Conditional execution of steps

[bistace]

Hello and thank you for developping Bpipe, it is very useful to me.

Would Bpipe be able to execute some steps only if some conditions are met?

As an example, let's imagine that user specifies an optional file on the command line, is there any way to tell Bpipe to execute a specific step if this file exists on the filesystem?

Another usecase would be, again as an example, to test if fasta headers contain non-alphanumeric characters and format them in a specific step if some are found but otherwise go to the next step?