Regular expression: match a word of certain length which starts with certain letters
Question
I need a regex which matches a 7 letter word, which starts with 'st' . For example, it should only match 'startin' out of the following: start startin starting
3 answers
solution1
5 2013-05-06 20:48:43
General tips:
The starting symbols are included into the regex directly, eg
st. If the starting characters are special in the sense of regex-syntax (like dots, parentheses, etc.), you need to escape them with a backslash, but it is not needed in your case.After the starting symbols, include character class for the remaining characters of your "word". If you want to allow all characters, use a dot:
.. If you want to allow all non-whitespace characters, use\\S. If you want to allow only (unicode) letters, use\\p{L}. To only allow non-accented latin letters, use[A-Za-z]. There are many possibilities here.Finally, include repetition quantifier for the character class from the previous step. In you case, you need exactly 5 characters after
st, so the repetition quantifier is{5}.If you want only the whole string to match, use
\\Aat the beginning and\\zat the end of your regex. Or include\\bat the beginning/end of your regex to match at the so-called word boundaries (including start/end of the string, whitespace, punctuation). The most powerful alternative (with full control) is the so-called lookahead - I'll leave it out here for the sake of simplicity.
See this tutorial for details. You can just look for specific keywords I've mentioned, eg repetition , character class , unicode , lookahead , etc.
solution2
1 2013-05-06 21:22:57
To match words with non-accent characters that are case insensitive you'll need the i modifier or you'll need to declare both letters at the beginning in both cases.
<?php
$regex = '!\bst[a-z]{5}\b!i';
$words = "start startin starting station Stalker SHOWER Staples Stiffle Steerin StÄbles'";
preg_match_all($regex,$words,$matches);
print_r($matches[0]);
?>
Output
Array
(
[0] => startin
[1] => station
[2] => Stalker
[3] => Staples
[4] => Stiffle
[5] => Steerin
)
With the same output as above, if you didn't use the i modifier you would have to declare more characters:
$regex = '!\b[Ss][Tt][A-Za-z]{5}\b!';
If you want to match Unicode Characters you can do this:
print "<meta charset=\"utf-8\"><body>";
$regex = '!\bst([a-z]|[^u0000-u0080]){5}\b!iu';
$words = "start startin starting station Stalker SHOWER Staples Stiffle Steerin StÄbles'";
preg_match_all($regex,$words,$matches);
print_r($matches[0]);
print "</body>";
Output
Array
(
[0] => startin
[1] => station
[2] => Stalker
[3] => Staples
[4] => Stiffle
[5] => Steerin
[6] => StÄbles //without UTF-8 output it looks like this-> StÃ"bles
)
solution3
0 2013-05-06 20:26:20
preg_match_all('/\bst\w{5}\b/', 'start startin starting', $arr, PREG_PATTERN_ORDER);
更新：根据评论使用前后字边界
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