PHP Strings

<?php

//1. how to use mail function

            //create short variable names

            $name=$_POST['name'];

            $email=$_POST['email'];

            $feedback=$_POST['feedback'];

            //set up some static information

            //$toaddress = "feedback@example.com";

            $toaddress = "luoxu@qq.com";

            $subject = "Feedback from web site";

            $mailcontent = "Customer name: ".filter_var($name)."\n".

            "Customer email: ".$email."\n".

            "Customer comments:\n".$feedback."\n";

            $fromaddress = "From: webserver@example.com";

            //invoke mail() function to send mail

            mail($toaddress, $subject, $mailcontent, $fromaddress);

//2.Trimming Strings chop(), ltrim(), trim()

            $str= "inert               air   ";

            echo $str;

            $str = trim($str);

            chop($str);

            echo "<br>";

//3.  htmlspecialchars()  conflict with html tags

             $new = htmlspecialchars("<a href='test'>Test</a>");

             echo $new; // &lt;a href='test'&gt;Test&lt;/a&gt;

             $new = htmlspecialchars("<a href='test'>Test</a>", ENT_QUOTES);

             echo $new; // &lt;a href='test'&gt;Test&lt;/a&gt;

            echo nl2br("foo isn't\n bar");  //foo isn't<br />bar  translate \r\n to <br>

            echo nl2br(htmlspecialchars($feedback));  // it will display as newline（line feed）we should use them in this order

            echo htmlspecialchars(nl2br($feedback));  //it will display <br> literally

             echo '<hr>';

//4.output string

            $total =12.345565;

             echo "The total amount of order is $total";

             printf("The total amount of order is %s ",$total );  //output a formatted string

             printf("The total amount of order is %.2f ",$total );  //output a formatted string  12.35

             $s =sprintf("The total amount of order is %+s",$total ); // return a formatted string

            echo $s;

            echo '<hr>';

//5.String case function

            $str = "feedback from Website luoxu" ;

            echo  strtoupper($str);

            echo  strtolower($str);

            echo  ucfirst($str); //Feedback from Website luoxu

            echo  ucwords($str); //Feedback From Website Luoxu

            echo "<hr>";

//6.Joining and Spliting Strings with string function

            $email = "luoXU@qQ.coM";

            $emailArr= explode('@',$email);

            print_r($emailArr); //Array ( [0] => luoXU [1] => qQ.coM )

            if(strtolower($emailArr[1]) == 'qq.com'){

                $toaddress = 'bob@example.com';

            }

            array_walk($emailArr,"toLowerCase");

            function toLowerCase(&$value ){  // needs to add & in front of $value which will affect the $emailArr

                $value = strtolower($value);

            }

            print_r($emailArr); //Array ( [0] => luoxu [1] => qq.com )

            $newEmail = implode('@',$emailArr);

            echo $newEmail;  //luoxu@qq.com

//7.strtok()

            $str = 'Hello to all of Ukraine'; //split the string with ' ' delimiter as the first substring(token),

            // for the second token, you only need to pass the delimiter,

            //because strtok() keeps its own internal pointer to its place in the string

            echo strtok($str, ' ').' '.strtok(' ').' '.strtok(' '); //Hello to all

            $string = "This  is\tan example\nstring";

            /* Use ' ' as tokenizing characters as well  */

            $tok = strtok($string, " ");

            while ($tok !== false) {

                echo "Word=$tok<br />";

                $tok = strtok(" ");

            }

            //Word=This

            //Word=is an

            //Word=example string

            /* Use tab and newline as tokenizing characters as well  */

            $tok = strtok($string, " \n\t");

            while ($tok !== false) {

                echo "Word=$tok<br />";

                $tok = strtok(" \n\t");

            }

            //Word=This

            //Word=is

            //Word=an

            //Word=example

            //Word=string

            echo "<hr>";

//8.substr()

            $test = 'Your customer service is excellent';  //string position starts from 0

            echo substr($test,1); //our customer service is excellent

            echo substr($test,-9); // excellent

            echo substr($test,5,4);  //cust

            echo substr($test,5,-13); //customer service

            echo $test[1]; //o, we can take a string as a  array

            echo "<hr>";

//9.Comparing Strings

            $str1 = "hello";

            $str2 = "hello";

            $str3 = "aello";

            $str4 = "Hello";

            echo strcmp($str1,$str2);  //0

            echo strcmp($str1,$str3).'<br>';  //return a number that is greater than 0 if str1 > str2 alphabetically

            echo strcmp($str1,$str4);  // H < h in ASCII a number that is greater than 0

            echo strcasecmp($str1,$str4).'<br>'; //0

            $str5 ='6';

            $str6 = '12';

            echo strcasecmp($str5,$str6); // result = str6 - str5 ASCII value    return 5

            echo strnatcmp($str5,$str6); // result = str6 - str5  integer value  return -1

            echo strlen($str1);  //5

            echo "<hr>";

//10. Matching and Replacing substring with string function

            $email  = 'name@example.com';

            $domain = strstr($email, '@');

            echo $domain; // prints @example.com

            $user = strstr($email, '@', true); // As of PHP 5.3.0

            echo $user; // prints name

            echo stristr($email,M); //me@example.com

            echo stristr($email,M,true); //na

            echo strchr($email,'e'); //e@example.com

            echo strpos($email,'m'); //2 starts from 0, the position first occurrence of the needle

            echo strrpos($email,'m'); //15  starts from the end , the position first occurrence of the needle reverse

            $result = strpos($email,'A');  //not found return false

            if($result === false){  //($result == false)is wrong,

                // because if we find 'n' in the string , it returns 0, however (0 == false) is true

                echo 'not found';

            }else{

                echo "Found at position:".$result;

            }

            echo "<hr>";

//11.str_replace();

            $bodytag = str_replace("%body%", "black", "|body text='%body%'|");

            echo $bodytag; //|body text='black'|

            $vowels = array("a", "e", "i", "o", "u", "A", "E", "I", "O", "U");

            $onlyconsonants = str_replace($vowels, "", "Hello World of PHP");

            echo $onlyconsonants;//Hll Wrld f PHP

            //If search and replace are arrays, then str_replace() takes a value from each array and uses them to search and replace on subject.

            $phrase  = "You should eat fruits, vegetables, and fiber every day.";

            $healthy = array("fruits", "vegetables", "fiber");

            $yummy   = array("pizza", "beer", "ice cream");

            $newphrase = str_replace($healthy, $yummy, $phrase);

            echo $newphrase;  //You should eat pizza, beer, and ice cream every day

            $str = str_replace("ll", "", "good golly miss molly!", $count);

            echo $str; //good goy miss moy!

            echo $count; //2   2 of 'll' was matched

            echo "<hr>";

            //replace the substr of string with replacement.take substr_replace('bananas','xyzZ',1,2) as an example

            //1. get the substr of the string removing the parts from start to end(length=end-start)  substr = b(an)anas, an is removed

            //2. insert replacement into substr from start position 1.

            echo substr_replace('bananas','xyz',1); //bxyz replace the substr of bananas starting from 1 with xyz

            echo substr_replace('bananas','xyzZ',1,2); //bxyzZanas replace the substr of bananas starting from 1 to 3(length is 2) with xyz

            echo substr_replace('bananas','xyz',-1); //bananaxyz replace the substr of bananas starting from 1 to 3(length is 2) with xyz

            echo substr_replace('bananas','xyz',-1,-2); //bananaxyzs

            echo substr_replace('bananas','xyz',4,1); //bbanaxyzas

//12.Regular Expression (better to use double quotation mark for strings) less sufficient than string function with similar functionality

       //https://regex101.com/ for testing regex

      //delimiter:  /pattern/    or #pattern#

         // using backslash \ to escape / eg: /http:\/\//

        //Character Class and Type

            //1.    /.at/ . means matching a single character, eg:cat,mat,#at,

                    //  /.[a-z]/ when a dot is used at the beginning or end of a Character class, it loses its special wildcardmeaning and becomes just a literal dot

            //2.    /[a-z]at/ [] means matching a a single  character in the square bracket that belongs to a-z ,eg: apple

            //3.    /[^a-z]at/ ^ (caret) in the square bracket means not to matching any of a single  character that belongs to a-z

            //4. [[:alnum:]] means alphanumeric character

            //4. [[:lower:]] means lower case letters

            //5. [[:alpha]1-5] means a class that may contain an alphabetically character or any of the digits from 1-5

     //Repetition  the three symbols should appear directly after the part of the expression that it applies to

            //1. *  means 0 or more times

            //2. +  means 1 or more times

            //3. ? means 0 or 1 times

            //eg: /[[:alnum:]+]/  means at least one alphanumeric character

      //Subexpression   using the parenthesis to group certain words (substring) is called inside ()

            //eg: /(very )*large/  means 'large', 'very large', 'very very large'

            //counted subExpression  using curly braces to show repeated times

            //eg: /(very){3}/  3 times exactly

            //eg: /(very){1,3}/ very can be repeated 1-3 times, it is 'very' , 'veryvery', 'veryveryvery'

            //eg: /(very){2,}/ very can be repeated at least 2 times, it is 'veryvery', 'veryveryvery', and so on

      //Anchoring to the beginning or end of a string

            //1. ^ caret outside of [] is used at the start of a regular expression to show that it must appear at the beginning of a searched string

            //2. $  at the end

            //eg: /^bob/ a string starts with bob

            //eg: /com$/ a string ends with com

            //eg: /^[a-z]$]/ a string contains a single character between a and z

     //Branching

            // /com|edu|net/ matched one of those three is ok

     //Matching literal special character

            //1. using backslash \ to escape special character

            // "\\\\" => '\\' => '\' Matching one '\' needs three \\\ to escape

            // "\\\$" => '\$' => '$' Matching one '\' needs three \\\ to escape

     //A Summary of Meta Characters used in PCRE regular expression

            //1. outside of square bracket : \ ^ $ . | ( )  * + { } ?

            //2. inside of square bracket : \ ^ -

     //Back Reference

           //1. /^([a-z]+) \1 black sheep /  "blarge blarge black sheep" matched

      // functions in PHP for PCRE regular expression

            //find substring

            preg_match('/(foo)(bar)(baz)/', 'foobarbaz', $matches, PREG_OFFSET_CAPTURE);

            print_r($matches);

            //Array ( [0] => Array ( [0] => foobarbaz [1] => 0 )

                //   [1] => Array ( [0] => foo [1] => 0 )

                // [2] => Array ( [0] => bar [1] => 3 )

                // [3] => Array ( [0] => baz [1] => 6 ) )

            preg_match('/(a)(b)*(c)/', 'ac', $matches);

            var_dump($matches);

            preg_match('/(a)(b)*(c)/', 'ac', $matches, PREG_UNMATCHED_AS_NULL);

            var_dump($matches);

            //replace substring

            $string = 'April 15, 2003';

            $pattern = '/(\w+) (\d+), (\d+)/i';

            $replacement = '${1}1,$3';  //leave the first group(April),plus a literal 1 and ',' and the third group(2003)

            echo preg_replace($pattern, $replacement, $string); //April1,2003

            $string = 'The quick brown fox jumps over the lazy dog.';

            $patterns = array();

            $patterns[0] = '/quick/';

            $patterns[1] = '/brown/';

            $patterns[2] = '/fox/';

            $replacements = array();

            $replacements[2] = 'bear';

            $replacements[1] = 'black';

            $replacements[0] = 'slow';

            echo preg_replace($patterns, $replacements, $string); //The bear black slow jumps over the lazy dog.

            //splitting strings

            $address = 'username@example.com';

            $arr = preg_split('/\.|@/', $address);

            print_r($arr);  //Array ( [0] => username [1] => example [2] => com )
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PHP Strings

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