I assume it isn’t really variable but a predefined set of possible characters, if so
you can build an alternation class like this
[\.\*-:]
This class would look for either a period, a asteriks, a dash or a colon.
If you ask yourself why this backslash appears then it is because regular expressions uses
special chars for doing something special :-)
Like the period is used as a placeholder for ONE char and the asteriks is used as a multiplier.
And if you want to search for those chars literally you need to escape them by putting a backslash
in front. Now you see, that backslash itself is a special char too and in case you want to look for
a backslash you need to put another one in front.
If you want to understand more about regular expression I would recommend reading
this.
Cheers
Claudia