getting emails out of string - regex syntax + preg_match_all

Like this

$pattern = '/[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}\b/i';

Or smaller version :)

$pattern = '/[a-z\d._%+-]+@[a-z\d.-]+\.[a-z]{2,4}\b/i';

When using PCRE regex functions it require to enclose the pattern by delimiters:

PHP Delimiters

Often used delimiters are forward slashes (/), hash signs (#) and tildes (~). The following are all examples of valid delimited patterns.

/foo bar/
#^[^0-9]$#
+php+
%[a-zA-Z0-9_-]%

Then you must correct this line to:

$pattern = '/\b[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}\b/';

$pattern = '#\b[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}\b#';

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