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I have a plugin activated and working, and I installed and activated another plugin I wrote to communicate with it. However when I run is_plugin_active() I get false returned - does anyone have any idea why and how to rectify it?

EDIT: some basic code. I am in the admin area, and I'm trying to use the functions of the other plugin ultimately. But the initial check is quite basic:

if (is_plugin_active('Plugin2')) {
    echo 'Thanks for installing Plugin2';
} else {
    echo 'Please install Plugin2';

EDIT2: Per the codex, you do NOT need the filepath if you're using in the admin side. But I tried with the full path, as modified here, which also did not work.

if (is_plugin_active('Plugin2/Plugin2.php')) {
    echo 'Thanks for installing Plugin2';
} else {
    echo 'Please install Plugin2';
share|improve this question
Can you post some code or give some context as to how/where you are using it? – Stephen Harris Mar 6 '12 at 18:59
Is this example code the actual code you're using? Because if it is, then your code won't work ... as cale_b answered below, you need the plugin directory and file name (with .php extension) for this to work correctly. – EAMann Mar 6 '12 at 19:15
Is Plugin2 the actual slug of the Plugin, or is it an "example" Plugin slug? Also: in what directory is Plugin2 installed? – Chip Bennett Mar 6 '12 at 19:29
Did you ever figure this out? – codewizard Apr 23 '15 at 15:40
I just checked for a class I knew the plugin to have, using class_exists.. – dama_do_bling Apr 23 '15 at 16:32

Per the WP Codex, you need to be sure you are passing the directory and file:

   If (is_plugin_active('plugin-directory/plugin-file.php')) {
     //plugin is activated
share|improve this answer
Not working, and I'm the admin area anyway so it shouldn't matter. – dama_do_bling Mar 6 '12 at 19:08
Per your question above, it doesn't appear you are passing the file name.... – cale_b Mar 6 '12 at 19:15

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