diff --git a/format.md b/format.md
index 76e12b8a..e5ed1526 100644
--- a/format.md
+++ b/format.md
@@ -24,6 +24,20 @@ TODOC: coupled formula using ${some-formula:some-index-formula} notation
 
 
 
+## Filter
+
+We can use builtin filter at substitution time, using the `${formula/filter}` syntax.
+
+Valid filters:
+* uppercase
+* lowercase
+* regexp: escape for regexp pattern
+* shellarg: escape for a shell argument
+
+
+
+
+
 # References
 
 ## Top level
diff --git a/lib/spellcast.js b/lib/spellcast.js
index 01686114..37f3d61d 100644
--- a/lib/spellcast.js
+++ b/lib/spellcast.js
@@ -1006,10 +1006,14 @@ spellcast.Book.prototype.castTransmute = function castTransmute( transmute , cas
 
 spellcast.Book.prototype.variableSubstitution = function variableSubstitution( input )
 {
-	var output , self = this ;
+	var i , filters , output , self = this ;
 	
-	output = input.replace( /\$\{([0-9a-zA-Z_-]+)(:([0-9a-zA-Z_-]+))?\}/g , function() {
-		var index , thirdParty , substitute = self.formula[ arguments[ 1 ] ] ;
+	output = input.replace( /\$\{([0-9a-zA-Z_-]+)(:([0-9a-zA-Z_-]+))?([\\\/0-9a-zA-Z_-]*)?\}/g , function() {
+	//output = input.replace( /\$\{([0-9a-zA-Z_-]+)(:([0-9a-zA-Z_-]+))?\}/g , function() {
+		
+		//console.log( 'arguments:' , arguments ) ;
+		
+		var index , value , thirdParty , substitute = self.formula[ arguments[ 1 ] ] ;
 		
 		if ( substitute === undefined ) { return '' ; }
 		
@@ -1036,7 +1040,26 @@ spellcast.Book.prototype.variableSubstitution = function variableSubstitution( i
 			index = substitute.index ;
 		}
 		
-		return substitute[ index ] ;
+		value = substitute[ index ] ;
+		
+		// Filters
+		if ( arguments[ 4 ] )
+		{
+			filters = arguments[ 4 ].split( '/' ) ;
+			filters.shift() ;
+			
+			for ( i = 0 ; i < filters.length ; i ++ )
+			{
+				//console.log( "filter #" + i + ":" , filters[ i ] ) ;
+				
+				if ( spellcast.filter[ filters[ i ] ] )
+				{
+					value = spellcast.filter[ filters[ i ] ]( value ) ;
+				}
+			}
+		}
+		
+		return value ;
 	} ) ;
 	
 	return output ;
@@ -1044,6 +1067,19 @@ spellcast.Book.prototype.variableSubstitution = function variableSubstitution( i
 
 
 
+spellcast.filter = {
+	'uppercase': function uppercase( str ) { return str.toUpperCase() ; } ,
+	'lowercase': function lowercase( str ) { return str.toLowerCase() ; } ,
+	'regexp': function escapeRegExp( str ) {
+		return str.replace( /([.*+?^${}()|\[\]\/\\])/g , "\\$1" ) ;
+	} ,
+	'shellarg' : function escapeShellArg( str ) {
+		return '\'' + str.replace( /\'/g , "'\\''" ) + '\'' ;
+	}
+} ;
+
+
+
 spellcast.Book.prototype.argsVariableSubstitution = function argsVariableSubstitution( inArgs )
 {
 	var key , args = {} ;
@@ -1059,15 +1095,6 @@ spellcast.Book.prototype.argsVariableSubstitution = function argsVariableSubstit
 
 
 
-spellcast.filter = {} ;
-
-spellcast.filter['regexp-escape'] = function regexpEscape( str )
-{
-	return str.replace( /[-\/\\^$*+?.()|[\]{}]/g, '\\$&' ) ;
-} ;
-
-
-
 
 
 			/* Makefile builder */
diff --git a/test/spellbook b/test/spellbook
index 25c4b497..61799d3a 100644
--- a/test/spellbook
+++ b/test/spellbook
@@ -2,8 +2,10 @@
 formula
 	alert:bob
 	blah:blih
+	allcaps:FUUU
 	list:one,two,three
 	list-fr:un,deux,trois
+	version:0.1.2
 
 
 
@@ -20,6 +22,12 @@ formula
 	scroll
 		echo ${alert} ${blah}${blah} ${list}
 
+.kawarimi-filter
+	scroll
+		echo ${version/regexp/shellarg}
+		echo ${alert/uppercase}
+		echo ${allcaps/lowercase}
+
 .foreach
 	foreach list
 		scroll
diff --git a/test/spellcast-test.js b/test/spellcast-test.js
index c7aa4bbd..e25a086a 100644
--- a/test/spellcast-test.js
+++ b/test/spellcast-test.js
@@ -78,7 +78,7 @@ function getFizzledLog( spell )
 
 
 
-describe( "Formula" , function() {
+describe( "Formula & variable substitution" , function() {
 	
 	it( "should be parsed into list of string, with an additionnal property 'index' equals to 0" , function() {
 		var book = new spellcast.Book( fs.readFileSync( 'spellbook' ).toString() ) ;
@@ -86,52 +86,67 @@ describe( "Formula" , function() {
 		expect( book.formula.alert ).to.be.eql( [ 'bob' ] ) ;
 		expect( book.formula.list ).to.be.eql( [ 'one' , 'two' , 'three' ] ) ;
 	} ) ;
-} ) ;
-
-
-
-describe( "'scroll' block" , function() {
 	
-	it( "should echoing echo" , function( done ) {
+	it( "should substitute variable (aka formula) accordingly in 'scroll' block" , function( done ) {
 		
 		cleanup( function() {
 			
 			var book = new spellcast.Book( fs.readFileSync( 'spellbook' ).toString() ) ;
 			
-			book.cast( 'echo' , function( error )
+			book.cast( 'kawarimi' , function( error )
 			{
 				expect( error ).not.ok() ;
-				expect( getCastedLog( 'echo' ) ).to.be( 'echo\n' ) ;
+				expect( getCastedLog( 'kawarimi' ) ).to.be( 'bob blihblih one\n' ) ;
 				done() ;
 			} ) ;
 		} ) ;
 	} ) ;
 	
-	it( "should echoing delayed-echo after one second" , function( done ) {
+	it( "should substitute variable (aka formula) using filters" , function( done ) {
 		
 		cleanup( function() {
 			
 			var book = new spellcast.Book( fs.readFileSync( 'spellbook' ).toString() ) ;
 			
-			book.cast( 'delayed-echo' , function( error )
+			book.cast( 'kawarimi-filter' , function( error )
 			{
 				expect( error ).not.ok() ;
-				expect( getCastedLog( 'delayed-echo' ) ).to.be( 'delayed-echo\n' ) ;
+				expect( getCastedLog( 'kawarimi-filter' ) ).to.be( '0\\.1\\.2\nBOB\nfuuu\n' ) ;
 				done() ;
 			} ) ;
 		} ) ;
 	} ) ;
+} ) ;
+
+
+
+describe( "'scroll' block" , function() {
 	
-	it( "should substitute variable (aka formula) accordingly in 'scroll' block" , function( done ) {
+	it( "should echoing echo" , function( done ) {
 		
 		cleanup( function() {
 			
 			var book = new spellcast.Book( fs.readFileSync( 'spellbook' ).toString() ) ;
 			
-			book.cast( 'kawarimi' , function( error )
+			book.cast( 'echo' , function( error )
 			{
 				expect( error ).not.ok() ;
-				expect( getCastedLog( 'kawarimi' ) ).to.be( 'bob blihblih one\n' ) ;
+				expect( getCastedLog( 'echo' ) ).to.be( 'echo\n' ) ;
+				done() ;
+			} ) ;
+		} ) ;
+	} ) ;
+	
+	it( "should echoing delayed-echo after one second" , function( done ) {
+		
+		cleanup( function() {
+			
+			var book = new spellcast.Book( fs.readFileSync( 'spellbook' ).toString() ) ;
+			
+			book.cast( 'delayed-echo' , function( error )
+			{
+				expect( error ).not.ok() ;
+				expect( getCastedLog( 'delayed-echo' ) ).to.be( 'delayed-echo\n' ) ;
 				done() ;
 			} ) ;
 		} ) ;