Issues while using Quotes in PHP - php

Question

I have Learnt that Quotes doesn't matter in PHP.
But in the following code, if I try to use single quotes in eval(); I get error, on the other hand code works fine with Double Quotes.
$a = '2';
$b = '3';
$c = '$a+$b';
echo $c.'<br/>';
eval("\$c = \"$c\";");
//eval('\$c = \'$c\';'); //Parse error: syntax error, unexpected T_VARIABLE, expecting T_STRING
echo $c;

Answer 1

PHP.net says that escape sequences are not expanded when using single quotes.

Answer 2

Quotes do matter ;-)
<?php
$color = "red";
echo "My car is $color"; // Outputs "My car is red"
echo 'My car is $color'; // Outputs "My car is $color"
?>

Answer 3

Unlike double quotes, PHP does not parse variables in single quotes.
Example:
$name = 'John';
echo 'hello $name'; // hello $name
echo "hello $name"; // hello John
More Information
FYI, it isn't good idea to use eval in production environment for security reasons.

Answer 4

Using eval is a bad idea but if you are doing this for learning purpose then the correct way is
eval("\$c = \$c;");
.

Answer 5

don't use eval and update your string-quoting skills here:

Answer 6

The following example was lifted from: The PHP Manual
<?php
echo 'this is a simple string';
echo 'You can also have embedded newlines in
strings this way as it is
okay to do';
// Outputs: Arnold once said: "I'll be back"
echo 'Arnold once said: "I\'ll be back"';
// Outputs: You deleted C:\*.*?
echo 'You deleted C:\\*.*?';
// Outputs: You deleted C:\*.*?
echo 'You deleted C:\*.*?';
// Outputs: This will not expand: \n a newline
echo 'This will not expand: \n a newline';
// Outputs: Variables do not $expand $either
echo 'Variables do not $expand $either';
?>