GetPot Dollar Bracket Language.
The dollar bracket language allows a variety of operations on variables, numbers and strings inside a configuration file. For the programmer that reads the configuration file, it is completely indifferent if the file was written using dollar bracket language or not. The user on the other hand, can decide how much of its features he wants to use. The programmer who reads the information from the GetPot objects still always operates with the same ease. One goal if GetPot is also to establish a standardization of this configuration file language. This way many applications can offer compfortable configuration files, and users don't not have to learn for each application another language. One means in order to achieve this is a massive porting to different programming languages such as C++, Java, Python, and Ruby. 
 
# -*- getpot -*- GetPot mode activation for emacs 
# Example input file to be parsed by 'GetPot':
#-------------------------------------------------------------------------------
# PURPOSE:
#           
# Demonstrationof the $-Bracket Language in GetPot.  
# (C) 2002 Frank R. Schaefer                     License Terms: GNU GPL
################################################################################
 
#-------------------------------------------------------------------------------
# (1) variable replacement -----------------------------------------------------
#-------------------------------------------------------------------------------
name = GetPot

[${name}] # meaning: [GetPot]
address = getpot.sourceforge.net
[]
info0 = ${GetPot/address}

[1.2] # advanced variable replacement ------------------------------------------
[Philosophy]
   boss       = 'Dr. Frederique Mouillard'
   members    = 4
   professors = 3
[Mechanical-Engineering]
   boss       = Dr.\ Frieda\ LaBlonde
   members    = 24
   professors = 5

[]
x1 = Mechanical-Engineering
x2 = Philosophy
[1.2]
info0 = '${${x1}/boss}: ${${x1}/professors}/${${x1}/members}'
info1 = '${${x2}/boss}: ${${x2}/professors}/${${x2}/members}'


[1.3] # recursive replacements -------------------------------------------------
#      1.3.1 simple replacements
car            = Citroen-2CV
ground-vehicle = car
vehicle        = ground-vehicle
object         = vehicle
# ${object}         --> vehicle
# ${vehicle}        --> ground-vehicle
# ${ground-vehicle} --> car
# ${car}            --> Citroen-2CV

# note that even variable names can be composed of ${ } expressions
variable = info0
${variable} = '${${ ${ ${object}}}}'

#      1.3.2 conglomerate variable names
[Citroen-2CV]
        [./wheels]
                [./front]
                        [./right]
                        radius = 30 # [cm]

[1.3]
part      = wheels
attribute = radius
position  = front/right

variable  = info1
${variable} = '${${${${${object}}}}/${part}/${position}/${attribute}}'

[1.4] # dictionaries -----------------------------------------------------------

[Nicknames]
        BMW         = Beamer
        Mercedez    = Grandpa\'s\ Slide
        Volkswagen  = Beetle
        Citroen-2CV = Deuche
[1.4]
info0 = '${Nicknames/${1.3/info0}}'
my-car = Mercedez
info1 = '${Nicknames/${1.4/my-car}}'

#-------------------------------------------------------------------------------
# (2) string expressions -------------------------------------------------------
#-------------------------------------------------------------------------------
[2.1] # pure strings -----------------------------------------------------------
info0 = ${:even expressions like ${my-car} are left as they are}
info1 = ${:\\-ing (backslashing) works still the same way}
info2 = ${:backslashes allow one to have spaces w/o quotes}

[2.2] # concatination ----------------------------------------------------------
info0  = ${& simple concatination without whitespaces results in a mess}
info1 =  '${& ${:In France, the } ${1.3/info0} 
          ${: is called \'La } ${Nicknames/${1.3/info0}} \'}
         '

[2.3] # replacement ------------------------------------------------------------
info0 = 'We spell your name \'${<-> Phillip Ph F}\''
info1 = 'The ${<-> ${Nicknames/Volkswagen} ee ea}s'
car = Nicknames/Citroen-2CV
info2 = 'I switched from ${${car}} to ${${<-> ${car} Citroen-2CV Volkswagen}}'

#-------------------------------------------------------------------------------
# (3) numeric expressions ------------------------------------------------------
#-------------------------------------------------------------------------------
[3.1] # basics -----------------------------------------------------------------
info0 = ${+ 1 1}
x = 4699 y = 14 z = 4
# don't forget to glue the minus sign to negative numbers
info1 = ${+ ${x} ${y} -2}

info2 = ${- 10 1}
info3 = ${- ${x} ${y} -2}

info4 = '${* 12 12}'
info5 = '${* 2 2 ${z}}'

info6 = '${/ 12 6}'
info7 = '${/ 144 12 3 2}'

[3.2] # power expressions ------------------------------------------------------
info0 = '${^ 2 16}'
info1 = '${^ 2 2 2 2}'  # ((2^2 = 4)^2 = 16)^2 = 256


[3.3] # comparisons ------------------------------------------------------------
info0 = ${== 1 2}
info1 = ${== Deuche ${${2.3/car}}}
info2 = ${== 1.0 1.000}
info3 = '${>= 3.14 12} but ${>= 3.14 0.0} and ${>= 3.14 3.140000}'
info4 = '${< 12 3.14} but ${< 3.14 3.141} and ${> Berta Vladimir}'
info5 = '${> 12 3.14} but ${> 3.14 3.141} and ${> Zeppelin Alberta}'

# which one is right ? ---------------------------------------------------------
# comparison operator return number of first matching in list
info6 = 'The real name for 'Deuche' is number ${== Deuche
                                                   ${Nicknames/Volkswagen}
                                                   ${Nicknames/Mercedez}
                                                   ${Nicknames/Citroen-2CV}
                                                   ${Nicknames/BMW}}'

info7 = 'The first element less than 2 is element number ${> 2 10 1001 3 6 1 9 -10}'

[3.4] # conditions -------------------------------------------------------------
guess = Citroen-2CV
info0 = 'Your guess was ${? ${== Citroen-2CV ${guess}} right wrong}'
x = 12 y = 14
info1 = 'x (=${x}) is ${?${> ${x} ${y}} greater less} than y (=${y})'
[msg]
english   = 'Star Wars'
francais  = 'La Guerre des Etoiles'
espagnol  = 'Las Guerras De la Estrella'
italiano  = 'Le Guerre Della Stella'
deutsch   = 'Krieg der Beruehmten'
portugues = 'As Guerras Da Estrela'

[3.4] # choices 
domain = .fr
info2 = '${?? ${== ${domain} .de .uk .fr .es .it .pt} 
              ${msg/deutsch}
              ${msg/english}
              ${msg/francais}
              ${msg/espagnol}
              ${msg/italiano}
              ${msg/portugues}}'

[3.5] # vector/string subscription ---------------------------------------------
#       (note, that '-1' stands for end of array)
# string subscription ${@:
info0 = '${@: Wasserkraftwerkinstallationsunternehmenspruefstelle 6 10}'
info1 = '${@: Wasserkraftwerkinstallationsunternehmenspruefstelle 4}'
info2 = '${@: Wasserkraftwerkinstallationsunternehmenspruefstelle 40 -1}'
info3 = '${@: Wasserkraftwerkinstallationsunternehmenspruefstelle 0 5}'

my-vector = 'Cordoba Madrid Buenos-Aires Kairo Moskow Heidelberg 
             Grenoble Marseille Disneyland'

# vector subscription ${@:
info4 = ${@ my-vector  4  -1} # element 4 until end
info5 = ${@ info4  3  4}      # element 3 and 4
info6 = ${@ info4  0  3}      # element 0 until 3 (3 included)
info7 = ${@ info4  4}         # element 4


[3.6] # macro evalutation ------------------------------------------------------
# Note that the accuracy is horrible :-) !
# approximation of a sinus (defined as a pure string):
#     sin(x) = x -1/6 x^3 + 1/120 x^5 -1/5400 x^7 .... 
x2  = ${: ${* ${x} ${x}}}
x4  = ${: ${* ${!x2} ${!x2}}}
x6  = ${: ${* ${!x4} ${!x2}}}
sin = ${: ${* ${x} 
               ${+ 1       
                   ${/ ${!x2} -6}  
                   ${/ ${!x4} 120}   
                   ${/ ${!x6} -5040}
               }            
           }
       }

convert = ${/ 3.14 180.0}  # [degree] -> [rad]

x = ${* 30 ${convert}}   
info0 = ${!sin}

x = ${* 60 ${convert}}   
info1 = ${!sin}