what is that mean in perl language ? $testModule =~ s@/@::@ig;

I am a newbie of perl and I‘m reading some perl codes, I find one line below I could't understand, can anyone tell what is that mean " s@/@::@ig". I know '=~' is try to match some regular expression. usually I would see code like 's///gi', so I was a little confused of the following code. can anyone help to elaborate? thanks.

$testModule =~ s@/@::@ig;