PHP writing vars to txt file, results in duplicate commas/punctuation - php

Question

I've got some data posted to a php file, and I need to save/append that data separated by commas to a text file. That's all fine and dandy and should be straightforwards, except for when I check the file I see that every comma has been written twice: once where it needs to be, and then again after the appended data but as a group of commas.
Here's what I've got:
<form action="signup-submit.php" method="post">
<fieldset>
<legend>New User Signup:</legend>
<label>Name:</label>
<input type="text" name="name" size="16" autofocus required/> <br/>
<label>Gender:</label>
<label><input type="radio" name="gender" value="m" /> Male</label>
<label><input type="radio" name="gender" value="f" checked /> Female</label> <br />
<label>Age: <input type="text" name="age" size="6" maxlength="2" required></label><br/>
<label>Personality Type: <input type="text" name="pType" maxlength="4" size="6" required/></label><br/>
<label>
Favorite OS:
<select name="os">
<option value="windows">Windows</option>
<option value="mac">Mac OS X</option>
<option value="linux">Linux</option>
</select>
</label><br/>
<label>
Seeking age:
<input name="min" type="text" size="6" maxlength="2" placeholder="min" required/>
to
<input name="max" type="text" size="6" maxlength="2" placeholder="max" required/>
</label><br/>
<input type="submit" value="Sign up"/>
</fieldset>
</form>
^that code posts the "user data" to signup-submit.php where it is stored into variables by the same var names.
$name = $_POST["name"];
$age = $_POST["age"];
$gender = $_POST["gender"];
$pType = $_POST["pType"];
$os = $_POST["os"];
$min = $_POST["min"];
$max = $_POST["max"];
$c = chr(44);
$s = "$name$c$age$c$gender$c$pType$c$os$c$min$c$max";
file_put_contents("single.txt", $s, FILE_APPEND);
?>
and the text file will unfailingly duplicate the commas as such:
Byron,21,m,INTP,windows,18,23,,,,,,
the variables are simply data posted to this file from a previous page. I've also tried every which way under the sun to save the data. In fact, if I write only text directly, I get no problems. When I used the csv function I got just commas and no data despite or so I believed formatting it correctly.

Answer 1

That's probably because sometime all your variables are empty, and you FILE_APPEND just commas.
To solve this do:
if (!empty($name) && !empty($age) && ...) {
$s = "$name,$age,$gender,$pType,$os,$min,$max";
file_put_contents("single.txt", $s, FILE_APPEND);
}
If these values are user input always double check them. PHP offers standard functions to sanitize: Sanitize Filters, also you will need input validation with custom rules (for example to check if a variable is within a certain range, but this is a different question).