Working with strings is a key part of PHP programming, and substr() is one of the most useful functions for this. It extracts a portion of a string based on a start position and optional length.

What is substr()?

substr() extracts part of a string. It takes:

  • $string: The original string.
  • $start: The starting index (0-based). Negative values start from the end.
  • $length (optional): Number of characters to extract. Negative values exclude chars from the end.

Syntax

substr(string $string, int $start, ?int $length = null): string

Examples

  1. Basic extraction
echo substr("Hello World", 6); // Output: World

Starts at index 6, returns the rest.

  1. Using length
echo substr("Hello World", 6, 3); // Output: Wor

Extracts 3 characters starting at index 6.

  1. Negative start
echo substr("Hello World", -5); // Output: World

Starts 5 characters from the end.

  1. Negative length
echo substr("Hello World", 0, -6); // Output: Hello

Returns string excluding last 6 characters.

When to Use substr()?

  • Text processing: Extract file extensions, manipulate URLs, or handle user input.
  • Data cleanup: Trim unwanted parts.
  • Custom formatting: Show previews or excerpts.

Final thoughts

substr() is a flexible, essential PHP function for string manipulation. Get comfortable with its parameters to boost your PHP skills.

Quiz

  1. What is the output of:
echo substr("Programming in PHP", 0, 11);
  • A) Programming
  • B) in PHP
  • C) Programmin
  • D) PHP
  1. Which is true about $start in substr()?
  • A) Must be positive
  • B) Can be negative to start from the end
  • C) Determines length
  • D) Is optional

Drop your answers anytime!

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