String Filters

String filters are where most small presentation fixes happen. They are usually the right tool for display formatting, filename shaping, templated messages, and API-compatible encodings.

Case and whitespace

lower, upper, title, and capitalize normalize casing. trim removes leading and trailing whitespace.

{{ "LOUD TEXT" | lower }}           {# loud text #}
{{ "quiet text" | upper }}          {# QUIET TEXT #}
{{ "article title" | title }}       {# Article Title #}
{{ "hello world" | capitalize }}    {# Hello world #}
{{ "  padded  " | trim }}           {# padded #}

abbreviate

Truncates a string to a maximum length and appends an ellipsis. The length argument includes the ellipsis:

{{ "this is a long sentence." | abbreviate(7) }}    {# this... #}

Useful when you need to keep log messages or notification subjects within a character limit.

replace

Substitutes one or more substrings using a map. Pass regexp=true to use regex patterns in the keys:

{{ "I like %this% and %that%." | replace({'%this%': foo, '%that%': "bar"}) }}

substringBefore, substringAfter, and their Last variants

Extract the portion of a string before or after a delimiter. The Last variants match the final occurrence:

{{ "a.b.c" | substringBefore(".") }}       {# a #}
{{ "a.b.c" | substringAfter(".") }}        {# b.c #}
{{ "a.b.c" | substringBeforeLast(".") }}   {# a.b #}
{{ "a.b.c" | substringAfterLast(".") }}    {# c #}

These are particularly useful for extracting file extensions, path segments, or identifier prefixes from task output values.

slugify

Converts a string into a URL-safe slug:

{{ "Hello World!" | slugify }}    {# hello-world #}

default

Returns a fallback value when the expression is null or empty:

{{ user.phoneNumber | default("No phone number") }}

startsWith

Returns true if the string begins with the given prefix:

{{ "kestra://file.csv" | startsWith("kestra://") }}    {# true #}

endsWith

Returns true if the string ends with the given suffix:

{{ "report.csv" | endsWith(".csv") }}    {# true #}

Encoding and hashing

base64encode and base64decode handle Base64 encoding. urlencode and urldecode percent-encode strings for use in URLs. sha1, sha512, and md5 produce hex-encoded hashes of the corresponding algorithms.

{{ "test" | base64encode }}
{# output: dGVzdA== #}
{{ "dGVzdA==" | base64decode }}
{# output: test #}
{{ "The string ü@foo-bar" | urlencode }}
{# output: The+string+%C3%BC%40foo-bar #}
{{ "The+string+%C3%BC%40foo-bar" | urldecode }}
{# output: The string ü@foo-bar #}
{{ "test" | sha1 }}
{{ "test" | sha512 }}
{{ "test" | md5 }}

string

Coerces any value to its string representation:

{{ 42 | string }}

Use this when chaining filters that expect string input on a value that may arrive as a number or boolean.

escapeChar

Escapes special characters in a string. The type argument controls which style of escaping is applied: single, double, or shell:

{{ "Can't be here" | escapeChar('single') }}
{# output: Can\'t be here #}

Regex filters

regexMatch(regex) returns true if the input contains a substring matching the pattern. regexReplace(regex, replacement) replaces all matching substrings. regexExtract(regex, group) returns the first match or a specific capture group (group defaults to 0; returns null if no match):

{{ "hello world" | regexMatch("w[a-z]+") }}
{# output: true #}
{{ "2024-01-15" | regexReplace("(\\d{4})-(\\d{2})-(\\d{2})", "$3/$2/$1") }}
{# output: 15/01/2024 #}
{{ "order-12345-done" | regexExtract("\\d+") }}
{# output: 12345 #}
{{ "2024-01-15" | regexExtract("(\\d{4})-(\\d{2})-(\\d{2})", 1) }}
{# output: 2024 #}

Worked string filter example

This flow builds a sanitized filename and a display-safe summary from a raw input title:

id: string_filter_example
namespace: company.team


inputs:
  - id: title
    type: STRING
    defaults: "  Quarterly Report: Q1 2025 (FINAL)  "


tasks:
  - id: format_output
    type: io.kestra.plugin.core.log.Log
    message:
      - "Trimmed: {{ inputs.title | trim }}"
      - "Normalized: {{ inputs.title | trim | lower }}"
      - "Slug (for filename): {{ inputs.title | trim | slugify }}"
      - "Abbreviated (for subject line): {{ inputs.title | trim | abbreviate(30) }}"
      - "Prefix check: {{ inputs.title | trim | startsWith('Quarterly') }}"
      - "After colon: {{ inputs.title | trim | substringAfter(':') | trim }}"

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