How Does PHP Handle Periods in Variable Names from GET, POST, and Cookies?

PHP Variable Names and Character Replacement

In PHP, it is common practice to pass request fields or cookies with a period/dot (.) in their names. However, PHP automatically replaces these dots with underscores (_). This behavior arises from PHP's use of dots for variable name concatenation.

Explanation

According to PHP documentation, the dot character (.) is not permitted in variable names. This can lead to unexpected behavior when concatenating variables, as shown in the example PHP code below:

$varname.ext;  /* invalid variable name */

In the above example, PHP will interpret the right-hand side (ext) as a string. To prevent this, PHP replaces dots in incoming variable names with underscores.

Consequences

This replacement behavior affects not only GET and POST parameters but also cookies. For example, if a cookie with the name "x.y" is set, PHP will automatically change it to "x_y" in its internal representation.

Solutions

While it is not possible to prevent PHP's dot-to-underscore replacement, there are workarounds to retrieve the original variable name with dots. One solution is to use the str_replace() function to replace the underscores back to dots after reading the variables, as suggested in dawnerd's comment.

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