PHP matches consecutive numbers or letters of regular expressions _ajax related

Regular expression rules:"/ rules need to be written in the middle of 2 slashes /".

• ( . : decimal point) is used to match all characters except line breaks.
• ( \s: Backslash lowercase s) is used to match a single spaces, including tab keys and line breaks;
• ( \s: Backslash capital S) is used to match all characters except a single spaces;
• ( \d: backslash D) is used to match numbers from 0 to 9; You can also write: [0-9]
• ( \w: Backslash lowercase w) used to match letters, numbers, or underscore characters;
• ( \w: the backslash capital W) is used to match all characters that do not match the \w;

meta characters include: + , * , ?

Meta characters are easily confusing to understand, so I did a screenshot of the code results behind

Copy Code code as follows:

The "+" metacharacters specify that their leading characters must occur continuously one or more times

= such as/es+/
Match the "Tesseessssseast12354haeasashaha" string, first with the first letter E, and then the matching s,s must appear one or more times, take a look at the instance screenshot.

The "*" Meta character stipulates that its leading character must appear 0 or more consecutive times

= such as/es*/
Matches the "Tesseessssseast12354haeasashaha" string, first with the first letter E, followed by 0 or successive occurrences, looking at the example.

“?” Metacharacters require that the leading object must appear 0 consecutive times or once

= such as/es?/
Matches the "Tesseessssseast12354haeasashaha" string, first with the first letter e, followed by a 0 or more occurrences (the last letter S does not recur).

Sample code:

Copy Code code as follows:

$str = "Tesseessssseast12354haeasashaha";
echo "=====". $str. "
";
echo "/es+/:". Preg_replace ("/es+/", "-\\0-", $str). "
";
echo "/es*/:". Preg_replace ("/es*/", "-\\0-", $str). "
";
echo "/es?/:". Preg_replace ("/es?/", "-\\0-", $str). "
";
?>

Screenshot of execution results:

In addition, if you feel the meta character "+*"? "It's hard to understand that you can use this {} method instead:"

For example es* we can write es{0,}, and es+ we can write es{1,},es? can be written as es{0,1}, note: When the number of uncertainty is not written (and no space).

Of course we have to specify how many times it can be written like this:es{3} indicates that s appears 3 times

Extrapolate

For example, to replace a contiguous number of spaces for a space , I can write this:preg_replace ("/\s+/", "", $str);
For example, to find the number (integer) in the string:preg_replace ("/\d+/", "(\\0)", $str   ); \\0 is a string value that represents a conforming rule

For example, to find the number with a decimal point in the string :preg_replace ("/\d+\.\d+/", " \\0) ", $str); Here's "\." Indicates the output decimal point

Find a string composed of letters:preg_replace ("/[a-za-z]+/", "(\\0)", $str)

Find a string composed of (alphanumeric):preg_replace ("/[a-za-z]| \d)+/"," (\\0), $str)

The "or" operation in a regular expression, using the " | "

For example, the above example: Find a string consisting of (a letter or a number) ([a-za-z]| \d ) can also be written like this ([a-za-z]| [0-9] )

"^" is treated as a negation operator when it appears inside [],and[^0-9] represents any character other than a number.

When "^" is outside "[]" or "[]", it should be treated as a locator.

locator meaning is like: " ^the ": The beginning must have "the" string; similar: " en$ ": $ sign representation must be en end."

In fact, a careful look at it will find that the regular expression is quite simple, unless the tutorial I wrote is really problematic.