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  1. <?php
  2.  
  3. $r = '~^(?:,|([^,])(?!\\1))+$~';
  4. var_dump(preg_match($r, 'a,,,sd')); // true - because ,,, is allowed
  5. var_dump(preg_match($r, 'asd')); // true - because no repetitions
  6. var_dump(preg_match($r, 'assd')); // false - because double-s
Success #stdin #stdout 0.02s 13112KB
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Standard input is empty
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int(1)
int(1)
int(0)
https://ideone.com/6Q3Wk
language:
PHP (php 7.3.5)
created:
12 years ago
visibility:
public

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