Regular expression implementation steps
This time I will introduce to you the syntax of regular expression. Regular expression is a text pattern, including ordinary characters and special characters. The regular pattern describes how to search for text. To match one or more strings.
1. Basic syntax of regular expressions
Two special symbols '^' and '$'. Their function is to indicate the beginning and end of a string respectively. Examples are as follows:
"^The": indicates all strings starting with "The" ("There", "The cat", etc.);
"of despair$": indicates all strings starting with "of" A string ending in despair";
"^abc$": indicates a string that starts and ends with "abc" - haha, only "abc" itself;
"notice": indicates any string containing " notice" string.
Like the last example, if you don't use two special characters, you are indicating that the string you want to find is any part of the searched string - you are not
positioning it at the top of a certain .
Other symbols include '*', '+' and '?', which represent the number of times a character or a sequence of characters appears repeatedly. They mean "none or
more", "once or more" and "none or once" respectively. Here are a few examples:
"ab*": Indicates that a string has an a followed by zero or several b. ("a", "ab", "abbb",...);
"ab+": Indicates that a string has an a followed by at least one b or more;
"ab?": Indicates a The string has an a followed by zero or one b;
"a?b+$": means that there is zero or one a followed by one or several b at the end of the string.
You can also use a range, enclosed in curly brackets, to indicate the range of repetitions.
"ab{2}": Indicates that a string has an a followed by 2 b ("abb");
"ab{2,}": Indicates that a string has an a followed by at least 2 b;
"ab{3,5}": Indicates that a string has an a followed by 3 to 5 b.
Please note that you must specify the lower limit of the range (eg: "{0,2}" instead of "{,2}"). Also, you may have noticed that '*', '+' and
'?' are equivalent to "{0,}", "{1,}" and "{0,1}".
There is also a '¦', which means "or" operation:
"hi¦hello": indicates that there is "hi" or "hello" in a string;
"(b¦cd )ef": represents "bef" or "cdef";
"(a¦b)*c": represents a string of "a" and "b" mixed strings followed by a "c";
'.' can replace any character:
"a.[0-9]": Indicates that a string has an "a" followed by an arbitrary character and a number;
"^. {3}$": Indicates a string of any three characters (length is 3 characters);
Square brackets indicate that certain characters are allowed to appear at a specific position in a string:
1 |
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You can also use '^' in square brackets to indicate unwanted characters. '^' should be the first one in the square brackets. (For example: "%[^a-zA-Z]%" means
means no letters should appear between the two percent signs).
In order to express verbatim, you must add the escape character '\' before the characters "^.$()¦*+?{\".
Please note that within square brackets, no escape characters are required.
2. Regular expression verification control text box input Character type
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3. Regular expression application examples popular description
************************************************ ******************************
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1 2 3 4 |
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****************** *************************************************** ****************
1 2 |
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************************ *************************************************** *****
1 2 3 |
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****************************************** *****************************************
1 2 3 4 5 |
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** *************************************************** ***************************
1 2 3 4 5 |
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****************** *************************************************** *************
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 |
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# I believe you have mastered the methods after reading these cases, please come for more exciting ones Pay attention to other related articles on php Chinese website!
Related reading:
Implementation steps of using JS to operate HTTP Cookies
About local Web-storage storage Detailed introduction to
#How to set the text font color of CSS
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