Why Am I Getting 'preg_match(): Compilation failed: invalid range in character class' After My PHP Upgrade?

Invalid Range in Character Class After PHP Upgrade

This error, "preg_match(): Compilation failed: invalid range in character class at offset 20," typically occurs when a PHP upgrade introduces changes to the PCRE engine or the Unicode engine used in your code.

PHP PCRE2 Migration

PHP 7.3 and later versions utilize PCRE2, which introduced several backward-incompatible changes. One such change is the stricter validation of character class patterns.

Hyphens in Character Classes

Previously, you could escape a hyphen (-) and use it anywhere within a character class. However, in PHP 7.3 onwards, you must place the hyphen either at the start or end of the character class only.

Solution

To resolve this error, ensure that hyphens (-) are placed correctly within character classes. If you need to use a hyphen as a character within the class, you must escape it (e.g., -).

Example

// Invalid (in PHP 7.3+)
preg_match("/^[a-z0-9]([0-9a-z_\-\s])+$/i", $subuser);

// Valid (in PHP 7.3+)
preg_match("/^[a-z0-9]([0-9a-z\-_\s])+$/i", $subuser);

Additional Considerations

• PCRE2 features a more strict Unicode engine, which may affect the behavior of some invalid patterns.
• Ensure that your code uses the correct hyphen placement for character classes to avoid compilation errors.
• Refer to the PHP documentation for further details on these changes and compatibility issues.

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