trim_start

This page explains how to use the trim_start function in APL.

The trim_start function removes all leading occurrences of specified characters from a string. Use this function to clean log data, remove leading whitespace or special characters, or standardize string formats by removing unwanted prefixes.

For users of other query languages

If you come from other query languages, this section explains how to adjust your existing queries to achieve the same results in APL.

Splunk SPL users

In Splunk SPL, you use ltrim for leading whitespace. APL’s trim_start provides more flexibility with custom character sets.

Splunk example

| eval cleaned=ltrim(field)

['sample-http-logs']
| extend cleaned = trim_start(' ', field)

ANSI SQL users

In ANSI SQL, you use LTRIM for leading characters. APL’s trim_start provides similar functionality.

SQL example

SELECT LTRIM(field) AS cleaned FROM logs;

['sample-http-logs']
| extend cleaned = trim_start(' ', field)

Usage

Syntax

trim_start(cutset, text)

Parameters

Name	Type	Required	Description
cutset	string	Yes	A string containing characters to remove from the beginning.
text	string	Yes	The source string to trim.

Returns

Returns the source string with all leading characters in the cutset removed.

Use case examples

Log analysis

Remove leading slashes from URIs for consistent path analysis.

Query

['sample-http-logs']
| extend cleaned_uri = trim_start('/', uri)
| summarize request_count = count() by cleaned_uri, method
| sort by request_count desc
| limit 10

Run in Playground

Output

cleaned_uri	method	request_count
api/users	GET	2341
api/orders	POST	1987
api/products	GET	1654

This query removes leading slashes from URIs, standardizing path formats for consistent grouping and analysis.

OpenTelemetry traces

Remove environment prefixes from service names for cross-environment analysis.

Query

['otel-demo-traces']
| extend cleaned_service = trim_start('prod-dev-staging-', ['service.name'])
| summarize span_count = count() by cleaned_service
| sort by span_count desc
| limit 10

Run in Playground

Output

cleaned_service	span_count
frontend	4532
checkout	3421
cart	2987

This query removes common environment prefix characters from service names, enabling aggregation across different deployment environments.

Security logs

Remove leading special characters from URIs to detect obfuscated attack patterns.

Query

['sample-http-logs']
| extend cleaned_uri = trim_start('./', uri)
| extend is_traversal = indexof(cleaned_uri, '..') >= 0
| where is_traversal
| project _time, uri, cleaned_uri, is_traversal, id, ['geo.country']
| limit 10

Run in Playground

Output

_time	uri	cleaned_uri	is_traversal	id	geo.country
2024-11-06T10:00:00Z	./../../etc/passwd	../../etc/passwd	true	user123	Unknown

This query cleans leading dot and slash characters to reveal path traversal patterns that might be obfuscated with leading characters.

List of related functions

• trim_end: Removes trailing characters. Use this to trim from the end instead of the beginning.
• trim: Removes both leading and trailing characters. Use this when you need to clean both ends.
• trim_start_regex: Removes leading matches using regex. Use this for pattern-based trimming.
• replace_string: Replaces strings. Use this when you need to remove characters from anywhere, not just the start.