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33. File I/O

Reading and writing files.

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PHP offers both simple helpers like file_get_contents() and file_put_contents(), and lower-level stream functions fopen()/fread()/fwrite()/fclose() for finer control over large files. File existence and permissions can be checked with file_exists() and is_writable().

When working with user-uploaded paths or file names, always validate and sanitize them to prevent path traversal attacks (e.g., '../../etc/passwd').

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Check your understanding

1. Which function reads an entire file into a string in one call?
fopen()file_get_contents()readfile_string()fscanf()
2. What risk arises from using unsanitized user input as a file path?
Slower performancePath traversal attacksMemory leaksType coercion errors

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