cmd=testIncIntString
str=foo23       amt=1  keep=true  # new_str=foo24
str=foo23bar    amt=3  keep=true  # new_str=foo26
str=foo23bar34  amt=1  keep=true  # new_str=foo2335


str=foo23bar34  amt=1  keep=false  # new_str=2335
str=alpha88     amt=11 keep=false  # new_str=99