---
id: php-string-slicing
title: "PHP String Slicing"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["substr()", "PHP 문자열 슬라이싱"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.9
created_at: 2026-07-04
updated_at: 2026-07-04
review_reason: ""
merge_history: []
tags: ["php", "programming", "w3schools", "strings", "substr"]
raw_sources: ["https://www.w3schools.com/php/php_string_slicing.asp"]
applied_in: []
github_commit: ""
---

# [[PHP String Slicing]]

## 🎯 한 줄 통찰 (One-line insight)
`substr()`'s length parameter can itself be NEGATIVE — meaning "stop N characters before the end" rather than "take N characters" — so `substr($x, 5, -3)` reads as "start at index 5, and go until you're 3 characters from the end," a dual meaning of the third parameter that requires care since negative start and negative length behave completely differently. [S1]

## 🧠 핵심 개념 (Core concepts)
- **`substr(string, start, length)`** — extracts a substring. [S1]
- **Positive start** — 0-indexed position to begin the slice. [S1]
- **Omitted length** — slices to the end of the string. [S1]
- **Negative start** — counts from the end (-1 is the last character). [S1]
- **Negative length** — stops that many characters BEFORE the end, rather than taking that many characters. [S1]

## 📖 세부 내용 (Details)
- Basic slice: `$x = "Hello World!"; echo substr($x, 6, 5); // "World"`. [S1]
- To the end (no length): `echo substr($x, 6); // "World!"`. [S1]
- Negative start: `echo substr($x, -5, 3); // "Wor" (starting from index -5)`. [S1]
- Negative length: `$x = "Hi, how are you?"; echo substr($x, 5, -3); // "ow are y" (stop 3 chars before the end)`. [S1]

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
- **음수 길이의 의미**: 길이 파라미터가 음수일 경우 "가져올 문자 수"가 아니라 "끝에서부터 생략할 문자 수"로 해석된다는 점이 예제로 명확히 검증됨. [S1]

## 🛠️ 적용 사례 (Applied in summary)
현재 발견된 실제 적용 사례가 없습니다 — 문장 끝 몇 글자를 제외한 나머지를 추출하는 것이 음수 길이 파라미터 활용의 대표 사례다. [S1]

## 💻 코드 패턴 (Code patterns)
Negative length stops before the end of the string (PHP):
```php
$x = "Hi, how are you?";
echo substr($x, 5, -3); // "ow are y"
```

## ✅ 검증 상태 및 신뢰도
- **상태:** draft
- **검증 단계:** conceptual
- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
- **신뢰 점수:** 0.90
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[PHP Tutorial]]
- **관련 개념:** [[PHP String Concatenate]], [[PHP String Escape]], [[PHP Numbers]]
- **참조 맥락:** 문자열 일부 추출 — 이스케이프 문자(Escape) 챕터로 이어짐.

## 📚 출처 (Sources)
- [S1] W3Schools — PHP - Slicing Strings — https://www.w3schools.com/php/php_string_slicing.asp

## 📝 변경 이력 (Change history)
- 2026-07-04: Initial draft synthesized from the W3Schools "PHP - Slicing Strings" page (Astra wiki-curation, P-Reinforce v3.1 format).