How to delete text from file using preg_replace() function in PHP ?

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Given a file containing some elements and the task is to delete the content of the file using preg_replace() function. The preg_replace() function is searches the string pattern in the file and if string pattern found then it replace with the required string. In simple words it can modify the contents of a file.

Syntax:

preg_replace( $pattern,  $replacement, $subject);

Parameters:

$pattern: It contains the string we have to replace.
$replacement: It contains the string that will replace the existing string.
$subject: It contains the main string file where need to remove the string.

We have created a text file named as fruits.txt
fruits.txt

mango
apple
papaya
guava
apple
grapes
mango
apple

Program 1: This program removes all the strings from the given file.

<?php 
  
$a = 'fruits.txt'; 
$b = file_get_contents('fruits.txt'); 
echo "File contents before using "
        . "preg_replace() function<br>"; 
echo $b; 
echo "<br><br>File contents after using "
        . "preg_replace() function<br> "; 
$c = preg_replace('/[a-z]/', '', $b); 
echo $c; 
file_put_contents($a, $c); 
?> 

Output:

File contents before using preg_replace() function
mango apple papaya guava apple grapes mango apple

File contents after using preg_replace() function

Program 2: This program deletes a specific content from the file using preg_replace() function.

<?php 
  
$a = 'fruits.txt'; 
   
$b = file_get_contents('fruits.txt'); 
  
echo "File contents before using "
        + "preg_replace() function<br>"; 
echo $b; 
  
echo "<br><br>File contents after using "
        + "preg_replace() function<br>"; 
  
$c = preg_replace('/[a]/', '', $b); 
echo $c; 
  
file_put_contents($a, $c);  
?> 

Output:

File contents before using preg_replace() function
mango apple papaya guava apple grapes mango apple

File contents after using preg_replace() function
mngo pple ppy guv pple grpes mngo pple

Program 3: This program deletes the entire word from the file.

<?php 
  
$a = 'fruits.txt'; 
   
$b = file_get_contents('fruits.txt'); 
  
echo "File contents before using "
        . "preg_replace() function<br>"; 
echo $b; 
  
echo "<br><br>File contents after using "
        . "preg_replace() function<br>"; 
  
$c = preg_replace('/apple/', '', $b); 
echo $c; 
  
file_put_contents($a, $c);  
?> 

Output:

File contents before using preg_replace() function
mango apple papaya guava apple grapes mango apple

File contents after using preg_replace() function
mango papaya guava grapes mango