Learn and practice PHP (16)

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Perl compatible regular expressions

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1. Function:

preg_match(): Indicates whether the pattern matches the string. Once a match is found, it returns 1, otherwise it returns 0

preg_match_all(): Find all Match

preg_replace(): implement search and replacement

2. Simple mode:
1. Literal: is a value that is written exactly as it is interpreted. For example, the pattern a will match the letter a, ab will match ab, etc.

1. Delimiter: Can be any character except alphanumeric or backslash, the same character must be used to mark the beginning and end of the pattern. Usually forward slash (/)

2. Metacharacter:
   

3. Quantifier:
   

4. Common character categories:
   

   
   3. Practice:

   1. Single match - pcre.php

<code><span><span>html</span><span>lang</span>=<span>"en"</span>></span><span>head</span>><span>meta</span><span>charset</span>=<span>"UTF-8"</span>><span>title</span>>Testing PCRE<span><span>title</span>></span><span><span>head</span>></span><span>body</span>><span><span><?php </span><span># Script 14.1- pcre.php</span><span>if</span>(<span>$_SERVER</span>[<span>'REQUEST_METHOD'</span>] == <span>'POST'</span>)
        {
            <span>$pattern</span> = trim(<span>$_POST</span>[<span>'pattern'</span>]);
            <span>$subject</span> = trim(<span>$_POST</span>[<span>'subject'</span>]);

            <span>echo</span><span>"<p>The result of checking<br><b>$pattern</b><br>aganist<br>$subject<br>is</p>"</span>;

            <span>if</span>(preg_match(<span>$pattern</span>, <span>$subject</span>))
            {
                <span>echo</span><span>'TRUE!'</span>;
            }<span>else</span>{
                <span>echo</span><span>'FALSE!'</span>;
            }
        }
    <span>?></span></span><span>form</span><span>action</span>=<span>"pcre.php"</span><span>method</span>=<span>"post"</span>></span><span>p</span>>Regular Expression Pattern: <span>input</span><span>type</span>=<span>"text"</span><span>name</span>=<span>"pattern"</span><span>value</span>=<span>"<?php if(isset($pattern)) echo htmlentities($pattern); ?>"</span><span>size</span>=<span>"40"</span>>(include the delimiters)<span><span>p</span>></span><span>p</span>>Test Subject: <span>input</span><span>type</span>=<span>"text"</span><span>name</span>=<span>"subject"</span><span>value</span>=<span>"<?php if(isset($subject)) echo htmlentities($subject); ?>"</span><span>size</span>=<span>"40"</span> /><span><span>p</span>></span><span>input</span><span>type</span>=<span>"submit"</span><span>name</span>=<span>"submit"</span><span>value</span>=<span>"Test!"</span>><span><span>form</span>></span><span><span>body</span>></span><span><span>html</span>></span></code>

- to implement email verification: emails start with letters, numbers or underscores, and periods (.) or dashes.

2. All matches - matches.php

<code><span><span>html</span><span>lang</span>=<span>"en"</span>></span><span>head</span>><span>meta</span><span>charset</span>=<span>"UTF-8"</span>><span>title</span>>Testing PCRE<span><span>title</span>></span><span><span>head</span>></span><span>body</span>><span><span><?php </span><span># Script 14.1- pcre.php</span><span>if</span>(<span>$_SERVER</span>[<span>'REQUEST_METHOD'</span>] == <span>'POST'</span>)
        {
            <span>$pattern</span> = trim(<span>$_POST</span>[<span>'pattern'</span>]);
            <span>$subject</span> = trim(<span>$_POST</span>[<span>'subject'</span>]);

            <span>echo</span><span>"<p>The result of checking<br><b>$pattern</b><br>aganist<br>$subject<br>is</p>"</span>;

            <span>if</span>(preg_match_all(<span>$pattern</span>, <span>$subject</span>, <span>$matches</span>))
            {
                <span>echo</span><span>'TRUE!'</span>;
                <span>echo</span><span>'<pre class="brush:php;toolbar:false">'

.print_r($matches, 1).'

'

; }else{ echo'FALSE!'; } } ?>formaction="matches.php"method="post">p>Regular Expression Pattern: inputtype="text"name="pattern"value=""size="40">(include the delimiters)p>p>Test Subject: textareaname="subject"rows="5"cols="40">if(isset($subject)) echo htmlentities($subject); ?>textarea>p>inputtype="submit"name="submit"value="Test!">form>body>html>

3. Matches and replacements - replace.php

<code><span><span>html</span><span>lang</span>=<span>"en"</span>></span><span>head</span>><span>meta</span><span>charset</span>=<span>"UTF-8"</span>><span>title</span>>Testing PCRE<span><span>title</span>></span><span><span>head</span>></span><span>body</span>><span><span><?php </span><span># Script 14.1- pcre.php</span><span>if</span>(<span>$_SERVER</span>[<span>'REQUEST_METHOD'</span>] == <span>'POST'</span>)
        {
            <span>$pattern</span> = trim(<span>$_POST</span>[<span>'pattern'</span>]);
            <span>$subject</span> = trim(<span>$_POST</span>[<span>'subject'</span>]);
            <span>$replace</span> = trim(<span>$_POST</span>[<span>'replace'</span>]);

            <span>echo</span><span>$subject</span>;

            <span>echo</span><span>"<p>The result of replacing<br><b>$pattern</b><br>with<br>$replace<br>in<br>$subject<br><br>"</p></span>;

            <span>if</span>(preg_match(<span>$pattern</span>, <span>$subject</span>))
            {
                <span>echo</span> preg_replace(<span>$pattern</span>, <span>$replace</span>, <span>$subject</span>).<span>''</span>;
            }<span>else</span>{
                <span>echo</span><span>'The pattern was not found!'</span>;
            }
        }
    <span>?></span></span><span>form</span><span>action</span>=<span>"replace.php"</span><span>method</span>=<span>"post"</span>></span><span>p</span>>Regular Expression Pattern: <span>input</span><span>type</span>=<span>"text"</span><span>name</span>=<span>"pattern"</span><span>value</span>=<span>"<?php if(isset($pattern)) echo htmlentities($pattern); ?>"</span><span>size</span>=<span>"40"</span>>(include the delimiters)<span><span>p</span>></span><span>p</span>>Replacement: <span>input</span><span>type</span>=<span>"text"</span><span>name</span>=<span>"replace"</span><span>value</span>=<span>"<?php if(isset($replace)) echo htmlentities($replace); ?>"</span><span>size</span>=<span>"40"</span>><span><span>p</span>></span><span>p</span>>Test Subject: <span>textarea</span><span>name</span>=<span>"subject"</span><span>rows</span>=<span>"5"</span><span>cols</span>=<span>"40"</span>><span><span><?php </span><span>if</span>(<span>isset</span>(<span>$subject</span>)) <span>echo</span> htmlentities(<span>$subject</span>); <span>?></span></span><span><span>textarea</span>></span><span><span>p</span>></span><span>input</span><span>type</span>=<span>"submit"</span><span>name</span>=<span>"submit"</span><span>value</span>=<span>"Test!"</span>></span><span><span>form</span>></span><span><span>body</span>></span><span><span>html</span>></span></code>

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