Combine multiple click function into one function

JavaScript
6 
<!DOCTYPE html>
    <html lang="en">
    <head>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <meta http-equiv="X-UA-Compatible" content="ie=edge">
        <title>Learn Javascript</title>
        <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.1/jquery.min.js">
    </script>
 
</head>

<select name=master[] id=master class="master" multiple="multiple" size='23'>
<?php   
    $file = fopen("temp.csv", "r");
    while (($row = fgetcsv($file, 0, ",")) !== FALSE) {
        $master = $row[0];
?>
    <option><?php echo $master; ?></option>
<?php
    }
?>
</select> 
<form action="update.php" method="post">
    <input type=button class="master" name=b1 id=b1 value='Move >'>
    <input type=button class="master" name=b1 id=b1 value='< Remove'>&nbsp;&nbsp;&nbsp;&nbsp;
<select name=purchases[] id=purchases multiple="multiple" class=master>
<?php   
    $file = fopen("purchases.csv", "r");
    while (($row = fgetcsv($file, 0, ",")) !== FALSE) {
        $purchases = $row[0];
?>
    <option value="<?php echo $purchases;?>"><?php echo $purchases;?></option>
<?php
    }

<form action="update.php" method="post">
    <input type=button class="master" name=b3 id=b3 value='Move >'>
    <input type=button class="master" name=b4 id=b4 value='< Remove'>&nbsp;&nbsp;&nbsp;&nbsp;
<select name=salaries[] id=salaries multiple="multiple" class=master>
<?php   
    $file = fopen("salaries.csv", "r");
    while (($row = fgetcsv($file, 0, ",")) !== FALSE) {
        $salaries = $row[0];
?>
    <option value="<?php echo $salaries;?>"><?php echo $salaries;?></option>
<?php
    }
?>
</select>
&nbsp;&nbsp;&nbsp;&nbsp;<input type="submit" value="Save File" name="submit">
</form>

The csv files you can populate with any data the upload.php file to save data you can help me here as well to get it into a simplify (there is more than 24 but here I just used 2 as an example) and thank you for still trying

<?php
header("Location:".$URL.'index.php');

if ($_POST['purchases']) {
$purchases = $_POST['purchases'];
$purchasesunique = array_unique($purchases);
sort($purchasesunique);
foreach ($purchasesunique as $key => $value) {
    $result.=$value."\n";
}
file_put_contents('purchases.csv',$result);
}

if ($_POST['salaries']) {
$salaries = $_POST['salaries'];
$salariesunique = array_unique($salaries);
sort($salariesunique);
foreach ($salariesunique as $key => $value) {
    $result.=$value."\n";
}
file_put_contents('salaries.csv',$result);
}


?>