Twig Code Blocks - Manipulating strings

Overview

To manipulate strings (text) or variables that contain strings, Twig provides a number of built-in filters specifically for working with strings: trimming whitespace, retrieving the length of a string, replacing parts of a string, and so on.

We will review some of the often-used string manipulation filters, and discuss string concatenation (combining two strings into one) and string interpolation (using variables inside strings).

String manipulation filters

You can find all of Twig's built-in filters at https://twig.symfony.com/doc/3.x/filters/index.html. Let's review a few of them.

lower & upper

Converts values to lowercase or uppercase.

Docs

• https://twig.symfony.com/doc/3.x/filters/lower.html 
• https://twig.symfony.com/doc/3.x/filters/upper.html 

Examples

{{ "I LOVE Twig" | lower }}

→  i love twig

{{ "I LOVE Twig" | upper }}

→ I LOVE TWIG

capitalize & title

Capitalises a value (make first character uppercase) or convert to title case (make first character of each word uppercase).

Docs

• https://twig.symfony.com/doc/3.x/fiters/capitalize.html 
• https://twig.symfony.com/doc/3.x/filters/title.html 

Examples

{{ "twig is a template language" | capitalize }}

→  Twig is a template language

{{ "twig is a template language" | title }}

→ Twig Is A Template Language

first & last

Returns the first / last character of a string.

When used with arrays: returns the first / last element of a sequence or mapping.

Docs

• https://twig.symfony.com/doc/3.x/filters/first.html 
• https://twig.symfony.com/doc/3.x/filters/last.html 

Examples

{{ "twig is a template language" | first }}

→ t

{{ "twig is a template language" | last }}

→ e

length

Returns the number of characters in a string, or the number of elements in a sequence or mapping.

This filter is used very often in loops, when you want to perform an operation on every element.

Docs

• https://twig.symfony.com/doc/3.x/filters/length.html 

Examples

{{ "twig is a template language" | length }}

→ 27

trim

Removes characters (typically whitespace) from the left or right side of a string.

Arguments

• First argument (optional): character(s) to strip. Defaults to whitespace.
• Second argument (optional): "left" or "right". Defaults to both sides.

Docs

• https://twig.symfony.com/doc/3.x/filters/trim.html

Examples

{% set message = "       Long-range scanners have detected a subspace anomaly._" %}
{{ message | trim }}
{{ message | trim('right') }}
{{ message | trim('_') }}

Output:

Long-range scanners have detected a subspace anomaly._
      Long-range scanners have detected a subspace anomaly._
      Long-range scanners have detected a subspace anomaly.

Explanation:

• Example 1: whitespace (default) trimmed from both sides (default)
• Example 2: whitespace (default) trimmed from the right side
• Example 3: "_" trimmed from both sides (default)

join

Combines elements of a sequence into one string.

Arguments

If no arguments are given, all values "stick together" without separation.

• First optional argument: string to use as a separator.
• Second optional argument: spacer string to use before the last element.

Docs

https://twig.symfony.com/doc/3.x/filters/join.html 

Examples

{%
 set cities = [ 'Luanda', 'Wellington', 'La Paz', 'Zagreb', 'New Delhi' ]
%}
joined without arguments: 
{{ cities | join }}
joined with one single-character argument: 
{{ cities | join('-') }}
joined with one string argument: 
{{ cities | join(' - ') }}
joined with two arguments:  
{{ cities | join(', ', ', and ') }}

Output:

joined without arguments: 
LuandaWellingtonLa PazZagrebNew Delhi
joined with one single-character argument: 
Luanda-Wellington-La Paz-Zagreb-New Delhi
joined with one string argument: 
Luanda - Wellington - La Paz - Zagreb - New Delhi
joined with two arguments:  
Luanda, Wellington, La Paz, Zagreb, and New Delhi

The last example with two arguments may need a short explanation:

• first argument: ', ' (a string consisting of a comma and a space)
• second argument: ', and ' (string consisting of a comma, a space, the word "and", and another space), used as the last separator.

replace

Replaces placeholders in a string. Anything can be defined as a placeholder.

Docs

• https://twig.symfony.com/doc/3.x/filters/replace.html 

Examples

{%
 set message = "You have %old old and %new new messages."
%}
{%
 set values = {
   '%old': 0,
   '%new': 42
 }
%}
{{ message | replace(values)}}
---
The same operation written in a shorter way:
{{ "You have %old old and %new new messages." | replace({'%old': 0, '%new': 42}) }}

Output:

You have 0 old and 42 new messages.
---
The same operation written in a shorter way:
You have 0 old and 42 new messages.

Explanation:

The placeholder can be anything you want. You can replace all letters "e" with "o" if you'd like, or use $NUM_OLD instead of %old.

You can replace any string you want, be careful with your placeholders: they must be unique enough to ensure that Twig doesn't replace characters you did not intend to replace.

Here's an example of a badly chosen placeholder:

{# Example of a BADLY CHOSEN PLACEHOLDER: #}
{% set message = "This item from Professor Xavier costs X gold coins." %}
{% set price = { 'X': 1000} %}
{{ message | replace(price) }}

Output:

This item from Professor 1000avier costs 1000 gold coins.

A quick solution would be to use a placeholder like $X or %X or XCOINS or something else that is guaranteed to be unique inside the string.

date

Formats a date according to a given PHP date format.

Docs

• https://twig.symfony.com/doc/3.x/filters/date.html

Arguments

• format (optional): the date format to use (defaults to F j, Y H:i)
• timezone (optional): the timezone to use

Examples

Default date format: {{ now | date }}
Day-Month-Year format: {{ now | date("d/m/Y") }}
Year-Month-Day format: {{ now | date("Y-m-d") }}

Output:

October 22, 2024 11:32
22/10/2024
2024-10-22

Explanation:

• If no date format is provided, the default F j, Y H:i format is used.

Please refer to Twig's date docs for more info and examples, and to the PHP date format docs to learn about all the other formatting options for date/time components.

String concatenation

Putting two strings together is called string concatenation.

In PHP you would use the dot operator (.) to concatenate strings; Twig provides the tilde operator (~)

PHP Example

$first_name = 'Roberto';
$last_name = 'Diaz';
$full_name = $first_name . ' ' . $last_name;
print $full_name;

Output:

Roberto Diaz

Twig Example

{% set first_name = 'Roberto' %}
{% set last_name = 'Diaz' %}
{% set full_name = first_name ~ ' ' ~ last_name %}
{{ full_name }}

Output:

Roberto Diaz

Conclusion

Use the tilde operator (~) to concatenate strings in Twig.

String interpolation

String interpolation is the process of embedding strings inside other strings.

PHP

In PHP,  there are a few different methods for string interpolation, including:

$output = "Error encountered: $error_message.";
// or
$output = "Error encountered: {$error_message}.";

Twig

{% set output = "Error encountered: #{error_message}." %}

Conclusion

Use the #{expression} notation for each variable you want to embed inside a string.

Warning

In PHP and Twig, string interpolation is only supported in double-quoted strings ("...").

In both languages single-quoted strings ('...') are always printed as-is, and never evaluated for embedded variables or other special content.