Strings in BoxLang/Java are immutable! Remember that well!

In BoxLang, strings are a type of variable that is used to store collections of letters and numbers. Usually defined within single or double quotes ( ' or " ). Some simple strings would be "hello" or "This sentence is a string!". Strings can be anything from "", the empty string, to long sets of text.

The underlying type for a string in BoxLang is the Java String, which is immutable, meaning it can never change. Thus, a new string object is always created when concatenating strings together. This is a warning that if you do many string concatenations, you will have to use a Java data type to accelerate the concatenations (String Builders).

Character Extractions

You can reference characters in a string stream via their position in the string using array syntax: varname[ position ]. Please note that string and array positions in BoxLang start at 1 and not 0.

name = "luis";
writeoutput( name[ 1 ] ) => will produce l

You can use negative indices to get characters from the end backward:

name = "luis";
writeoutput( name[ -1 ] ) => will produce s

Character Extractions by Range

BoxLang also supports extraction as ranges using the following array syntax:

array[ start:stop:step ]

Which is extremely useful for doing character extractions in ranges

 data = "Hello BoxLang. You Rock!";

 writeOutput( data[ 1 ] ) // Returns H
 writeOutput( data[ -3 ] ) // Returns c
 writeOutput( data[ 4:10:2 ] ) // Returns l FL
 writeOutput( data[ 4:12 ] ) // Returns lo BoxLang
 writeOutput( data[ -10:-4:2]) // Returns o o

Common String Functions

You can find all the available string functions here: Below are some common ones that are handy to memorize:


Call len() on a string to get back the number of characters in the string. For instance Len( "Hello ") would give you back 6 (notice the trailing space is counted). You can also use member functions: a.len().

message = "Hola Luis"
writeOutput( message.len() )

if( len( message ) ){


Trim, LTrim, RTrim

TheTrim function removes leading and trailing spaces and controls characters from a string. You can also use the ltrim() to do left trimming and rtrim() to do right trimming.

For instance, Trim("Hello ") would give you back Hello (notice the trailing space is removed). Combine this with Len for example Len( Trim( "Hello ") ) and you would get back 5. You can also use member functions:


Replace, ReplaceNoCase, REReplace, REReplaceNoCase

The Replace instruction replaces occurrences of substring1 in a string with substring2, in a specified scope. The search is case-sensitive and the scoped default is one. If you would like the searches to be case-insensitive just use the noCase() suffix.

For instance, Replace("Hello", "l", "") would give you back Helo after replacing the first occurrence of l, or Replace("Good Morning!", "o", "e", "All") would give you Geed Merning!

REReplace(), REReplaceNoCase() are the same functions but using regular expressions:

reReplace( "test 123!", "[^a-z0-9]", "", "ALL" )
reReplace( "123abc456", "[0-9]+([a-z]+)[0-9]+", "\1" )


RemoveChars will remove characters from a string. For instance, RemoveChars("hello bob", 2, 5) would give you back hbob.


The mid function extracts a substring from a string. For instance, I could call Mid("Welcome to BoxLang Jumpstart", 4, 12) and it would give you back: come to BoxLang.

s = "20001122"
writedump( mid( s, 5, 2 ) )
// You can also use character extraction
writedump( s[ 5:6 ] )


Another great function is listToArray() which can take any string and convert it to an array according to a delimiter, empty fields, and even multi-character delimiters. The default delimiter is a comma ,, but you can use any one or a combination of characters.

a = "luis,majano,lucas,alexia,veronica";
myArray = a.listToArray();

// Multi-character delimiter
list = "boxlang,php,|test,java,|sql";
getArray = listToArray(list,",|",false,true);
someJSON = serializeJSON(getArray);

Combining Strings

Combining and interpolating strings is part of any programming language and an integral part. We can do both by building upon some language operators. If you have two or more strings, you can concatenate them by using the & operator:

name = "Luis";
a = "Hello " & name & " how are you today?";

You can also concatenate and assign using the &= operator. Please check out the operators section for more on string assignment operators.

Interpolating Strings

Interpolating is where we stick a string within another string. In BoxLang, we use the # hashes to output a variable to the stream in context. This means we can interpolate into any string:

name = "luis";
welcome = "Good morning #name#, how are you today?";
writeoutput( welcome );

That's it! If you surround any simple variable with hashes, BoxLang will interpret the variable. Now try this with a complex variable and see what happens:

complex = [1,2,3];
welcome = "Good morning #complex#, how are you today (#now()#)?";
writeoutput( welcome );

Please note that anything between hashes is interpreted as an expression in BoxLang.


BoxLang also will try to automatically infer and auto-cast strings for you. However, there is a built-in function called toString() which can be used to try to convert any value to a string.

s = {
    "a": "1",
writeOutput( toString(s) )
writeOutput( s.toString() )

number = 42222.222
writedump( number.toString() )

Last updated


Copyright & Register Trademark by Ortus Solutions, Corp & Ortus Software, LLC