In three minutes, you will learn about PHP regular metacharacters

The power of regular expressions comes from their ability to select and repeat within patterns. Some characters are given special meanings so that they no longer simply represent themselves. These encoded characters with special meanings in the pattern are called metacharacters. Let’s take a look at the commonly used metacharacters.

Commonly used metacharacters for regular expressions in PHP

(1) \dMatch any decimal number, which is equivalent to [0-9];

(2) \D can match any character other than decimal number, etc. Priced at [^0-9];

(3) \s matches any whitespace character, such as form feed (\f ), newline character (\n), tab character (\t), vertical tab character (\v);

(4) \S matches any character except whitespace characters;

(5) \w matches any number, letter or underscore;

(6) \W matches any character except numbers, letters or underscores;

(7) {n} means that the previous character appears exactly n times;

(8) {n,} means that the previous character appears no less than n times;

(9) {n,m} means that the previous character appears no less than n times and at most m times;

(10) ^ or \A matches the starting position of the string;

(11) | Matches two or more patterns (just match one of them);

(12) [] Matches the ones in square brackets Any character;

(13) . matches all characters except newline characters (\n);

(14) () Treat the brackets as a whole to get the contents (in our regular expressions, we can use parentheses to enclose a certain paragraph. After the parentheses, we can use \\Numbers represent the content matched by the regular expression in parentheses);

(15) \.matches.;

(16 ) Matches the preceding character one or more times;

(17) ? Matches the preceding character zero or one time;

(18) . Matches all characters;

(19) ^\t Matches those starting with a tab character;

(20) [^] matches any character except the characters in square brackets;

(21) p.p can match any character in the middle, . can match any character;

(22) * means that the preceding atom can appear any number of times;

(23) $ means that the preceding atom Only characters ending in atoms can be matched, such as w{2}$ www wwww wwwwwwwWhen this happens, we will only match the last two ww

It should be noted that: is used in conjunction with greedy matching by default (try to match the longest string); .*Added a? after it can solve the problem of greedy matching. It becomes lazy matching (try to match the shortest string).

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