How do I test for the presents of a character in a string?

I am trying to complete a script that reads a text file and only includes lines that do not start with a "#" symbol. How would you go about it?

Thanks in advance

use grep with the -v option and escape the #. For example, if you are catting "test.txt"

Code:

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cat test.txt | grep -v \#

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this will display all lines within test.txt excluding any that contain a "#".