php - Regex - the difference in \\n and \n -


sorry add "regex explanation" question internet must know reason this. have ran regex through regexbuddy , regex101.com no help.

i came across following regex ("%4d%[^\\n]") while debugging time parsing function. every , receive 'invalid date' error during months of january , june. mocked code recreate happening can't figure out why removing 1 slash fixes it.

<?php $format = '%y/%b/%d'; $random_date_strings = array(     '2015/jan/03',     '1985/feb/13',     '2001/mar/25',     '1948/apr/02',     '1948/may/19',     '2020/jun/22',     '1867/jul/09',     '1901/aug/11',     '1945/sep/21',     '2000/oct/31',     '2009/nov/24',     '2015/dec/02'     );  $year = null; $rest_of_string = null;  echo 'bad regex:'; echo '<br/><br/>'; foreach ($random_date_strings $date_string) {     sscanf($date_string, "%4d%[^\\n]", $year, $rest_of_string);     print_data($date_string, $year, $rest_of_string); }  echo 'good regex:'; echo '<br/><br/>'; foreach ($random_date_strings $date_string) {     sscanf($date_string, "%4d%[^\n]", $year, $rest_of_string);     print_data($date_string, $year, $rest_of_string); }  function print_data($d, $y, $r) {      echo 'date string: ' . $d;     echo '<br/>';     echo 'year: ' . $y;     echo '<br/>';     echo 'rest of string: ' . $r;     echo '<br/>'; } ?>

feel free run locally 2 outputs i'm concerned months of june , january. "%4d%[^\\n]" truncate $rest_of_string /ju , /ja while "%4d%[^\n]" displays rest of string expected (/jan/03 & /jun/22).

here's interpretation of faulty regex:

  • %4d% - 4 digits.
  • [^\\n] - digits in between beginning of string , new line.

can please correct explanation and/or tell me why removing slash gives me result expect?

i don't care how...i need why.

like @lucastrzesniewski pointed out, that's sscanf() syntax, has nothing regex. format explained in sprintf() page.

in pattern "%4d%[^\\n]", 2 \\ translate single backslash character. correct interpretation of "faulty" pattern is:

  • %4d - 4 digits.
  • %[^\\n] - characters not backslash or letter "n"

that's why matches until "n" in "jan" , "jun".

the correct pattern "%4d%[^\n]", \n translates new line character, , it's interpretation is:

  • %4d - 4 digits.
  • %[^\n] - characters not new line

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