Find position of a character in a string - forum topic by jacky464

Hi Everyone,
Anyone could help with this question? I want to select part of a string. The string is like abc_def_dfsfs_dfdfasdfs_fsdfs_fbc_fsd_sfs_sdfsd.
I want to select fbc and fsd, but the issue is the number of characters before is not costant. For example, before fbc, there could be a 7 character string as well. I think the thing I should use to position is '_', but there are like 7 underscores in the whole string. How can I do it?
Thanks for any advice!