuml
!$a  = 42
!$ab = "foo1"
!$cd = "foo2"
!$ef = $ab + $cd
!$foo = { "name": "John", "age" : 30 }

Alice -> Bob : $a
Alice -> Bob : $ab
Alice -> Bob : $cd
Alice -> Bob : $ef
Alice -> Bob : Do you know **$foo.name** ?
@enduml

You can also assign a value to a variable, only if it is not already defined, with the syntax: !$a ?= "foo"

🎉 Copied! 

@startuml
Alice -> Bob : 1. **$name** should be empty

!$name ?= "Charlie"
Alice -> Bob : 2. **$name** should be Charlie

!$name = "David"
Alice -> Bob : 3. **$name** should be David

!$name ?= "Ethan"
Alice -> Bob : 4. **$name** should be David
@enduml

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Boolean expression

Boolean representation [0 is false]

There is not real boolean type, but PlantUML use this integer convention:

  • Integer 0 means false
  • and any non-null number (as 1) or any string (as "1", or even "0") means true.

[Ref. QA-9702]

Boolean operation and operator [&&, ||, ()]

You can use boolean expression, in the test, with :
  • parenthesis ();
  • and operator &&;
  • or operator ||.

(See next example, within if test.)

Boolean builtin functions [%false(), %true(), %not(<exp>)]

For convenience, you can use those boolean builtin functions:

  • %false()
  • %true()
  • %not(<exp>)

[See also Builtin functions]

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Conditions [!if, !else, !elseif, !endif]

  • You can use expression in condition.
  • else and elseif are also implemented

🎉 Copied! 

@startuml
!$a = 10
!$ijk = "foo"
Alice -> Bob : A
!if ($ijk == "foo") && ($a+10>=4)
Alice -> Bob : yes
!else
Alice -> Bob : This should not appear
!endif
Alice -> Bob : B
@enduml

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While loop [!while, !endwhile]

You can use !while and !endwhile keywords to have repeat loops.

While loop (on Activity diagram)

🎉 Copied! 

@startuml
!procedure $foo($arg)
  :procedure start;
  !while $arg!=0
    !$i=3
    #palegreen:arg=$arg;
    !while $i!=0
      :arg=$arg and i=$i;
      !$i = $i - 1
    !endwhile
    !$arg = $arg - 1
  !endwhile
  :procedure end;
!endprocedure

start
$foo(2)
end
@enduml

[Adapted from QA-10838]

While loop (on Mindmap diagram)

🎉 Copied! 

@startmindmap
!procedure $foo($arg)
  !while $arg!=0
    !$i=3
    **[#palegreen] arg = $arg
    !while $i!=0
      *** i = $i
      !$i = $i - 1
    !endwhile
    !$arg = $arg - 1
  !endwhile
!endprocedure

*:While
Loop;
$foo(2)
@endmindmap

While loop (on Component/Deployment diagram)

🎉 Copied! 

@startuml
!procedure $foo($arg)
  !while $arg!=0
    [Component $arg] as $arg
    !$arg = $arg - 1
  !endwhile
!endprocedure

$foo(4)

1->2
3-->4
@enduml

[Ref. QA-14088]

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Procedure [!procedure, !endprocedure]

  • Procedure names should start with a $
  • Argument names should start with a $
  • Procedures can call other procedures

Example:

🎉 Copied! 

@startuml
!procedure $msg($source, $destination)
  $source --> $destination
!endprocedure

!procedure $init_class($name)
  class $name {
    $addCommonMethod()
  }
!endprocedure


!procedure $addCommonMethod()
  toString()
  hashCode()
!endprocedure


$init_class("foo1")
$init_class("foo2")
$msg("foo1", "foo2")
@enduml

Variables defined in procedures are local. It means that the variable is destroyed when the procedure ends.

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Return function [!function, !endfunction]

A return function does not output any text. It just define a function that you can call:
  • directly in variable definition or in diagram text
  • from other return functions
  • from procedures

  • Function name should start with a $
  • Argument names should start with a $

🎉 Copied! 

@startuml
!function $double($a)
!return $a + $a
!endfunction

Alice -> Bob : The double of 3 is $double(3)
@enduml

It is possible to shorten simple function definition in one line:

🎉 Copied! 

@startuml
!function $double($a) !return $a + $a

Alice -> Bob : The double of 3 is $double(3)
Alice -> Bob : $double("This work also for strings.")
@enduml

As in procedure (void function), variable are local by default (they are destroyed when the function is exited). However, you can access to global variables from function. However, you can use the local keyword to create a local variable if ever a global variable exists with the same name.

🎉 Copied! 

@startuml
!function $dummy()
!local $ijk = "local"
!return "Alice -> Bob : " + $ijk
!endfunction

!global $ijk = "foo"

Alice -> Bob : $ijk
$dummy()
Alice -> Bob : $ijk
@enduml

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Default argument value

In both procedure and return functions, you can define default values for arguments.

🎉 Copied! 

@startuml
!function $inc($value, $step=1)
!return $value + $step
!endfunction

Alice -> Bob : Just one more $inc(3)
Alice -> Bob : Add two to three : $inc(3, 2)
@enduml

Only arguments at the end of the parameter list can have default values.

🎉 Copied! 

@startuml
!procedure defaulttest($x, $y="DefaultY", $z="DefaultZ")
note over Alice
  x = $x
  y = $y
  z = $z
end note
!endprocedure

defaulttest(1, 2, 3)
defaulttest(1, 2)
defaulttest(1)
@enduml

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Unquoted procedure or function [!unquoted]

By default, you have to put quotes when you call a function or a procedure. It is possible to use the unquoted keyword to indicate that a function or a procedure does not require quotes for its arguments.

🎉 Copied! 

@startuml
!unquoted function id($text1, $text2="FOO") !return $text1 + $text2

alice -> bob : id(aa)
alice -> bob : id(ab,cd)
@enduml

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Keywords arguments

Like in Python, you can use keywords arguments :

🎉 Copied! 

@startuml

!unquoted procedure $element($alias, $description="", $label="", $technology="", $size=12, $colour="green")
rectangle $alias as "
<color:$colour><<$alias>></color>
==$label==
//<size:$size>[$technology]</size>//

  $description"
!endprocedure

$element(myalias, "This description is %newline()on several lines", $size=10, $technology="Java")
@enduml

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Including files or URL [!include, !include_many, !include_once]

Use the !include directive to include file in your diagram. Using URL, you can also include file from Internet/Intranet. Protected Internet resources can also be accessed, this is described in URL authentication.

Imagine you have the very same class that appears in many diagrams. Instead of duplicating the description of this class, you can define a file that contains the description.

🎉 Copied! 

@startuml

interface List
List : int size()
List : void clear()
List <|.. ArrayList
@enduml

File List.iuml 

interface List
List : int size()
List : void clear()

The file List.iuml can be included in many diagrams, and any modification in this file will change all diagrams that include it.

You can also put several @startuml/@enduml text block in an included file and then specify which block you want to include adding !0 where 0 is the block number. The !0 notation denotes the first diagram.

For example, if you use !include foo.txt!1, the second @startuml/@enduml block within foo.txt will be included.

You can also put an id to some @startuml/@enduml text block in an included file using @startuml(id=MY_OWN_ID) syntax and then include the block adding !MY_OWN_ID when including the file, so using something like !include foo.txt!MY_OWN_ID.

By default, a file can only be included once. You can use !include_many instead of !include if you want to include some file several times. Note that there is also a !include_once directive that raises an error if a file is included several times.

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Including Subpart [!startsub, !endsub, !includesub]

You can also use !startsub NAME and !endsub to indicate sections of text to include from other files using !includesub. For example:

file1.puml: 

@startuml

A -> A : stuff1
!startsub BASIC
B -> B : stuff2
!endsub
C -> C : stuff3
!startsub BASIC
D -> D : stuff4
!endsub
@enduml

file1.puml would be rendered exactly as if it were: 

@startuml

A -> A : stuff1
B -> B : stuff2
C -> C : stuff3
D -> D : stuff4
@enduml

However, this would also allow you to have another file2.puml like this:

file2.puml 

@startuml

title this contains only B and D
!includesub file1.puml!BASIC
@enduml

This file would be rendered exactly as if: 

@startuml

title this contains only B and D
B -> B : stuff2
D -> D : stuff4
@enduml

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Builtin functions [%]

Some functions are defined by default. Their name starts by %

Name Description Example Return
%chr Return a character from a give Unicode value %chr(65) A
%darken Return a darken color of a given color with some ratio %darken("red", 20) #CC0000
%date Retrieve current date. You can provide an optional format for the date %date("yyyy.MM.dd' at 'HH:mm") current date
You can provide another optional time (on epoch format) %date("YYYY-MM-dd", %now() + 1*24*3600) tomorrow date
%dec2hex Return the hexadecimal string (String) of a decimal value (Int) %dec2hex(12) c
%dirpath Retrieve current dirpath %dirpath() current path
%feature Check if some feature is available in the current PlantUML running version %feature("theme") true
%false Return always false %false() false
%file_exists Check if a file exists on the local filesystem %file_exists("c:/foo/dummy.txt") true if the file exists
%filename Retrieve current filename %filename() current filename
%function_exists Check if a function exists %function_exists("$some_function") true if the function has been defined
%get_variable_value Retrieve some variable value %get_variable_value("$my_variable") the value of the variable
%getenv Retrieve environment variable value %getenv("OS") the value of OS variable
%hex2dec Return the decimal value (Int) of a hexadecimal string (String) %hex2dec("d") or %hex2dec(d) 13
%hsl_color Return the RGBa color from a HSL color %hsl_color(h, s, l) or %hsl_color(h, s, l, a) %hsl_color(120, 100, 50) #00FF00
%intval Convert a String to Int %intval("42") 42
%is_dark Check if a color is a dark one %is_dark("#000000") true
%is_light Check if a color is a light one %is_light("#000000") false
%lighten Return a lighten color of a given color with some ratio %lighten("red", 20) #CC3333
%load_json Load JSON data from local file or external URL %load_json("http://localhost:7778/management/health") JSON data
%lower Return a lowercase string %lower("Hello") hello in that example
%mod Return the remainder of division of two integers (modulo division) %mod(10, 3) 1
%newline Return a newline %newline() a newline
%not Return the logical negation of an expression %not(2+2==4) false in that example
%now Return the current epoch time %now() 1685547132 in that example (when updating the doc.)
%ord Return a Unicode value from a given character %ord("A") 65
%lighten Return a lighten color of a given color with some ratio %lighten("red", 20) #CC3333
%reverse_color Reverse a color using RGB %reverse_color("#FF7700") #0088FF
%reverse_hsluv_color Reverse a color using HSLuv %reverse_hsluv_color("#FF7700") #602800
%set_variable_value Set a global variable %set_variable_value("$my_variable", "some_value") an empty string
%size Return the size of any string or JSON structure %size("foo") 3 in the example
%string Convert an expression to String %string(1 + 2) 3 in the example
%strlen Calculate the length of a String %strlen("foo") 3 in the example
%strpos Search a substring in a string %strpos("abcdef", "ef") 4 (position of ef)
%substr Extract a substring. Takes 2 or 3 arguments %substr("abcdef", 3, 2) "de" in the example
%true Return always true %true() true
%upper Return an uppercase string %upper("Hello") HELLO in that example
%variable_exists Check if a variable exists %variable_exists("$my_variable") true if the variable has been defined exists
%version Return PlantUML current version %version() 1.2020.8 for example
%invoke_procedure() Dynamically invoke a procedure by its name, passing optional arguments to the called procedure. %invoke_procedure("$go", "hello from Bob...") Depends on the invoked procedure
%call_user_func() Invoke a return function by its name with given arguments. %call_user_func("bold", "Hello") Depends on the called function
%splitstr Split a string into an array based on a specified delimiter. %splitstr("abc~def~ghi", "~") ["abc", "def", "ghi"]

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Logging [!log]

You can use !log to add some log output when generating the diagram. This has no impact at all on the diagram itself. However, those logs are printed in the command line's output stream. This could be useful for debug purpose.

🎉 Copied! 

@startuml
!function bold($text)
!$result = "<b>"+ $text +"</b>"
!log Calling bold function with $text. The result is $result
!return $result
!endfunction

Alice -> Bob : This is bold("bold")
Alice -> Bob : This is bold("a second call")
@enduml

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Memory dump [!dump_memory]

You can use !dump_memory to dump the full content of the memory when generating the diagram. An optional string can be put after !dump_memory. This has no impact at all on the diagram itself. This could be useful for debug purpose.

🎉 Copied! 

@startuml
!function $inc($string)
!$val = %intval($string)
!log value is $val
!dump_memory
!return $val+1
!endfunction

Alice -> Bob : 4 $inc("3")
!unused = "foo"
!dump_memory EOF
@enduml

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Assertion [!assert]

You can put assertions in your diagram.

🎉 Copied! 

@startuml
Alice -> Bob : Hello
!assert %strpos("abcdef", "cd")==3 : "This always fails"
@enduml

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Building custom library [!import, !include]

It's possible to package a set of included files into a single .zip or .jar archive. This single zip/jar can then be imported into your diagram using !import directive.

Once the library has been imported, you can !include file from this single zip/jar.

Example: 

@startuml

!import /path/to/customLibrary.zip
' This just adds "customLibrary.zip" in the search path

!include myFolder/myFile.iuml
' Assuming that myFolder/myFile.iuml is located somewhere
' either inside "customLibrary.zip" or on the local filesystem

...

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Search path

You can specify the java property plantuml.include.path in the command line.

For example: 

java -Dplantuml.include.path="c:/mydir" -jar plantuml.jar atest1.txt

Note the this -D option has to put before the -jar option. -D options after the -jar option will be used to define constants within plantuml preprocessor.

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Argument concatenation [##]

It is possible to append text to a macro argument using the ## syntax.

🎉 Copied! 

@startuml
!unquoted procedure COMP_TEXTGENCOMP(name)
[name] << Comp >>
interface Ifc << IfcType >> AS name##Ifc
name##Ifc - [name]
!endprocedure
COMP_TEXTGENCOMP(dummy)
@enduml

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Dynamic invocation [%invoke_procedure(), %call_user_func()]

You can dynamically invoke a procedure using the special %invoke_procedure() procedure. This procedure takes as first argument the name of the actual procedure to be called. The optional following arguments are copied to the called procedure.

For example, you can have:

🎉 Copied! 

@startuml
!procedure $go()
  Bob -> Alice : hello
!endprocedure

!$wrapper = "$go"

%invoke_procedure($wrapper)
@enduml

🎉 Copied! 

@startuml
!procedure $go($txt)
  Bob -> Alice : $txt
!endprocedure

%invoke_procedure("$go", "hello from Bob...")
@enduml

For return functions, you can use the corresponding special function %call_user_func() :

🎉 Copied! 

@startuml
!function bold($text)
!return "<b>"+ $text +"</b>"
!endfunction

Alice -> Bob : %call_user_func("bold", "Hello") there
@enduml

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Evaluation of addition depending of data types [+]

Evaluation of $a + $b depending of type of $a or $b

🎉 Copied! 

@startuml
title
<#LightBlue>|= |=  $a |=  $b |=  <U+0025>string($a + $b)|
<#LightGray>| type | str | str | str (concatenation) |
| example |= "a" |= "b" |= %string("a" + "b") |
<#LightGray>| type | str | int | str (concatenation) |
| ex.|= "a" |=  2  |= %string("a" + 2)   |
<#LightGray>| type | str | int | str (concatenation) |
| ex.|=  1  |= "b" |= %string(1 + "b")   |
<#LightGray>| type | bool | str | str (concatenation) |
| ex.|= <U+0025>true() |= "b" |= %string(%true() + "b") |
<#LightGray>| type | str | bool | str (concatenation) |
| ex.|= "a" |= <U+0025>false() |= %string("a" + %false()) |
<#LightGray>| type |  int  |  int | int (addition of int) |
| ex.|=  1  |=  2  |= %string(1 + 2)     |
<#LightGray>| type |  bool  |  int | int (addition) |
| ex.|= <U+0025>true() |= 2 |= %string(%true() + 2) |
<#LightGray>| type |  int  |  bool | int (addition) |
| ex.|=  1  |= <U+0025>false() |= %string(1 + %false()) |
<#LightGray>| type |  int  |  int | int (addition) |
| ex.|=  1  |=  <U+0025>intval("2")  |= %string(1 + %intval("2")) |
end title
@enduml

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Preprocessing JSON

You can extend the functionality of the current Preprocessing with JSON Preprocessing features:

  • JSON Variable definition
  • Access to JSON data
  • Loop over JSON array

(See more details on Preprocessing-JSON page)

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Including theme [!theme]

Use the !theme directive to change the default theme of your diagram.

🎉 Copied! 

@startuml
!theme spacelab
class Example {
  Theme spacelab
}
@enduml

You will find more information on the dedicated page.

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Migration notes

The current preprocessor is an update from some legacy preprocessor.

Even if some legacy features are still supported with the actual preprocessor, you should not use them any more (they might be removed in some long term future).

  • You should not use !define and !definelong anymore. Use !function, !procedure or variable definition instead.
    • !define should be replaced by return !function
    • !definelong should be replaced by !procedure.
  • !include now allows multiple inclusions : you don't have to use !include_many anymore
  • !include now accepts a URL, so you don't need !includeurl
  • Some features (like %date%) have been replaced by builtin functions (for example %date())
  • When calling a legacy !definelong macro with no arguments, you do have to use parenthesis. You have to use my_own_definelong() because my_own_definelong without parenthesis is not recognized by the new preprocessor.

Please contact us if you have any issues.

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%splitstr builtin function

🎉 Copied! 

@startmindmap
!$list = %splitstr("abc~def~ghi", "~")

* root
!foreach $item in $list
  ** $item
!endfor
@endmindmap

Similar to:

🎉 Copied! 

@startmindmap
* root
!foreach $item in ["abc", "def", "ghi"]
  ** $item
!endfor
@endmindmap

[Ref. QA-15374]

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%splitstr_regex builtin function

🎉 Copied! 

@startmindmap
!$list = %splitstr_regex("AbcDefGhi", "(?=[A-Z])")

* root
!foreach $item in $list
  ** $item
!endfor
@endmindmap

Similar to:

🎉 Copied! 

@startmindmap
* root
!foreach $item in ["Abc", "Def", "Ghi"]
  ** $item
!endfor
@endmindmap

[Ref. QA-18827]

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%get_all_theme builtin function

You can use the %get_all_theme() builtin function to retreive a JSON array of all PlantUML theme.

🎉 Copied! 

@startjson
%get_all_theme()
@endjson

[from version 1.2024.4]

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%get_all_stdlib builtin function

Compact version (only standard library name)

You can use the %get_all_stdlib() builtin function to retreive a JSON array of all PlantUML stdlib names.

🎉 Copied! 

@startjson
%get_all_stdlib()
@endjson

Detailed version (with version and source)

With whatever parameter, you can use %get_all_stdlib(detailed) to retreive a JSON object of all PlantUML stdlib.

🎉 Copied! 

@startjson
%get_all_stdlib(detailed)
@endjson

[from version 1.2024.4]

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%random builtin function

You can use the %random builtin function to retreive a random integer.

Nb param. Input Output
0 %random() returns 0 or 1
1 %random(n) returns an interger between 0 and n - 1
2 %random(min, max) returns an interger between min and max - 1

🎉 Copied! 

@startcreole
| Nb param. | Input | Output |
| 0 | <U+0025>random()      | %random()     |
| 1 | <U+0025>random(5)     | %random(5)    |
| 2 | <U+0025>random(7, 15) | %random(7, 15) |
@endcreole

[from version 1.2024.2]

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