php eval function and performance

Question

Im creating a web app where I want all of the responses to the user stored in a language file for easy editing. So Im using eval() to manage dynamic messages lik so:

$msg = 'Hello $user, your favorite color is $color';

$colors =  array("red","green","blue","yellow");
$users =  array("bob","craig","ted","dirty sanchez");

foreach($users as $key => $user){

 $color = $colors[$key];
 eval("\$newmsg = \"$msg\";");
 echo $newmsg;


}

Im wondering if this is the best approach or if there is a better way?

Lekensteyn · Accepted Answer · 2010-08-28 19:52:37Z

10

Never use that damn eval if not necessary! Your code won't work, you should use sprintf for your purpose.

$messageFormat = 'Hello %s, your favorite color is %s';

$colors =  array("red","green","blue","yellow");
$users =  array("bob","craig","ted","dirty sanchez");
foreach($users as $key => $user){
   $color = $colors[$key];
   $actualMessage = sprintf($messageFormat, $user, $color);
   echo htmlentities($actualMessage);
}

Assuming you're using this for comments or other user-supplied text, I've added htmlentities() to prevent XSS.

edited Aug 28, 2010 at 19:52

answered Aug 28, 2010 at 19:44

Lekensteyn

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1 Comment

NikiC Over a year ago

@websiteguru: There are two reasons why you ought not use eval if you can avoid (and you can avoid nearly always): a) it is a security risk. eval allows executing PHP. If a user could smuggle malicious input into eval, he could execute PHP (and thus, he would have nearly full control over your server.) b) eval is slow, really slow. And eval code is hard to understand. Even though I would call myself an experiences PHP developer it still took some time, till I got what your code does, whereas Lekensteyn's code is perfectly clear.

The Surrican · Accepted Answer · 2010-08-28 19:55:54Z

2

what you need is the printf function. you can define a string and have %s as place holder for a string.

then call

printf($variable, $string1, $string2, $string);

the first %s gets replaced by $string1 and so on.

in your very example i would use vsprintf which returns the string and you can give an array so you can feed it what every array of params and input string you like

heres your example:

   <?
$msg = 'Hello %s, your favorite color is %s';
$colors =  array("red","green","blue","yellow");
$users =  array("bob","craig","ted","dirty sanchez");
foreach($users as $key => $user){
 $color = $colors[$key];
 $newmsg = vsprintf($msg,array($user,$color));
 echo $newmsg."\n";
}

?>

answered Aug 28, 2010 at 19:55

The Surrican

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Comments

shamittomar · Accepted Answer · 2010-08-28 19:49:09Z

0

I prefer this way:

<?php

$msg = 'Hello [USER], your favorite color is [COLOR]';

$colors =  array("red","green","blue","yellow");
$users =  array("bob","craig","ted","dirty sanchez");

foreach($users as $key => $user)
{
    $color = $colors[$key];

    $newmsg = str_replace(array('[USER]', '[COLOR]'), array($user, $color), $msg);
    echo $newmsg;
}
?>

answered Aug 28, 2010 at 19:49

shamittomar

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1 Comment

websiteguru Over a year ago

While not what I was looking for, this is interesting. How would this compare in performance to the sprintf solution? Specifically if there were a large amount of variables used.

Gazler · Accepted Answer · 2010-08-28 20:04:34Z

0

$colors =  array("red","green","blue","yellow");
$users =  array("bob","craig","ted","dirty sanchez");
$messages = array_combine($colors, $users);

foreach ($messages as $color => $user)
{
     echo "Hello $user, your favourite color is $color";
}

Using array_combine which creates arrays in the format $keys => $values making the following array:

"red" => "bob",
"green" => "craig",
"blue" => "ted",
"yellow" => "dirty sanches"

edited Aug 28, 2010 at 20:04

answered Aug 28, 2010 at 19:56

Gazler

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Comments

Mai Siêu Bông · Accepted Answer · 2020-10-15 11:40:37Z

0

You can use the strtr function

$msg = 'Hello @user, your favorite color is @color';
echo strtr($msg, array('@user'=>'bob', '@color'=>'red'));

Output:

Hello bob, your favorite color is red

answered Oct 15, 2020 at 11:40

Mai Siêu Bông

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